Dissertations / Theses on the topic 'Exoplanets'

La detecció de la primera estrella binària més de 200 anys enrere va representar l'inici de tot un nou camp de l'astrofísica dedicat a l'estudi de l'evolució i les interaccions d'aquests sistemes, fent servir com a principal eina l'anàlisi del moviment reflex causat pel company orbitant. Va ser només qüestió de temps que els instruments de mesura assolissin un nivell de precisió prou elevat per a detectar els moviments induïts per planetes sobre les seves estrelles. El descobriment del primer exoplaneta fa quasi tres dècades va suposar la creació d'un reguitzell de projectes dedicats a la cerca de nous mons, els quals estan produint un munt de dades que també estan essent utilitzades amb la finalitat d'estudiar diferents propietats de les estrelles. L'objectiu principal d'aquesta tesi és l'estudi i caracterització d'exoplanetes, estrelles i sistemes estel·lars mitjançant l'anàlisi de dades provinents de projectes dedicats a la cerca d'exoplanetes amb instruments d'alta precisió. Aquest és el cas dels projectes CARMENES i TESS, que tenen l'objectiu de trobar planetes fent servir el mètode de la velocitat radial i la detecció de trànsits planetaris, respectivament, posant un èmfasi especial en estrelles de tipus M. Primerament, hem desenvolupat un nou mètode per a determinar les propietats de les taques estel·lars i dels moviments convectius en estrelles M usant la variabilitat induïda per l'activitat estel·lar. En particular, hem modelat les velocitats radials cromàtiques i la fotometria de l'estrella YZ CMi fent servir el software de modelatge d'activitat estel·lar StarSim. L'anàlisi ha revelat la presència d'una gran taca polar amb una temperatura 200 K inferior a la de l'estrella, trobant també que el moviment convectiu de l'estrella podria tenir un moviment invers a l'esperat. A partir d'un anàlisi combinat de velocitats radials antigues i de CARMENES, en aquesta tesi presentem la detecció d'un mini Neptú i una superterra al voltant de les estrelles M LSPM J2116+0234 i GJ 686, respectivament, just fora del límit intern de les respectives zones habitables. Per tal d'evitar la determinació esbiaixada de les característiques dels planetes, hem modelat els senyals planetaris conjuntament amb els provinents de l'activitat estel·lar, els quals hem modelat amb soroll correlat. Els paràmetres orbitals resultants d'aquesta anàlisi corresponen a períodes orbitals de 14.45 d i 15.53 d, i masses mínimes de 12.8 i 6.6 masses terrestres pels planetes LSPM J2116+0234b i GJ 686b, respectivament. El mètode de velocitats radials emprat per a detectar exoplanetes amb CARMENES també permet la detecció de sistemes múltiples. En aquest treball, anunciem el descobriment de 17 nous sistemes, dels quals determinem les òrbites espectrals. La mostra està formada per 15 sistemes binaris (5 amb companyes no detectades) i 3 sistemes triples. Hem determinat que les companyes no detectades de dues de les binàries tenen masses mínimes compatibles amb una nana marró, i demostrem que un sistema binari està format per una nana blanca i una estrella M. Un anàlisi conjunt de velocitats radials i astrometria ens ha permès determinar les masses d'un sistema binari, el qual esdevé un dels sistemes més joves amb masses mesurades. Per últim, hem usat fotometria de TESS per a derivar el temps d'eclipsi de 16 binàries eclipsants excèntriques. Mitjançant l'anàlisi de l'evolució de les diferències entre el temps d'eclipsi primari i secundari amb el temps, hem determinat el moviment apsidal de 10 sistemes, 5 dels quals són mesurats per primer cop. Hem comparat les nostres mesures amb prediccions teòriques obtenint una concordança excel·lent. Hem sigut capaços de mesurar el terme relativista amb prou precisió per a testejar la relativitat general amb aquest mètode per primer cop.
La detección de la primera estrella binaria hace más de 200 años representó el inicio de un nuevo campo en la astrofísica dedicado al estudio de la evolución y las interacciones de estos sistemas, usando como principal herramienta el análisis del movimiento reflejo causado por el cuerpo orbitante. Solo fue cuestión de tiempo que los instrumentos de medida alcanzaran un nivel de precisión suficientemente elevado como para detectar los movimientos inducidos por planetas sobre sus estrellas. El descubrimiento del primer exoplaneta hace casi tres décadas supuso la creación de un seguido de proyectos dedicados a la búsqueda de nuevos mundos, los cuales están produciendo un montón de datos que se están usando con la finalidad de estudiar diferentes propiedades de las estrellas. El objetivo principal de esta tesis es el estudio y caracterización de exoplanetas, estrellas y sistemas estelares mediante el análisis de datos provenientes de proyectos dedicados a la busca de exoplanetas con instrumentos de alta precisión. Este es el caso de los proyectos CARMENES y TESS, que tienen el objetivo de encontrar planetas usando el método de la velocidad radial y la detección de tráficos planetarios, respectivamente, poniendo un énfasis especial en estrellas tipo M. Primeramente, hemos desarrollado un nuevo método para determinar las propiedades de las manchas estelares y de los movimientos convectivos en estrellas M usando la variabilidad inducida por la actividad estelar. En particular, hemos modelado las velocidades radiales cromáticas y la fotometría de la estrella YZ CMi usando el software de modelado de actividad estelar StarSim. El análisis ha revelado la presencia de una gran mancha polar con una temperatura 200 K inferior a la de la estrella, encontrando también que el movimiento convectivo de la estrella podría tener un movimiento inverso al esperado. A partir de un análisis combinado de velocidades radiales antiguas y de CARMENES, en esta tesis presentamos la detección de un mini Neptuno y una supertierra alrededor de las estrellas M LSPM J2116+0234 y GJ 686, respectivamente, justo fuera del límite interno de las respectivas zonas habitables. Para evitar la determinación sesgada de las características de los planetas, hemos modelado las señales planetarias conjuntamente con las provenientes de la actividad estelar, los cuales hemos modelado con ruido correlacionado. Los parámetros orbitales resultantes de este análisis corresponden a periodos orbitales de 14.45 d y 15.53 d, y masas mínimas de 12.8 y 6.6 masas terrestres para los planetas LSPM J2116+0234b y GJ 686b, respectivamente. El método de velocidades radiales empleado para detectar exoplanetas con CARMENES también permite la detección de sistemas múltiples. En este trabajo, anunciamos el descubrimiento de 17 nuevos sistemas, de los cuales determinamos las órbitas espectrales. La muestra está formada por 15 sistemas binarios (5 con compañeras no detectadas) y 3 sistemas triples. Hemos determinado que las compañeras no detectadas de dos de las binarias tienen masas mínimas compatibles con una enana marrón, y demostramos que un sistema binario está formado por una enana blanca y una estrella M. Un análisis conjunto de velocidades radiales y astrometría nos ha permitido determinar las masas de un sistema binario, el cual es uno de los sistemas más jóvenes con masas medidas. Por último, hemos usado fotometría de TESS para determinar el tiempo de eclipse de 16 binarias eclipsantes excéntricas. Mediante el análisis de la evolución de las diferencias entre el tiempo de eclipse primario y secundario con el tiempo, hemos determinado el movimiento apsidal de 10 sistemas, 5 de los cuales son medidos por primera vez. Hemos comparado nuestras medidas con predicciones teóricas obteniendo una concordancia excelente. Hemos sido capaces de medir el término relativista con suficiente precisión para testar la relatividad general con este método por primera vez.
The detection of the first binary star more than 200 years ago opened the door to a whole new field of astrophysics research, devoted to the study of their evolution and mutual interactions employing the analysis of the reflex motion caused by the orbiting companion. It was therefore only a matter of time that the development of astronomical instrumentation reached a precise enough level to detect the motions induced by planetary companions over their host stars. The discovery of the first exoplanet a few decades ago prompted a rapid surge of surveys dedicated to their search, which are providing a huge amount of data that can be also used to study the properties of stars. The main purpose of this thesis is the study and characterization of exoplanets, stars, and stellar systems by analyzing data from high-precision spectroscopic and photometric exoplanet surveys. This is for instance the case of the CARMENES and TESS projects, which aim at the discovery of such objects by means of the radial velocity imprinted on their host star or by the detection of transits, respectively, with particular emphasis on low-mass M-dwarf stars. Firstly, we developed a novel approach to constraint the properties of starspots and convective motions on M dwarfs by using the variability induced by stellar activity. In particular, we modeled chromatic radial velocities and photometric time series of the M-dwarf star YZ CMi using the stellar activity model code StarSim. The results of our analysis revealed the presence of a large polar spot with a temperature 200 K lower than that of the surrounding photosphere, and found that the convective shift of this star may be reversed toward redshift. Based on a combined analysis of CARMENES and archival radial velocities, we present in this thesis the detection of a mini-Neptune and a super-Earth around the M-dwarf stars LSPM J2116+0234 and GJ 686, respectively, just outside the inner edge of their habitable zones. To avoid determining biased parameters due to the contamination from stellar activity, the planetary signals were jointly modeled with a correlated noise model describing stellar variability. The derived orbital parameters resulted in orbital periods of 14.45 d and 15.53 d, and minimum masses of 12.8 and 6.6 Earth masses for LSPM J2116+0234b and GJ 686b, respectively. The radial velocity method used to detect exoplanets with CARMENES is also yielding multiple stellar systems as a by-product. In this work, we report on the discovery of 17 new multiple systems, for which we determined their spectroscopic orbits. The sample is composed of 15 binary systems (5 with undetected companions) and 2 triple systems. We determined that the unseen companions of two of the binaries have minimum masses compatible with a brown dwarf, and we demonstrated that one of the systems is an M-dwarf--white dwarf binary. We also found one of the youngest binary systems with measured masses by analysing both radial velocities and astrometric measurements. Finally, we used TESS photometry to derive eclipse timings for 16 well-studied eccentric eclipsing binaries. We analyzed the change in the difference between primary and secondary eclipse timings over time to determine the apsidal motion rate of 10 of the systems in the sample, 5 of which are measured for the first time. We compared the measured values with theoretical predictions, obtaining an excellent agreement. We were able to measure the general relativistic.
Universitat Autònoma de Barcelona. Programa de Doctorat en Física

Després del descobriment dels primers exoplanetes fa unes tres dècades, la detecció i caracterització de companys planetaris s’ha convertit en un tema de recerca prominent, especialment la cerca de planetes semblants a la Terra, cossos rocosos que orbiten a la zona habitable (HZ) de les seves estrelles hostes. Un dels principals mètodes utilitzats per trobar i caracteritzar exoplanetes és la tècnica de l’espectroscòpia Doppler o velocitat radial (RV), basada en l’ús d’espectres estel·lars per mesurar canvis periòdics en la RV d’una estrella causats per l’atracció gravitatòria d’un exoplaneta en òrbita. Actualment, la variabilitat intrínseca de les estrelles hostes és el principal repte en l’estudi d’exoplanetes. Les estrelles no són cossos invariables i homogenis, sinó que presenten variabilitat en diferents escales de temps. La més rellevant és l’activitat magnètica estel·lar, que inclou fenòmens com ara taques o fàcules que apareixen a la superfície de l’estrella i estan modulades per la seva rotació. Aquests fenòmens distorsionen els espectres estel·lars, introduint biaixos en les RVs prou grans com per amagar o fins i tot imitar el senyal causat per un planeta. Per tant, per continuar detectant i estudiant exoplanetes de baixa massa, és clau aconseguir una millor comprensió d’aquests fenòmens estel·lars i els seus efectes en les nostres observacions. Aquesta tesi se centra en l’estudi dels efectes de l’activitat estel·lar en observacions espectroscòpiques d’estrelles fredes obtingudes amb l’instrument CARMENES. CARMENES és un espectrògraf d’alta resolució capaç d’observar el rang de longitud d’ona visible i infraroig proper. Està realitzant un estudi de més de 300 nanes M, les estrelles amb menor massa de la seqüència principal, amb l’objectiu primordial de detectar exoplanetes petits. En primer lloc, hem desenvolupat un codi que implementa el mètode de la funció de correlació creuada (CCF) per mesurar RVs i indicadors d’activitat estel·lar en observacions d’alta resolució, i l’hem aplicat a les dades de CARMENES. Aquest mètode utilitza màscares binàries ponderades, un template estel·lar simplificat construït mitjançant la selecció de línies espectrals. Hem creat diverses màscares en funció del subtipus espectral i de la velocitat de rotació de l’estrella a analitzar. A continuació, hem utilitzat els indicadors d’activitat derivats de la CCF, juntament amb altres indicadors d’activitat espectroscòpics, per analitzar les seves variacions temporals en una mostra de quasi 100 nanes M de diverses masses i nivells d’activitat. Aproximadament la meitat de les estrelles analitzades mostren RVs amb senyals d’activitat clars. Diferents indicadors són sensibles a l’activitat de manera diferent segons les característiques de l’estrella: indicadors cromosfèrics són més útils per a estrelles de baixa activitat, indicadors relacionats amb el canvi de RV amb longitud d’ona funcionen millor per a les estrelles més actives, i altres indicadors relacionats amb el canvi d’amplada de les línies fotosfèriques proporcionen resultats similars en tot tipus d’estrelles, però són especialment útils per a les més actives i de menor massa. Finalment, hem analitzat els efectes de l’activitat sobre línies d’absorció individuals presents en l’espectre d’estrelles actives. Estudiant les correlacions entre les RVs de línies individuals i els indicadors d’activitat, podem classificar les línies observades segons la seva sensibilitat a l’activitat. Això ens permet seleccionar línies afectades de forma diferent per l’activitat i utilitzar-les per tornar a calcular RVs. Així obtenim RVs per a les quals mitiguem o incrementem el senyal d’activitat en diversos graus. També observem que les mateixes línies en diferents estrelles mostren diferent sensibilitat a l’activitat.
Después del descubrimiento de los primeros exoplanetas hace unas tres décadas, la detección y caracterización de compañeros planetarios se ha convertido en un tema de investigación prominente, especialmente la búsqueda de planetas parecidos a la Tierra, cuerpos rocosos que orbitan en la zona habitable (HZ) de sus estrellas huéspedes. Uno de los principales métodos utilizados para encontrar y caracterizar exoplanetas es la técnica de la espectroscopía Doppler o velocidad radial (RV), basada en el uso de espectros estelares para medir cambios periódicos en la RV de una estrella causados por la atracción gravitatoria de un exoplaneta en órbita. Actualmente, la variabilidad intrínseca de las estrellas huéspedes es el principal reto en el estudio de exoplanetas. Las estrellas no son cuerpos invariables ni homogéneos, sino que presentan variabilidad en distintas escalas de tiempo. La más relevante es la actividad magnética estelar, que incluye fenómenos como manchas o fáculas que aparecen en la superficie de la estrella y están moduladas por su rotación. Estos fenómenos distorsionan los espectros estelares, introduciendo sesgos en las RVs suficientemente grandes como para esconder o hasta imitar la señal causada por un planeta. Por lo tanto, para continuar detectando y estudiando exoplanetas de baja masa, una mejor comprensión de estos fenómenos estelares y sus efectos en nuestras observaciones es clave. Esta tesis se centra en el estudio de los efectos de la actividad estelar en observaciones espectroscópicas de estrellas frías obtenidas con el instrumento CARMENES. CARMENES es un espectrógrafo de alta resolución capaz de observar en el rango de longitudes de onda visible e infrarojo cercano. Está realizando un estudio de más de 300 enanas M, las estrellas con menor masa de la secuencia principal, con el objetivo primordial de detectar exoplanetas pequeños. En primer lugar, hemos desarrollado un código que implementa el método de la función de correlación cruzada (CCF) para medir RVs e indicadores de actividad estelar en observaciones de alta resolución, y lo hemos aplicado a los datos de CARMENES. Este método usa máscaras binarias ponderadas, un template estelar simplificado construido seleccionando líneas espectrales. Hemos creado varias máscaras en función del subtipo espectral y de la velocidad de rotación de la estrella a analizar. A continuación, hemos utilizado los indicadores de actividad derivados de la CCF, juntamente con otros indicadores de actividad espectroscópicos, para analizar sus variaciones temporales en una muestra de casi 100 enanas M de varias masas y niveles de actividad. Aproximadamente la mitad de las estrellas analizadas muestran RVs con señales de actividad claros. Distintos indicadores son sensibles a la actividad de forma diferente según las características de la estrella: indicadores cromosféricos son más útiles para estrellas de baja actividad, indicadores relacionados con el cambio de RV con la longitud de onda funcionan mejor para estrellas más activas, y otros indicadores relacionados con el cambio de anchura de las líneas fotosféricas proporcionan resultados similares en todo tipo de estrellas, pero son especialmente útiles para las más activas y de menor masa. Finalmente, hemos analizado los efectos de la actividad sobre líneas de absorción individuales presentes en el espectro de estrellas activas. Estudiando las correlaciones entre las RVs de líneas individuales y los indicadores de actividad, podemos clasificar las líneas observadas según su sensibilidad a la actividad. Esto nos permite seleccionar líneas afectadas de forma distinta por la actividad y usarlas para volver a calcular RVs. De esta forma obtenemos RVs para las cuales mitigamos o incrementamos la señal de actividad en diversos grados. También observamos que las mismas líneas en distintas estrellas muestran diferente sensibilidad a la actividad.
After the discovery of the first exoplanets about three decades ago, the detection and characterization of planetary companions has become a prominent research topic, especially the search for Earth-like planets, rocky bodies orbiting in the habitable zone (HZ) of their host stars. One of the main methods used to find and characterise exoplanets is the Doppler spectroscopy or radial velocity (RV) technique, based on using stellar spectra to measure periodic changes in the RV of a star caused by the gravitational pull of an orbiting exoplanet. Currently, the intrinsic variability of the host stars is the major challenge faced in the study of exoplanets. Stars are not quiet, homogeneous bodies, but display variability on different timescales, the most concerning being stellar magnetic activity, phenomena such as spots or faculae appearing on the stellar surface and modulated by the stellar rotation. These features distort the stellar spectra, introducing biases in our RVs that can be large enough to hide or even mimic the signal caused by a planet. Therefore, to continue detecting and studying low-mass exoplanets, a better understanding of these stellar phenomena and their effects on our observations is key. This thesis is focused on the study of stellar activity effects on spectroscopic observations of cool stars obtained with the CARMENES instrument. CARMENES is a high-resolution spectrograph capable of observing on the visible and near-infrared wavelength ranges. It is performing a survey of over 300 M dwarfs, stars at the low-mass end of the main sequence, with the main goal of detecting small exoplanets. Firstly, we developed a pipeline that implements the cross-correlation function (CCF) method to measure RVs and indicators of stellar activity on high-resolution observations, and applied it to the CARMENES survey data. This method uses weighted binary masks, a simplified stellar template built by selecting sharp spectral lines, of which we created different kinds depending on the spectral subtype and the rotational velocity of the target star. We then used the activity indicators derived from the CCF, together with other spectroscopic activity proxies, to analyse their temporal variations in a sample of almost 100 M dwarfs with a range of masses and activity levels. We found that about half of the stars analysed show RVs with clear signals of activity. Different indicators trace activity differently depending on the characteristics of the star: chromospheric indicators are the most useful for low-activity stars, indicators related to the change in RV with wavelength work better for the most active stars, and other indicators related to the change in width of the photospheric lines provide similar results in all types of stars, but are especially useful for the most active and lowest-mass ones. Finally, we analysed the effects of activity on individual absorption features present on the spectra of active stars. By studying the correlations between the individual line RVs and activity indicators, we are able to classify the observed lines according to their sensitivity to activity. This allow us to select differently affected lines and use them to recompute RVs for which we mitigate or enhance the activity signal to varying degrees. We also observe that the same lines on different stars show different sensitivities to activity.

The field of exoplanetology has evolved significantly from its beginnings in the 1990s, gradually shifting emphasis from the detection of new exoplanets to characterisation of those already discovered. Simultaneously, considerable progress has been made in the area of automatisation of both instruments and data reduction techniques, leading to an ever-growing influx of new data, discoveries and facts about the planets outside of the Solar System. Observations of transiting exoplanets can be divided into two major themes: surveys, designed to find new planetary candidates; and follow-up observations, which offer a chance to learn more about the characteristics of the previously identified candidates and confirm their planetary nature. In this thesis, I introduce both aspects in the context of the current exoplanetary re- search, and go on to describe in considerable detail the objects of two observational follow-up projects, planets WASP-12 band KIC 12557548 b, together with a selection of new techniques I develop to assist in data reduction and analysis of large photometric datasets. In the WASP-12 b study, I use ULTRACAM on the William Rerschel Telescope to search in the visible light for the presence of the early ingress signature, observed previously with the Rubble Space Telescope in the near-ultraviolet. I also investigate claims of a transit timing variation in this system. I use the same instruments to carry out KIC 12557548 b observations, with the aim to measure the colour dependence of the extinction and scattering due to the dust in the tail of the putative planet and provide direct evidence in favour of this object being a disrupting low-mass rocky planet, feeding a transiting dust cloud. I also present a new algorithm used to correct for scattered light in astronomical images, ULTRACorrect, and introduce a bespoke photometry pipeline, ULTRAPhoto, together with a selection of other methods useful in observations planning and data analysis

This thesis provides a multi-pronged approach towards paving the way for future space and ground based exoplanet characterisation e↵orts as well as providing new analysis of the atmosphere of the exoplanet HD 179949 b. This is done, firstly, by outlining engineering trade studies conducted for the attitude and orbit control system (AOCS) and sun shield for the Exoplanet Characterisation Observatory (EChO) spacecraft (a proposed European Space Agency exoplanet space mission). These trade studies were conducted in collaboration with EADS Astrium. A cold gas system with the possibility of a hybrid system which would include the use of reaction wheels is recommend for the design of the AOCS. For the sun shield, a V-groove cone shield is concluded to provide the best thermal coverage while also providing stay light protection as well as being more mechanically symmetric than other options. Simulations are then conducted to determine the number of transiting planets future surveys should expect to find around stars within 50 parsecs of the sun. This is done by taking the known stars within 50 parsecs and adding a simulated planet population based on current models and observations to each star. Assumptions are made regarding observability of a planetary transit and a Monte Carlo simulation run to gain statistics on the number and type of planetary systems that can be expected to be found. The results of the simulation show a mean expected number of 27 detectable transiting planets within 50 parsecs. Next, using the Position and Proper Motion Extended-L (PPMXL) catalogue, optical and near-infrared colour cuts were used together with a reduced proper motion cut to find bright M dwarfs for future exoplanet transit studies. PPMXL’s low proper motion uncertainties allow this work to probe down to smaller proper motions than previous similar studies. Unique objects found with this method were combined with that of previous work to produce 8479 K < 9 M dwarfs. Low-resolution spectroscopy was obtained of a sample of the objects found using this selection method to gain statistics on their spectral type and physical properties. Results show a spectral-type range of K7-M4V. This catalogue is the most complete collection of K < 9 M dwarfs currently available and is made available here. High resolution spectroscopy and model spectra of planetary atmospheres is then used along with a spectral deconvolution technique to attempt to detect the Doppler shifted signal of the non-transiting planet HD 179949 b. The signal was not detected but new upper limits were set ruling out the presence of TiO down to a log10 ✏0 = -4.09 with 99.9 per cent confidence. Simulations conducted by this work imply a loss of sensitivity occurring possibly due to varying telluric interference or instrumental systematics.

The search for extrasolar planets had been ongoing for many years when Mayorand Queloz discovered 51 Pegasi b in 1995. It was a giant gas planet similar to Jupiter, but with a larger radius and of only half of Jupiter’s mass. Theso called Hot Jupiter was observed to orbit its host star 7 times closer thanMercury is orbiting the Sun. Theoretical models at the time stated that gasgiants could not form in such a short distance to the host star. Thus, thisdiscovery was completely unexpected. It was the beginning of a new field ofresearch where the diversity of exoplanets is the most remarkable discovery, challenging theoretical models. Thanks to the Kepler space telescope and anew generation of space missions such as TESS, thousands of exoplanets havebeen discovered and thousands of planet candidates await confirmation. In this thesis I have studied all confirmed exoplanets to this date, which havebeen discovered by the radial velocity and/or the transit method. The planetparameters and their stellar hosts are available on NASA’s Exoplanet Archive.For all planets < 100 M⊕, I have assessed and updated the parameters for eachplanet in particular when several solutions exist. There are several types ofplanets, but the focus of this work are small planets which come in two sizes: Rocky super-Earths, and the slightly larger and lower density sub-Neptune. Different types of planets have different radii and mass ranges, which togetherwith composition and interior structure are separating the types from each other. These mass and radii ranges are however not universally defined, and in thisreport the super-Earth and sub-Neptune ranges are discussed together with their typical characteristics. The radii and mass ranges of the two different classes of small planets are overlapping and are often difficult to classify. In particularfor planets in between 2 R⊕ and 3 R⊕, there is an ambiguity of structure and composition. This report will also investigate how planet properties depend on the stellarhost properties and on the orbital distances to the stars. One of my mainresults is that sub-Neptunes are common orbiting host stars with low metallicity, in contrast to super-Earths which are common orbiting host stars with highmetallicity. Other parameters, such as stellar effective temperature, seem to have no influence on planet properties. Super-Earth’s are found at a wide range of orbital distances while the sub-Neptunes cluster in a narrow range of orbital distances to their host star. Sub-Neptunes have an atmosphere, and are orbiting at distances where the atmosphere does not evaporate from intense host star radiation. If an atmospheree vaporates, only the rocky core of the planet is left. Thus, some super-Earths might have been sub-Neptunes that have lost their atmospheres. My second main result is that planets with characteristics of sub-Neptunes (with respect to density and interior structure) of 10 M⊕ to 15 M⊕ have radiibetween 2 R⊕ and 4.5 R⊕. Sub-Neptunes in the upper mass limit, between 15M⊕ to 17 M⊕, have radii from 2.6 R⊕ to 7.5 R⊕. And finally, my third result is the relation between planet density and equilibrium temperature. The density of all planets with masses < 15 M⊕ is Earth-like for equilibrium temperatures > 1400 K. For lower equilibrium temperatures corresponding to longer orbital periods, or lower-mass and cooler stars, planetswith masses < 15 M⊕ have a larger spread in densities. However, it never fallsbelow a diagonal linear trend in the density against equilibrium temperature diagram described by ρ = 2.6 × log10(Teq) − 7.46.

In the last decade, over a million stars were monitored to detect transiting planets. Manual interpretation of potential exoplanet candidates is labour intensive and subject to human error, the results of which are difficult to quantify. Here we present a new method of detecting exoplanet candidates in large planetary search projects that, unlike current methods, uses a neural network. Neural networks, also called 'deep learning' or 'deep nets', are designed to give a computer perception into a specific problem by training it to recognize patterns. Unlike past transit detection algorithms, deep nets learn to recognize planet features instead of relying on hand-coded metrics that humans perceive as the most representative. Our convolutional neural network is capable of detecting Earth-like exoplanets in noisy time series data with a greater accuracy than a least-squares method. Deep nets are highly generalizable allowing data to be evaluated from different time series after interpolation without compromising performance. As validated by our deep net analysis of Kepler light curves, we detect periodic transits consistent with the true period without any model fitting. Our study indicates that machine learning will facilitate the characterization of exoplanets in future analysis of large astronomy data sets.

Lightning is an important electrical phenomenon, known to exist in several Solar System planets. Amongst others, it carries information on convection and cloud formation, and may be important for pre-biotic chemistry. Exoplanets and brown dwarfs have been shown to host environments appropriate for the initiation of lightning discharges. In this PhD project, I aim to determine if lightning on exoplanets and brown dwarfs can be more energetic than it is known from Solar System planets, what are the most promising signatures to look for, and if these "exo-lightning" signatures can be detected from Earth. This thesis focuses on three major topics. First I discuss a lightning climatology study of Earth, Jupiter, Saturn, and Venus. I apply the obtained lightning statistics to extrasolar planets in order to give a first estimate on lightning occurrence on exoplanets and brown dwarfs. Next, I introduce a short study of potential lightning activity on the exoplanet HAT-P-11b, based on previous radio observations. Related to this, I discuss a first estimate of observability of lightning from close brown dwarfs, with the optical Danish Telescope. The final part of my project focuses on a lightning radio model, which is applied to study the energy and radio power released from lightning discharges in hot giant gas planetary and brown dwarf atmospheres. The released energy determines the observability of signatures, and the effect lightning has on the local atmosphere of the object. This work combines knowledge obtained from planetary and earth sciences and uses that to learn more about extrasolar systems. My main results show that lightning on exoplanets may be more energetic than in the Solar System, supporting the possibility of future observations and detection of lightning activity on an extrasolar body. My work provides the base for future radio, optical, and infrared search for "exo-lightning".

The field of extrasolar planets is undoubtedly one of the most exciting and fast-moving in astronomy. Thanks to the Kepler Space Telescope, which has given us the Kepler and K2 missions, we now have thousands of planets to study and thousands more candidates waiting to be confirmed.For this thesis work, I used K2 data in the form of stellar light curves for Campaign 15 – the 15th observation field of this mission – to search for transiting exoplanets. I present one way to produce a viable list of planetary candidates, which is the first step to exoplanet discovery. I do this by first applying a package of subroutines called EXOTRANS to the light curves. EXOTRANS uses two wavelet-based filter routines: VARLET and PHALET. VARLET is used to remove stellar variability and abrupt discontinuities in the light curve. Since a transit appears box-like, EXOTRANS utilises a box-fitting least-squares algorithm to extract the transit event by fitting a square box. PHALET removes disturbances of known frequencies (and their harmonics) and is used to search the light curve for additional planets. Once EXOTRANS finishes its run, I examine the resulting plots and flag the ones, which contain a transit feature that does not appear to be a false positive. I then perform calculations on the shortlisted candidates to further refine their quality. This resulted in a list of 30 exoplanet candidates. Finally, for eight of them, I used a light curve detrending routine (Exotrending) and another software package, Pyaneti, for transit data fitting. Pyaneti uses MCMC sampling with a Bayesian approach to derive the most accurate orbital and candidate parameters. Based on these estimates and combined with stellar parameters from the Ecliptic Plane Input Catalogue, I comment on the eight candidates and their host stars.However, these comments are only preliminary and speculative until follow-up investigation has been conducted. The most widely used method to do this is the radial velocity method, through which more detailed information is obtained about the host star and in turn, about the candidate. This information, specifically the planetary mass, allows for the bulk density to be estimated, which can give indication about a planet’s composition.Although the Kepler Space Telescope is at the end of its life, new missions with at least a partial focus on exoplanets, are either ongoing (Transiting Exoplanets Survey Satellite – TESS) or upcoming (Characterising Exoplanets Satellite – CHEOPS, James Webb Space Telescope – JWST, Planetary Transits and Oscillations – PLATO). They will add thousands of new planets, providing unprecedented accuracy on the transit parameters and will make significant advances in the field of exoplanet characterisation. The methods used in this work are as applicable to these missions as they have been for the now retired Convection, Rotation et Transits planétaires (CoRoT) – the first space mission dedicated to exoplanet research, and Kepler.

Circumbinary planets are bodies that orbit both components in a binary star system. This thesis focuses on transits of these planets, which with the aid of the Kepler space telescope have recently led to the discovery of several such objects. First, transit timing variations - departures from strict periodicity in the transit times - are studied. These arise from both the motion of the host stars and relatively rapid precession of the planet’s orbit. Limits on the maximum possible transit timing variation are derived, and tested against N-body simulations of simulated circumbinary systems. These limits are then utilised to form a search algorithm designed to find these planets in light curves, focusing on data from the WASP and Kepler observatories. This search algorithm uses an individual transit search to identify potential transit signatures, then forms periodograms allowing for the possible timing variations. It is used to identify several new candidate planets, as well as confirm detections of previously known circumbinary systems. In addition a number of interesting multiple stellar systems are identified including the as yet unexplained KIC2856960, which display multiple eclipses, significant tidal heating or rapid orbital evolution on the timescale of the 4 year Kepler observations. In 2013 unbiased stellar radii for the eclipsing binaries of the Kepler dataset were not available. A catalogue is produced, derived from spectral energy distribution fits to data from the KIS, HES and 2MASS surveys of the Kepler field, which gives temperatures for these stars accurate to ~300K. These are then used to find calibrated stellar masses and radii. These parameters, in combination with the search algorithm, are used to study circumbinary planet rates of occurrence in the Kepler dataset. The known sample of eclipsing binaries is tested for detectability, and a Monte Carlo population synthesis used to find probability density functions for these rates. These are a function of the as yet unknown circumbinary planetary inclination distribution, and show that the rate of occurrence of circumbinary planets is consistent with that of single stars if these planets are in the majority coplanar with their host binaries. However, if they are more misaligned, to a degree greater than that implied by a 5° Gaussian distribution, their rate of occurrence becomes significantly higher. Furthermore, it is confirmed that planets of Jupiter size and greater occur less often in circumbinary configurations, and that circumbinary planets are preferentially found around binaries with periods longer than ~7 days.

This report describes simulations of observations with the near-infrared high-resolution spectrometer SIMPLE that is proposed to the ESO telescope E-ELT. We simulate M4 and G2 stars with transiting Earth-like planets and the goal is to distinguish spectral features originating from the atmosphere of the exoplanet. Noise levels of different magnitudes are added to the simulations and the minimal signal-to-noise required for detection of the atmosphere is estimated. Our conclusion is that detection of atmospheric features looks promising using this setup.

La méthode des vitesses radiales a été la première méthode de détection d'une exoplanète. Depuis 1995, elle a permis de découvrir plus de 2000 exoplanètes et la méthode des RV a ses avantages. Outre la découverte de nouvelles exoplanètes et la détermination de leur masse apparente, elle est utilisée pour confirmer les exoplanètes découvertes par d'autres méthodes et pour mesurer la masse des exoplanètes en transit. Cependant, la méthode RV est limitée par les capacités techniques: la taille et la disponibilité du télescope, la stabilité et la précision de l'étalonnage de la longueur d'onde du spectrographe. Les spectrographes de nouvelle génération sont extrêmement précis d'un point de vue instrumental, ils sont stables et parfaitement calibrés, mais leur précision n'est pas encore suffisante pour détecter une exoplanète jumelle de la Terre. Ainsi, toute amélioration du traitement associé à l'extraction de la RV devrait se traduire par une amélioration de la précision, ou par une réduction du temps de télescope nécessaire pour atteindre une précision définie.Les spectres utilisés pour la méthode des RV étant obtenus à partir de la surface de la Terre, ils contiennent le spectre de l'étoile et le spectre de l'atmosphère terrestre (absorption tellurique). Jusqu'à récemment, les régions spectrales contaminées par l'absorption tellurique étaient exclues du traitement. Après correction, ces régions deviennent disponibles pour être utilisées pour la récupération de RV, améliorant ainsi la précision sur RV. Thèse est consacrée au développement de l'algorithme de correction (basé sur le service web TAPAS), et à l'estimation de l'augmentation de la précision des mesures de RV due à l'augmentation de la gamme de longueurs d'onde disponibles. La méthode de correction a été développée pour l'absorption tellurique causée par O2 et H2O dans le domaine des longueurs d'onde visibles et testée sur les données ouvertes d'ESPRESSO. Pour notre étude de cas de l'étoile HD40307, l'erreur formelle sur la RV est réduite de 0.77 à 0.64 ms-1, ce qui correspond à une économie significative de 45% de temps de télescope.En plus du travail sur la correction de l'absorption tellurique, la thèse se concentre également sur le calcul direct de la RV. 2 méthodes principales existent et sont largement utilisées: la méthode de la fonction de corrélation croisée (CCF) et la méthode du template matching. Il existe également la méthode de Pierre Connes (décrite dans Absolute Astronomical Accelerometry), qui a ses limites en raison de son incapacité à s'appliquer à de grandes variations de vitesse. Dans la thèse, nous proposons et montrons l'application d'une nouvelle méthode, qui est une combinaison de la méthode classique de la CCF et de la méthode de Pierre Connes (PC). Nous proposons d'utiliser la méthode PC pour calculer le changement de RV directement sur la CCF, avec une correction préalable pour le BERV, au lieu de l'ajustement gaussien de la CCF. La méthode a été testée pour les données d'une étoile avec un système planétaire et sans système planétaire, les résultats montrent que la précision du calcul de la RV en utilisant la méthode PC est plus élevée que celle de l'ajustement gaussien. La thèse montre également les débuts d'une correction de l'activité stellaire, basée sur la méthode PC.La deuxième partie de la thèse est consacrée au développement d'un modèle de spectroscopie en transmission pour les exoplanètes telluriques en début de formation. Le développement d'un modèle est particulièrement pertinent après le lancement du JWST et en prévision du lancement d'Ariel, car la plupart des modèles actuels se concentrent davantage sur les géantes gazeuses et les naines brunes. Un modèle d'absorption raie par raie à haute résolution a été développé pour une atmosphère composée de vapeur d'eau H2O et de CO2
The radial velocity method was the first method to detect an exoplanet. Since 1995 it has discovered more than 2000 more exoplanets and, although the transit photometry method is currently the most productive, the radial velocity method has its advantages. In addition to being able to discover new exoplanets and determine their apparent mass msini it is used to confirm exoplanets found by other methods and measure the mass of transit exoplanets. However, the RV method is limited by technical capabilities: the size and availability of the telescope, the stability and accuracy of the wavelength calibration of the spectrograph. New generation spectrographs are extremely accurate from an instrumental point of view, they are stable and perfectly calibrated, but their accuracy is still not enough to detect Earth's exoplanet twin. If it is not possible to improve the instrument the data processing needs to be refined, so any improvement of the processing associated to the radial velocity retrieval should result in an improvement of precision, or in a shorter telescope time required to achieve a defined-goal precision.Because the spectra for the radial velocity method are obtained from the Earth's surface, they contain the spectrum of the star and the spectrum of the Earth's atmosphere (telluric absorption). Until recently, spectral regions contaminated by telluric absorption were excluded from consideration. After telluric correction, those regions become available to be used for RV retrieval, improving the precision on RV.This thesis is devoted to the development of telluric correction algorithm (based on TAPAS web service), describing the telluric correction method and estimating an increase in the precision of radial velocity measurements due to increased available wavelength range. The correction method was developed for telluric absorption caused by O2 and H2O in the visible wavelength range and probed on ESPRESSO open data. For our case study of star HD40307, the formal error on RV is reduced from 0.77 to 0.64 ms-1, corresponding to a significant saving of 45% telescope time.In addition to work on the telluric absorption correction, the thesis also focuses on the direct calculation of the radial velocity. At the moment, there are 2 main methods that exist and are widely used: the cross-correlation function (CCF) method and the template matching method. There is also the Pierre Connes method (described at Absolute Astronomical Accelerometry), which has its limitations due to its inability to be applied to large velocity variations. In this thesis we propose and show the application of a new method, which is a combination of the classical method of cross-correlation function and the method of Pierre Connes (PC). We propose to use the PC method of calculating the change of radial velocity directly on the CCF, with prior correction for BERV, instead of the classical Gaussian fitting of the CCF.The method has been tested for data of a star with a planetary system as well as without a planetary system, the results show that the precision of the radial velocity calculation using the PC method is higher than that of the Gaussian fit. The thesis also shows the beginnings of a stellar activity correction, based on the PC method. As the CCF can be considered an averaged stellar line, counting the change in radial velocity for the left and right wings separately, stellar activity can be analysed.The second part of the thesis is dedicated to the development of a transmission spectroscopy model for telluric exoplanets at the beginning of formation. The development of such a model is particularly relevant after the JWST launch and in anticipation of the Ariel launch, as most current models focus more on gas giants and brown dwarfs. A high-resolution line-by-line model has been developed for an atmosphere consisting of H2O vapour and CO2

The only way to measure the diameter of a planet outside the Solar System is if it transits its host star. Transit data combined with radial velocity (RV) data give an exoplanet's mass. Mass and volume yield density, so transits give unique insights into the interior structure of an exoplanet. Super-Earths are a class of exoplanet with masses a few times that of Earth, for which no examples exist in our Solar System. The goals of this thesis: to detect and characterise transits of exoplanets (particularly super-Earths) discovered via RV surveys orbiting bright stars. The observational tool: MOST (Microvariability & Oscillations of STars) - a microsatellite housing an optical telescope which can monitor stars with high precision. We searched 12 super-Earth candidate systems, applying special data reduction and analysis techniques. The search gives upper limits on the transit depths of 11 of the planets. For GJ 581e (innermost planet of an M dwarf system), the 1σ upper limit excludes most transiting configurations for a planet with water ice or H/He compositions. MOST data of HD 97658 rejected a claim of a transit detection in this system. The timely MOST rejection cancelled observatory programmes dedicated to follow up on the transit claim, preventing the waste of valuable time on major facilities. In parallel with the MOST survey, we analysed a decade of ground-based photometry to exclude most transiting configurations for the massive exoplanet HD 192263b. We showed that the star's rotation period does not coincide with the planet's orbital period, as was previously reported. We also find evidence for an 8-year activity cycle in the host star. The twelfth star in the MOST survey is 55 Cancri, whose innermost planet (55 Cnc e) has an orbital period of less than a day and transits the star. We present 42 days of new MOST photometry of this system, and derive one of the most precise radius values (1.99 ± 0.08 Earth radii) known for any super-Earth. We explore the possibility of star-exoplanet interaction, and set a limit on the albedo (reflectivity) of the planet, which has implications for its atmospheric composition.

To date nearly 300 exoplanets have been discovered, most of them through measurements of the wobble induced by the planet in the motion of its host star. We have developed a program, based on Bayesian inference, to fit eccentric Keplerian orbits to exoplanet radial velocity data. The data consist of optical spectra obtained using the HIRES echelle spectrometer on the Keck I telescope. We have applied the program to 58 sets of measurements. We have obtained probability distributions for the orbital period and eccentricity for each set. We have found that clear upper and lower limits can be placed on the period while the eccentricity proves more difficult to constrain. From the average period probability distribution we prepared, we preliminarily concluded that there is a much higher probability to find exoplanets with periods below 10000 days than with periods above 10000 days. We also suspect the existence of a correlation between the period and the eccentricity, as well as that of a possible trend of decreasing period with increasing stellar metallicity.
À date presque 300 exoplanètes ont été découvertes, la plupart à travers des mesures du vacillement provoqué par la planète dans le mouvement de son étoile mère. Nous avons mis au point un programme, basé sur l'inférence bayésienne, pour modéliser des données de vélocité radiale pour la recherche d'exoplanètes par des orbites excentriques képlériennes. Les données sont des spectres optiques et ont été recueillies avec le spectromètre échelle HIRES au télescope Keck I. Nous avons utilisé le programme pour analyser 58 ensembles de données. Nous avons obtenu des distributions de probabilité pour la période orbitale ainsi que pour l'excentricité pour chaque ensemble. Nous avons trouvé qu'il est possible de placer des limites supérieures et inférieures sur la période, mais que l'excentricité est plus difficile à contraindre. À partir de la moyenne des distributions de probabilité que nous avons obtenu pour la période, nous avons préliminairement conclu qu'il y a une beaucoup plus grande probabilité de trouver des exoplanètes avec des périodes inférieures à 10000 jours qu'avec des périodes supérieures à 10000 jours. Nous suspectons la présence d'une corrélation entre la période et l'excentricité, ainsi qu'une possible tendance de la période à décroître à mesure que la métallicité stellaire augmente.

Understanding the interior structures and chemistry of Earth-like exoplanets is crucial for us to characterize exoplanets, and to find potentially habitable planets. First, I provide a model grid of the mass-radius relations for solid planets in between 0.1 and 100 Earth masses. Planets are modeled as consisting of three layers: Fe, MgSiO3 and H2O. This model is made into an interactive tool available online: http://www.astrozeng.com/ Second, I explore the effects of thermal evolution and phase transitions on the interior structures of H2O-rich planets. It is shown that the bulk H2O in such planets may exist in the plasma, superionic, ionic, Ice VII, or Ice X states depending on sizes, ages, and cooling rates. The results suggest that super-Earth sized planets which are not significantly irradiated by parent stars and which are older than approximately 3 billion years, are mostly solid. Third, I describe a new, semi-empirical mass-radius relation for solid exoplanets. It is based on the recent mass and radius measurements of 5 exoplanets within 1 to 10 Earth masses and an extrapolation of the seismically derived pressure-density relation of the Earth's interior (PREM). The implication of common core mass fractions of 0.2~0.3 among these solid exoplanets is also discussed. Fourth, I model the elemental abundance patterns of solid exoplanets based on that of their host stars. This model is constructed from the following steps of planet formation: volatile depletion, core formation, and late delivery. This model could provide constraints on the chemical compositions of solid exoplanets in addition to the constraints derived from their masses and radii. In terms of future directions of this research, I hope to link my chemical model of solid exoplanets with the chemical evolution model of our galaxy, such as the one being developed by the Lars Hernquist group, which may indicate a different mineralogy of solid exoplanets formed at different ages of our galaxy, as well as the implications for the habitability of these planets. I also hope to understand the origins of the volatile contents on the surfaces of solid planets, which are important prerequisites for possible origins of life on them.
Astronomy

Photometric transit surveys on the ground & in space have detected thousands of transiting exoplanets, typically by analytically combining the signals from multiple transits. This technique of exoplanet detection was exploited in K2 to detect nearly 200 candidate planets, and extensive follow-up was able to confirm the planet K2-110b as a 2:6 0:1R , 16:7 3:2M planet on a 14d orbit around a K-dwarf. The ability to push beyond the time limit set by transit surveys to detect long-period transiting objects from a single eclipse was also studied. This was performed by developing a search technique to search for planets around bright stars in WASP and NGTS photometry, finding NGTS to be marginally better than WASP at detecting such planets with 4:14 0:16 per year compared to 1:43 0:15, and detecting many planet candidates for which follow-up is on-going. This search was then adapted to search for deep, long-duration eclipses in all WASP targets. The results of this survey are described in this thesis, as well as detailed results for the candidate PDS-110, a young T-Tauri star which exhibited 20d-long, 30%- deep eclipses in 2008 and 2011. Space-based photometers such as Kepler have the precision to identify small exoplanets and eclipsing binary candidates from only a single eclipse. K2, with its 75d campaign duration and high-precision photometry, is not only ideally suited to detect significant numbers of single-eclipsing objects, but also to characterise them from a single event. The Bayesian transit-fitting tool ("Namaste: An MCMC Analysis of Single Transit Exoplanets") was developed to extract planetary and orbital information from single transits, and was applied to 71 candidate events detected in K2 photometry. The techniques developed in this thesis are highly applicable to future transit surveys such as TESS & PLATO, which will be able to discover & characterise large numbers of long period planets in this way.

La photométrie des transits permet de détecter des planètes extrasolaires en mesurant leur rayon. Dans cet objectif, le télescope spatial CoRoT (Convection, Rotation et Transit planétaires), lancé en décembre 2006, est doté d'un photomètre de haute précision permettant à la fois l'étude de la structure interne des étoiles par astérosismologie et la détection de planètes par la méthode des transits. Pour cette thèse, j'ai développé différents outils informatiques permettant la détection, l'analyse détaillée de transits dans les courbes de lumière de CoRoT. J'ai appliqué ces outils aux quelques 12 000 étoiles observées durant chacune des dix premières campagnes d'observation. La collaboration des équipes de détection et de suivi au sol par d'autres méthodes d'observation a permis, à ce jour, la découverte de quinze planètes et deux naines brunes.Il est possible de contraindre les modèles de ces exoplanètes grâce à la connaissance des paramètres (masse, rayon): gazeuses, de glace, telluriques, ou d'autres types mixtes.La recherche de planètes rocheuses en particulier est un objectif motivé tant par la rareté des détections de ces objets jusqu'à présent (liée à leur faibles rayon et masse), que par la grande variété potentielle de leur nature.Ainsi, la découverte de CoRoT-7b, la première exoplanète compatible avec un modèle rocheux et dont le rayon (1,6 rayon terrestre) et la masse (environ 7 masses terrestres) ont pu être mesurés, a permis d'élaborer un modèle physique auquel j'ai contribué.J'ai étudié la possibilité d'observer cette planète très chaude en proche infrarouge avec le JWST, au cours de son orbite, afin d'estimer le contraste de température entre les faces jour et nuit. Ceci doit permettre de confirmer / invalider notre modèle qui suppose l'absence d'une atmosphère suffisamment dense pour redistribuer la chaleur à la surface de CoRoT-7b
The transit photometry makes it possible to detect exoplanets by measuring their radii. Pursuing this goal, the space telescope CoRoT (Convection, Rotation and planetary Transits), launched in December 2006, is equiped with a high-precision photometer allowing both planet detection by transit photometry, and stellar physics studies (asteroseismology).For this PhD thesis, I have developed various computing tools for the detection and detailed analysis of the transits in CoRoT light curves. I have applied these tools to almost 12 000 stars observed during each of the first ten campaigns of observation. The collaboration between the detection and ground based follow-up teams led to the discovery, up to now, of fifteen planets and two brown dwarfs.It is possible to constrain the physical natures of these exoplanets thanks to the knowledge of the masses and radii: they can be gazeous, icy, rocky or with an mixed nature.The search for rocky planets in particular, is a goal motivated by their singular nature, and both by the paucity of detections of these objects (due to their low masses and radii), Thus, the discovery of CoRoT-7b -- the first exoplanet compatible with a rocky model and whith measured radius (1.6 Earth radius) and mass (around 7 Earth masses) -- allowed us to develope a physical model to which I contributed :I studied the possibility of observing this very hot planet in the near infrared range with JWST, during its orbit, to estimate the temperature contrast between the day and the night faces. This should allow to confirm / invalidate our model with atmosphere dense enough to redistribute heat at the surface of CoRoT-7b

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.
This thesis was scanned as part of an electronic thesis pilot project.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 181-187).
After centuries of studying the eight planets in our solar system, recent improvements in technology have given us the unprecedented opportunity to detect planets orbiting stars other than the sun, so-called exoplanets. Recent statistical studies based on 800 confirmed planets and more than 3000 planet candidates suggest that our galaxy is teeming with billions of planets. Many of them are likely to orbit their host stars at a distance where liquid water and potentially life can exist. Spectroscopic observations of exoplanets can provide us with information about the atmospheres and conditions on these distant worlds. This thesis presents a Bayesian retrieval framework to analyze spectroscopic observations of exoplanets to infer the planet's atmospheric compositions, the surface pressures, and the presences of clouds or hazes. I identify what can unambiguously be determined about the atmospheres of exoplanets by applying the retrieval method to sets of synthetic observations. The main finding is that a unique constraint of the atmospheric mixing ratios of all infrared absorbing gases and up to two spectrally inactive gases is possible if the spectral coverage of the observations is sufficient to (1) determine the broadband transit depths in at least one absorption feature for each absorbing gas and (2) measure the slope and strength of the molecular Rayleigh scattering signature. For the newly discovered class of low-density super-Earths, with radii and masses intermediate between Earth and Neptune, I present an observational approach to distinguish whether these planets more closely resemble the giant planets in our solar system or whether they represent a completely new, potentially water vapor-rich type of planet. The approach discussed in this work represents the science case for the largest Hubble Space Telescope program ever awarded for a single exoplanet. The numerical methods and the conceptual understanding of atmospheric spectra presented in this thesis are key for the design of future space telescopes dedicated to the characterization of transiting exoplanets. I present an integrated design evaluation framework for the proposed Exoplanet Characterization Observatory (EChO) that simultaneously models the astrophysical signal and the telescope's payload module. I demonstrate that costly cryogenic cooling to observe the mid-infrared spectrum beyond ~ 11 [mu]m is not required while visible light observations down to - 400 nm are essential for the mission success. The observational study of exoplanet atmospheres is in its infancy and its pace is poised to accelerate as observational techniques are improved and dedicated space missions are designed. The methods developed in this thesis will contribute to constraining the atmospheric properties of a wide variety of planets ranging from blazingly-hot gas giants to temperate Earth-like planets.
by Björn Benneke.
Ph.D.

O principal objetivo do trabalho foi estimar a possibilidade de sobrevivência de micro-organismos extremófilos na superfície de exoplanetas conhecidos, assim como na superfície de seus eventuais satélites naturais. Foi utilizado um modelo que simula a atmosfera terrestre primordial, composta principalmente por nitrogênio, água e dióxido de carbono. E em se tratando de extremófilos, esses cálculos não foram limitados à Zona Habitável dos sistemas planetários, pois esse conceito foi estendido para uma região mais ampla, a Zona Extremófila, onde a vida pode existir. Extremófilos são micro-organismos terrestres que vivem sob condições extremas de temperatura, nível de radiação, umidade, pressão, salinidade, pH, etc. . Eles são candidatos naturais para habitarem meios ditos extraterrestres onde tais condições são eventualmente encontradas. Alguns exemplos desses ambientes em nosso sistema solar são: Marte, Titã (satélite de Saturno) e Europa (satélite de Júpiter). Há algumas centenas de planetas orbitando outras estrelas (exoplanetas) e a maioria deles são gigantes gasosos, em particular Hot Jupiters. A temperatura superficial de um planeta depende fortemente de seu albedo, de sua distância orbital, de condições geodinâmicas intrínsecas, além do tipo espectral de sua estrela hospedeira. A estimativa dessa temperatura foi obtida considerando o ciclo silicato-carbono e um balanço de energia global, que contribuiram para se obter estimativas da pressão parcial atmosférica devido ao dióxido de carbono e da temperatura média, na superfície dos planetas e/ou de seus satélites hipotéticos. Os eventuais satélites naturais de planetas gigantes podem abrigar vida e essa possibilidade foi testada através da análise das condições de estabilidade orbital desses corpos celestes. Os resultados deste trabalho deverão fornecer subsídios para a hipótese da panspermia.
The main objective of this study is to estimate the chance of survival of microorganisms (extremophiles) on the surface of known exoplanets, as well as on the surface of its potential natural satellites. We used a model that simulates the primordial atmosphere composed by, primarily, nitrogen, water and carbon dioxide. And when it comes to extremophiles, these calculations were not limited to the Habitable Zone of planetary systems, since this concept was extended to a wider region, the Extremophile Zone, where life can exist. Extremophiles are terrestrial microorganisms living under extreme conditions of temperature, light level, humidity, pressure, salinity, pH, etc ... They are natural candidates for living in habitats considered extraterrestrials where such conditions are encountered eventually. Examples of such environments in our solar system are: Mars, Titan (moon of Saturn) and Europe (satellite of Jupiter). There are hundreds of planets orbiting other stars (exoplanets) and most of them are gas giants, particularly Hot Jupiters. The surface temperature of a planet/moon depends heavily on its albedo, its orbital distance, of geodynamic conditions intrinsic, in addition to the spectral type of their host star. The estimate of this temperature was obtained considering the carbon-silicate cycle and a global energy balance, which contributed to obtain estimates of the partial pressure due to atmospheric CO2 and the average temperature on the surface of planets and/or their hypothetical satellites. Natural satellites of giant planets may harbor life, and this possibility was tested by analyzing the conditions of orbital stability of these heavenly bodies. The results of this study should provide support for the hypothesis of panspermia.

This report provides a description of the development and implementation of an Exoplanet visualization within the interactive astro-visualization software OpenSpace. Orbital Data from The Exoplanet Orbit Database were used to render the planetary systems around stars known to have exoplanets in orbit. The uncertainties of the data in the database were incorporated into the design of the visualization. A feature that visualizes the discovery method of exoplanets was also implemented.

In my PhD, I advanced the scientific exploration of the Next Generation Transit Survey (NGTS), a ground-based wide-field survey operating at ESO’s Paranal Observatory in Chile since 2016. My original contribution to knowledge is the development of novel methods to 1) estimate NGTS’ yield of planets and false positives; 2) disentangle planets from false positives; and 3) accurately characterise planets. If an exoplanet passes (transits) in front of its host star, we can measure a periodic decrease in brightness. The study of transiting exoplanets gives insight into their size, formation, bulk composition and atmospheric properties. Transit surveys are limited by their ability to identify false positives, which can mimic planets and out-number them by a hundredfold. First, I designed a novel yield simulator to optimise NGTS’ observing strategy and identification of false positives (published in Günther et al., 2017a). This showed that NGTS’ prime targets, Neptune- and Earth-sized signals, are frequently mimicked by blended eclipsing binaries, allowing me to quantify and prepare strategies for candidate vetting and follow-up. Second, I developed a centroiding algorithm for NGTS, achieving a precision of 0.25 milli-pixel in a CCD image (published in Günther et al., 2017b). With this, one can measure a shift of light during an eclipse, readily identifying unresolved blended objects. Third, I innovated a joint Bayesian fitting framework for photometry, centroids, and radial velocity cross-correlation function profiles. This allows to disentangle which object (target or blend) is causing the signal and to characterise the system. My method has already unmasked numerous false positives. Most importantly, I confirmed that a signal which was almost erroneously rejected, is in fact an exoplanet (published in Günther et al., 2018). The presented achievements minimise the contamination with blended false positives in NGTS candidates by 80%, and show a new approach for unmasking hidden exoplanets. This research enhanced the success of NGTS, and can provide guidance for future missions.

This work characterises PIRATE’s primary camera, the SBIG STX-16803, as well as assessing the usefulness and impact of a small-aperture semi-autonomous facility in Mallorca for exoplanet studies and studies of transient sources. Additionally, a method for exploring the Roche lobe of an exoplanet and the effects this has on the shape and density of the planet is also described. PIRATE is a small aperture photometric facility that can be operated remotely or autonomously, is constructed from commercially available hardware and utilised by The Open University for research, education and outreach. The camera gain measurements are within the manufacturer specifications while the read noise deviates quite significantly. The camera shutter is also verified to evenly illuminate the CCD which may be suffering from a form of residual image. Regarding exoplanets, PIRATE has helped to identify 108 false positives as well as 24 real and plausible planets. Combined, this is 67% of PIRATE’s total exoplanet candidate observations. Several of these targets are explored in further detail. Still on the subject of exoplanets, Roche calculations are applied to 207 known exoplanets and highlight that WASP-12b, WASP-19b and WASP-103b are likely to have strong distortions from a spherical shape. Look-up charts were also generated for mass ratios of 10^-6 through to 10^-1. These look-up charts are intended to provide a quick reference volume correction to exoplanets (or any other system of similar mass ratios). As part of the Gaia transient preparatory and to demonstrate the capabilities of PIRATE, SN 2014J is provided as an example. A peak B apparent magnitude, Bmax of 11.80 +/- 0.14 mag is observed at a tmax of 56690.79 +/- 0.01 MJD and provides Dm15 = 0.98 +/- 0.20 mag. A peak E(B-V) extinction of 1.24 +/- 0.16 mag (E(B-V)host = 1.19 +/- 0.16 mag) is determined.

The study of extrasolar planets (in short, "exoplanets") is one of the most young and rapidly-evolving fields of astronomical research. The present thesis is primarily about the development of new observational and reduction/analysis techniques to 1) characterize known transiting extrasolar planets by means of high-precision, ground-based differential photometry 2) to exploit the same data to search for additional bodies in known planetary systems, by employing the so-called Transit Time Variation (TTV) analysis. For both aims, I developed independent and customized software pipelines targeted at minimizing or correcting every significant source of uncorrelated ("red") noise. Most of my thesis is focused on the design and implementation of the TASTE project (once known as "The Asiago Search for Timing time variations of Exoplanets"), a long-term and multi-site photometric campaign to follow up a selected sample of transiting exoplanets at small/medium-sized facilities. The contents of each chapter in summarized in what follows: 1) Introduction. In this chapter I will briefly discuss the present status of exoplanetary research, including an overview of the main techniques employed so far to detect and characterize exoplanets. Then I will discuss why and how we are looking for smaller and lighter planets around bright stars, and what techniques have been developed to work out the resulting instrumental issues. In particular, I will describe what the TTV technique is, its theoretical basis and how it can be applied to real measurements. I will also review the first results obtained with this method, both from ground-based facilities and from CoRoT and Kepler space missions. 2) The implementation of TASTE. In this chapter I will describe the design and implementation of the TASTE project, as originally conceived to be operated at one single facility (the 1.82m telescope at the Asiago Observatory). I will discuss the technical requirements, the criteria adopted for the selection of the target sample, the observing strategy, and the first version of the STARSKY pipeline, optimized to carry out differential photometry on defocused images. I will present the first two light curves of the "hot Jupiters" HAT-P-3b and HAT-P-14b gathered by TASTE, and demonstrate that they achieve the accuracy required to detect Earth-mass perturbers through TTVs, if locked on low-order orbital resonances such as 3:2 or 2:1. This chapter is based on: V. Nascimbeni, G. Piotto, L. R. Bedin, M.Damasso (2011): TASTE: The Asiago Search for Transit timing variations of Exoplanets. I. Overview and improved parameters for HAT-P-3b and HAT-P-14b, A&A, 527, A85. 3) A new observational study of HAT-P-13b. In this chapter I will present the first observational TTV study published by the TASTE collaboration. This work was prompted by a paper of Pal et al. (2011), who claimed the detection of a sizeable TTV in the transits of HAT-P-13b (an interesting hot Jupiter hosted by a multiplanetary system). I will show that TASTE data are in agreement with the Pal et al. (2011) measurements, supporting --along with other archival data-- the possible presence of a periodic TTV signal. I will point out how subsequent works (Southworth et al. 2012, Fulton et al. 2012) demonstrated that most past timing measurements were published with underestimated errors caused by neglected red noise, thus disproving the previously claimed TTV for this system. This chapter is based on: V. Nascimbeni, G. Piotto, L. R. Bedin, M. Damasso, L. Malavolta, L. Borsato (2011): TASTE II. A new observational study of transit time variations in HAT-P-13b, A&A, 532, A24. 4) A homogeneous study of WASP-3b. In this chapter I will present the first TASTE work based on observations made at IAC facilities, namely a new study of the hot Jupiter WASP-3b from six high-precision light curves secured at the IAC-80 telescope. I will describe the thorough (re-)analysis carried out on both archival and our data, employing homogeneous techniques and software tools, with the goal of deriving auto-consistent planetary parameters and timing measurements. I will show that our ensemble data set is not in agreement with the periodic TTV previously claimed by Maciejewski et al. (2010). Instead, I will demonstrate that the measured TTV scatter is indeed statistically significant, though it does not show any significant periodicity. Hence I will discuss the possible causes for that behavior, and present an updated ephemeris and improved orbital/physical parameters for this target. This chapter is based on: V. Nascimbeni, A. Cunial, S. Murabito, P. V. Sada, A. Aparicio, G. Piotto, L. R. Bedin, A. P. Milone, A. Rosenberg, L. Borsato, M. Damasso, V. Granata, and L. Malavolta (2012): TASTE III. A homogeneous study of transit time variations in WASP-3b, A&A, submitted. 5) Improved parameters for WASP-1b and HAT-P-20b. In this chapter I will analyze four high-precision light curves caught serendipitously at the Asiago 1.82m telescope (one of WASP-1b, three of HAT-P-20b). By also re-analyzing the most accurate archival data available, I will derive improved parameters and ephemeris for both targets, which do not show any significant TTV. I will discuss what upper limits can be set from this null detection to the mass of hypotetical perturbing planets. This chapter is based on: V. Granata, V. Nascimbeni, G. Piotto, L. R. Bedin, L. Borsato, M. Damasso, L. Malavolta (2012): TASTE IV. Refined ephemeris and parameters for WASP-1b and HAT-P-20b, A&A, in preparation. 6) A search for planets in NGC 6397. In this chapter I will describe a search for transiting planets and variable stars carried out in an outer field of the globular cluster NGC 6397 from space-based HST observations. The main sample is a set of ~2200 cluster-member M dwarfs belonging to the same stellar popolation. I will describe the algorithms I developed to correct systematic errors in a data set composed by 252 ultra-deep archival images from the ACS camera. As no transits were detected, I will discuss the significance of this null result. I will report twelve unpublished variables of various types, all of them discovered among field stars. This chapter is based on: V. Nascimbeni, L. R. Bedin, G. Piotto, F. De Marchi, R. M. Rich (2012): An HST search for planets in the lower Main Sequence of the globular cluster NGC 6397, A&A, 541, A144. 7) Field selection for PLATO} In the final chapter I will summarize my involvement in PLATO. Plato is a proposed ESA mission that will search primarily for low-mass, habitable planets around bright stars, covering up to the ~40% of the sky at the end of the mission. Suitable targets (dwarfs and subgiants later than spectral type F5, down to V~13) have to be selected in advance. An unprecedented all-sky stellar classification is then needed. Within the Working Package (WP 131210: "Analysis of photometric and astrometric catalogues") I evaluated the feasibility and reliability of stellar classification techniques based upon the existing and forthcoming photometric/astrometric catalogs.
Lo studio dei pianeti extrasolari (o "esopianeti") è una branca della ricerca astronomica molto giovane e in rapidissima evoluzione. Il lavoro svolto nella presente tesi riguarda principalmente lo sviluppo di nuove tecniche di osservazione e di riduzione e analisi dati al fine di 1) caratterizzare pianeti extrasolari transitanti già noti attraverso fotometria differenziale di alta precisione, condotta da terra; e 2) fare uso degli stessi dati per cercare nuovi corpi in sistemi planetari già noti, sfruttando una tecnica di analisi nota come TTV (Transit Time Variation: variazione dei tempi di transito). Per entrambi gli scopi, ho sviluppato strumenti software indipendenti e mirati al fine di minimizzare o correggere ogni sorgente rilevante di errori sistematici (noto anche come "correlated noise" o "red noise"). Gran parte della mia tesi è focalizzata sulla progettazione e implementazione del progetto TASTE, una campagna osservativa multisito e a lungo termine per monitorare un campione selezionato di esopianeti con telescopi terrestri di classe piccola e media. Il contenuto di ciascun capitolo è riassunto in seguito. 1) Introduzione. In questo capitolo tratterò in breve la situazione attuale della ricerca sugli esopianeti, comprendente anche una panoramica sulle principali tecniche finora impiegate per rivelare e caratterizzare pianeti extrasolari. Quindi passerò a discutere perché e come la comunità scientifica si sta orientando verso la ricerca di pianeti sempre più piccoli e leggeri attorno a stelle brillanti, e illustrerò le tecniche sviluppate per aggirare i limiti attualmente imposti dagli strumenti. In particolare, descriverò in cosa consiste la tecnica TTV, quali sono i principi teorici sui quali si fonda e come questi possano essere applicati a misure reali. Passerò infine in rassegna i primi risultati ottenuti applicando questo metodo, sia da strumentazioni terrestri che dalle missioni spaziali Kepler e CoRoT. 2) Implementazione del progetto TASTE. In questo capitolo descriverò la progettazione e l'implementazione di TASTE nella configurazione originaria: ovvero, come un progetto concepito per un singolo telescopio (il riflettore Copernico da 1.82m presso l'Osservatorio Astrofisico di Asiago). Discuterò i requisiti tecnici imposti, i criteri adottati per la selezione del campione di oggetti, la strategia osservativa e la prima versione della pipeline software STARSKY, ottimizzata per eseguire fotometria differenziale di apertura su immagini appositamente sfuocate. Presenterò le prime curve di luce pubblicate da TASTE, dei pianeti cosiddetti "hot Jupiters" HAT-P-3b e HAT-P-14b, e dimostrerò che esse raggiungono l'accuratezza fotometrica necessaria per rilevare con la tecnica TTV pianeti perturbatori di massa terrestre, nel caso questi ultimi siano bloccati in una risonanza orbitale di basso ordine, come 3:2 o 2:1. Questo capitolo è basato sull'articolo: V. Nascimbeni, G. Piotto, L. R. Bedin, M. Damasso (2011): TASTE: The Asiago Search for Transit timing variations of Exoplanets. I. Overview and improved parameters for HAT-P-3b and HAT-P-14b, A&A, 527, A85. 3) Un nuovo studio osservativo di HAT-P-13b. In questo capitolo presenterò il primo studio TTV osservativo pubblicato dalla collaborazione TASTE. Questo lavoro è stato stimolato da un articolo di Pal et al. (2011) che rivendicava la scoperta di un considerevole segnale TTV nei transiti del pianeta HAT-P-13b (un caso interessante di "hot Jupiter" ospitato da un sistema planetario multiplo). Mostrerò che i dati raccolti da TASTE sono in accordo con le misure di Pal et al. (2011), il che conforta --assieme ad altri dati di archivio-- la possibile presenza di un segnale TTV periodico. Infine metterò in evidenza che lavori più recenti (Southworth et al. 2012, Fulton et al. 2012) hanno tentato di dimostrare che molte misure condotte in passato sono state pubblicate con errori di gran lunga sottostimati, a causa della presenza di red noise trascurato durante la fase di analisi di dati. Per questo motivo, oggi si ritiene probabile che la rivendicazione di Pal et al. (2011) sia spuria. Questo capitolo è basato sull'articolo: V. Nascimbeni, G. Piotto, L. R. Bedin, M. Damasso, L. Malavolta, L. Borsato (2011) TASTE II. A new observational study of transit time variations in HAT-P-13b, A&A, 532, A24. 4) Un'analisi omogenea del sistema WASP-3. In questo capitolo presenterò il primo lavoro del progetto TASTE basato su osservazioni condotte presso l'Observatorio del Teide dell'Instituto de Astrofisica de Canarias (IAC): sei curve di luce ad alta precisione ottenute con il telescopio IAC-80. Descriverò l'analisi approfondita che è stata svolta sia su dati di archivio che sulle nostre misure, facendo uso di tecniche e software di riduzione/analisi omogenei. Lo scopo è di derivare parametri del pianeta e misure di tempo di transito in modo completamente autoconsistente. Illustrerò come l'insieme dei dati disponibili non sia in accordo con il presunto segnale TTV periodico rivendicato da Maciejewski et al. (2010). Al contrario, dimostrerò che la dispersione delle misure TTV è statisticamente significativa, sebbene priva di qualsiasi tipo di periodicità rivelabile. Passerò quindi a discutere le possibili cause di questo comportamento, presentando un'effemeride aggiornata per WASP-3b e ricavando per lo stesso parametri fisici e orbitali aggiornati. Questo capitolo è basato sull'articolo: V. Nascimbeni, A. Cunial, S. Murabito, P. V. Sada, A. Aparicio, G. Piotto, L. R. Bedin, A. P. Milone, A. Rosenberg, L. Borsato, M. Damasso, V. Granata, and L. Malavolta (2012) TASTE III. A homogeneous study of transit time variations in WASP-3b, A&A, submitted. 5) Parametri fisici e orbitali di WASP-1b e HAT-P-20b. In questo capitolo analizzerò quattro curve di luce di alta precisione ottenute serendipicamente con il telescopio da 1.82m di Asiago (un transito di WASP-1b e tre transiti completi di HAT-P-20b). Rianalizzando anche i più accurati dati di archivio attualmente disponibili, derivererò un'effemeride e dei parametri fisici e orbitali più precisi per entrambi i pianeti. Nessuno dei due mostra un segnale TTV significativo. Discuterò infine quali limiti superiori possono essere stimati riguardo alla massa di un ipotetico pianeta perturbatore in base a questa misura nulla. Questo capitolo è basato sull'articolo: V. Granata, V. Nascimbeni, G. Piotto, L. R. Bedin, L. Borsato, M. Damasso, L. Malavolta (2012) TASTE IV. Refined ephemeris and parameters for WASP-1b and HAT-P-20b, A&A, in preparation. 6) Una ricerca di pianeti in NGC 6397 In questo capitolo descriverò una ricerca di pianeti transitanti e stelle variabili condotta in un campo stellare periferico dell'ammasso globulare NGC 6397, sfruttando osservazioni di archivio del telescopio spaziale Hubble. Il campione principale è costituito da un insieme di ~2200 nane rosse appartenenti all'ammasso. Descriverò gli algoritmi che ho sviluppato per correggere gli errori fotometrici sistematici presenti in un insieme di 252 immagini ultraprofonde riprese con la camera ACS nel 2006. Poiché non sono stati rivelati transiti, discuterò la significatività di questo risultato nullo. Infine, descriverò e caratterizzerò dodici stelle variabili di diverse tipologie scoperte per la prima volta. Tutte queste variabili sono sorgenti di campo, non appartenenti all'ammasso. Questo capitolo è basato sull'articolo: V. Nascimbeni, L. R. Bedin, G. Piotto, F. De Marchi, R. M. Rich (2012) An HST search for planets in the lower Main Sequence of the globular cluster NGC 6397, A&A, 541, A144. 7) Selezione del campo di vista di PLATO Nell'ultimo capitolo passerò in rassegna il lavoro che mi ha visto coinvolto nello studio preparatorio per PLATO. PLATO è una missione spaziale proposta all'ESA che cercherà principalmente pianeti "abitabili" di piccola massa attorno a stelle brillanti, coprendo alla fine della missione un angolo sferico pari al ~40% dell'intero cielo. I target adatti comprendono stelle nane e subgiganti di tipo spettrale F5V e più freddi, più brillanti della magnitudine V~13. Tali target devono essere selezionati prima dell'inizio della missione vera e propria, pertanto è necessaria una classificazione stellare su tutto il cielo, e molto più profonda di quelle attualmente disponibili. All'interno del gruppo di lavoro WP 131210 ("Analysis of photometric and astrometric catalogues") ho investigato la fattibilità e l'affidabilità delle tecniche di classificazione stellare basate sui cataloghi fotometrici e astrometrici, sia quelli disponibili che quelli di prossima realizzazione.

L'utilisation des microlentilles gravitationnelles dans la recherche d'exoplanètes a débuté en 1995. Les premiers résultats furent rapides, puisque la première exoplanète fut détectée en 2003 par les collaborations MOA et OGLE. Aujourd'hui, plus de vingt exoplanètes ont été publiées et ce nombre va considérablement augmenter dans les prochaines années avec le lancement des télescopes de surveillance KMTNet et les observatoires spatiaux EUCLID et WFIRST. Lorsqu'une étoile "proche", la microlentille, croise la ligne de visée entre la Terre et une étoile plus distante, la source, le flux de cette dernière est alors amplifié. Si par chance, une planète orbite autour de cette lentille, elle va également produire une amplification de faible amplitude. La courbe de lumière de l'évènement présente alors une signature typique : la déviation planétaire. Dans ce manuscript, nous présentons tous les outils théoriques et observationnels nécessaires à la détection d'exoplanète par la méthode des microlentilles gravitationnelles. Nous présentons ensuite l'étude de deux cas spécifiques : MOA- 2010-BLG-411Lb, une binaire composée d'une naine brune autour d'une naine M, et MOA-2010-BLG-477Lb, un super-Jupiter orbitant une étoile M. Une uniformisation des résultats sur les planètes détectées par effet de mircolentille gravitationnelle est également présentée. Deux problèmes majeurs compliquent la détection de planètes par la méthode des microlentielles gravitationnelles. Premièrement, le phénomène de microlentille gravitationnelle est peu probable pour une étoile donnée (une chance sur un million). Il faut donc observer des champs très riche en étoiles, tel que le Bulbe Galactique. Chaque nuit, les collaborations OGLE et MOA observe le Bulbe Galactique afin de repérer les évènements de microlentilles. Le second problème est que les déviations planétaires sont très courtes, d'une durée d'une heure à quelques jours pour les planètes les plus massives. Il faut donc observer les évènements de microlentilles en continu. C'est pour cela qu'une batterie de télescopes est répartie sur tout l'Hémisphère Sud. Le nombre d'évènements détectés chaque saison a considérablement augmenté durant les dernières années, obligeant les télescopes de suivi à faire des choix quand aux cible à observer. Nous avons décidé de développer un nouveau logiciel automatique permettant de faire ce choix à notre place. Il a été testé sur quatre années d'observations et l'analyse statistique des résultats est présentée. Nous espérons utiliser ces nouveaux résultats pour mieux contraindre un modèle de notre Galaxie
The search of exoplanets using gravitational microlensing started in 1995. First results come quickly and the first exoplanet has been detected on 2003 by the OGLE and the MOA collaborations. Nowadays, more than twenty exoplanets are published and the number of detections should rise a lot in the coming years with the launch of KMTNet survey and EUCLID and WFIRST space-based observatories. When a "close" star, the lens, cross the line of sight between the Earth and a more distant star, the source, the luminosity of this source is magnified. By chance, if a planet orbits this lens star, it produces a second magnification of lower amplitude. The lightcurve of the event then shows a typical signature : a planetary deviation. In this manuscript, we present the theoritical and observational tools needed to detect planets with gravitational microlensing. We present two studies on two special events : MOA-2009-BLG-411L, a lens formed by a brown dwarf around an M-dwarf, and MOA-2010-BLG-477Lb, a super-Jupiter orbiting an M star. We finally present a study on planets already published in order to standardize theses results. Two major problems make this research difficult. First, the occurence of a microlensing event for a single star is very low (one in a million). We then need to observe very dense fields, such as the Galactic Bulge. Each night, OGLE and MOA surveys analyze the Galactic Bulge to detect events. The second problem is the planetary deviation is very short, one hour to few days for most massive planets. This is why we have to continously observe events and use telescopes all around the Southern Hemisphere. The rapid increase of detection during the last years forces the follow-up telescopes to choose which targets they need to observe. We so decided to develop a new software to make automatically this choice. At the end of this manuscript, we present a statistical study of microlensing parameters from four observational seasons. We expect these results will help to constrain theoritical model of the Milky Way in the future

The combined observations of a planet’s transits and the radial velocity variations of its host star allow the determination of the planet’s orbital parameters, and most inter- estingly of its radius and mass, and hence its mean density. Observed densities provide important constraints to planet structure and evolution models. The uncertainties on the parameters of large exoplanets mainly arise from those on stellar masses and radii. For small exoplanets, the treatment of stellar variability limits the accuracy on the de- rived parameters. The goal of this PhD thesis was to reduce these sources of uncertainty by developing new techniques for stellar variability filtering and for the determination of stellar temperatures, and by robustly fitting the transits taking into account external constraints on the planet’s host star. To this end, I developed the Iterative Reconstruction Filter (IRF), a new post-detection stellar variability filter. By exploiting the prior knowledge of the planet’s orbital period, it simultaneously estimates the transit signal and the stellar variability signal, using a com- bination of moving average and median filters. The IRF was tested on simulated CoRoT light curves, where it significantly improved the estimate of the transit signal, particu- lary in the case of light curves with strong stellar variability. It was then applied to the light curves of the first seven planets discovered by CoRoT, a space mission designed to search for planetary transits, to obtain refined estimates of their parameters. As the IRF preserves all signal at the planet’s orbital period, t can also be used to search for secondary eclipses and orbital phase variations for the most promising cases. This en- abled the detection of the secondary eclipses of CoRoT-1b and CoRoT-2b in the white (300–1000 nm) CoRoT bandpass, as well as a marginal detection of CoRoT-1b’s orbital phase variations. The wide optical bandpass of CoRoT limits the distinction between thermal emission and reflected light contributions to the secondary eclipse. I developed a method to derive precise stellar relative temperatures using equiv- alent width ratios and applied it to the host stars of the first eight CoRoT planets. For stars with temperature within the calibrated range, the derived temperatures are con- sistent with the literature, but have smaller formal uncertainties. I then used a Markov Chain Monte Carlo technique to explore the correlations between planet parameters derived from transits, and the impact of external constraints (e.g. the spectroscopically derived stellar temperature, which is linked to the stellar density). Globally, this PhD thesis highlights, and in part addresses, the complexity of perform- ing detailed characterisation of transit light curves. Many low amplitude effects must be taken into account: residual stellar activity and systematics, stellar limb darkening, and the interplay of all available constraints on transit fitting. Several promising areas for further improvements and applications were identified. Current and future high precision photometry missions will discover increasing numbers of small planets around relatively active stars, and the IRF is expected to be useful in characterising them.

This study presents the development of an observing program to pursue the idea of looking for transiting exoplanets in eclipsing binary stars. The various kinds of orbits a planet might have in a binary system are explored. From this it is shown how to anticipate the possible orbits a planet might have in a given star system. The potential detectability of a planet in a binary system is also analyzed. Together these guidelines enable observers to rank targets by the likelihood that a detectable planet might exist in the system. The results of observations by a team at Ball State University of five binary star systems chosen with these guidelines are presented.
Department of Physics and Astronomy

This thesis primarily considers evolved exoplanetary systems through the use of asteroseismology as a tool to investigate the fundamental properties of the host stars, and the inferred planetary parameters. Of particular interest are the masses of evolved stars, and investigating how the available observables may bias the recovered mass estimates. Accurate and precise stellar masses are of critical importance. Whilst most of this work considers ensemble analysis, where relevant individual systems are considered, including a binary star system with an M dwarf and an asteroseismic red giant primary star. Another system of note is a transiting gas giant orbiting a red giant host, that will be consumed by the expansion of the host star. The metallicity distributions of evolved exoplanet hosts, and a suitable ensemble of field stars are also investigated using spectroscopy. This is to determine if evolved giant planet exoplanet hosts display the same metallicity excess seen in main sequence giant planet hosts. We fail to find a statistically significant excess in metallicity. Finally the noise properties of evolved stars are considered, including predicting the noise properties from stellar parameters, and how the elevated noise levels in evolved stars impact the detectable of planets around them.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.
Includes bibliographical references (leaves 101-102).
This thesis presents time-series photometry of transits of 11 different extrasolar planets. Observations were conducted with the Fred L. Whipple Observatory 1.2m telescope and the Wise Observatory im telescope, in standard optical bandpasses. The number of transits observed for each planet ranges between one and 20 transits, and differential aperture photometry is performed for each transit observation. For the system TrES-2, this thesis examines 14 different different transit observations. Because of this large quantity of data, the parameters Rp/R., b, a/R., and i are also fitted for with precision using the Markov Chain Monte Carlo technique, and the resultant parameter values are presented. Transit-timing analysis is performed on all systems: CoRoT-2, GJ436, HAT-P-1, HD17156, HD189733, TrES-1, TrES-2, WASP-2, WASP-3, XO-1, XO-2, and XO-3. Transit timing is important both for constraining the orbital period and to search for variations in the transit-to-transit interval that could indicate the presence of an unseen companion planet. The transit center times for nearly all observations are found, and the planetary periods for all systems are calculated. In many cases these periods are determined with much greater precision than previously known. It is found that systems XO-2 and HAT-P-1 are consistent with a constant period, but our data are not conclusive with regards to the other systems.
by Katherine Rebecca de Kleer.
S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 57-58).
Transits of exoplanets were observed from June 2009 through January 2010. Six transit light curves are presented in this paper for three planets: WASP-10b, WASP- 11/HAT-P-10b, and TrES-3. Measurements of the planetary radii, semi-major axis, transit duration, and period confirmed literature values to within two sigma. Transit timing variations were not observed in these systems, but calculations show that it would be possible to measure transit timing variations induced by large exomoons (greater than about 6 Earth masses) in the WASP-11/HAT-P-10b system. Challenges of exoplanet observation from small telescopes are discussed. It was determined that overall, transit measurements of many exoplanets using small telescopes can be successful and scientifically useful.
by Caroline V. Morley.
S.B.

The detection of Earth-like exoplanets and the characterization of their atmospheres is a challenge one needs to solve to assess their habitability and the presence of life in the universe. If this challenge is still unresolved today, even in the era of giant telescopes, it is mainly because of the very high contrast between these exoplanets and their host star and also their proximity. To overcome both of these constraints, a new method combining high-dispersion spectroscopy and nulling interferometry has been imagined. The idea is to use the nulling interferometry to attenuate the star light emission and detect the inner rocky planets with a high angular resolution. The high-dispersion spectroscopy is increasing the exoplanet detectability significantly which enables to relax the star attenuation requirement for an Earth-like observation. Our simulation made for an exoplanet similar to the Earth orbiting Proxima Centauri is giving a condition for the star attenuation ∼10−4 to detect it. Given this condition, we are able to evaluate the unability of a photonic device at our disposal to achieve such performance without dealing with its limitations. If a future project manages to overcome these limitations, this device could be part of a precursor instrument at IPAG to demonstrate experimentally the performance of high-dispersion nulling interferometry.
Upptäckten av jordliknande exoplaneter och karakteriseringen av deras atmosfärer är en utmaning man behöver lösa för att bedöma deras beboelighet och närvaron av liv i universum. Om denna utmaning fortfarande inte är löst idag, även i jätteteleskopens tid, beror det främst på den mycket höga kontrasten mellan dessa exoplaneter och deras värdstjärna och också deras närhet. För att övervinna båda dessa begränsningar har en ny metod som kombinerar högdispersionsspektroskopi och nullingsinterferometri föreställts. Idéen är att använda nullingsinterferometrin för att minska stjärnljusemissionen och upptäcka de inre steniga planeterna med hög vinkelupplösning. Spektroskopin med hög dispersion ökar exoplanetens detekterbarhet betydligt vilket gör det möjligt att minska stjärndämpningsbehovet för en jordliknande observation. Vår simulering för en exoplanet som liknar jorden som kretsar omkring Proxima Centauri ger ett tillstånd för stjärndämpningen att ∼10−4 för att upptäcka den. Med tanke på detta villkor kan vi utvärdera oförmågan hos en fotonisk enhet till vårt förfogande för att uppnå sådan prestanda utan att hantera dess begränsningar. Om ett framtida projekt lyckas övervinna dessa begränsningar kan den här enheten vara en del av ett föregångarinstrument på IPAG för att experimentellt visa prestanda för högdispersionsnullningsinterferometri.

This thesis sets out to analyse and define an instrument capable of advancing the field of exoplanet research. This exciting and nascent field of astrophysics is moving beyond simple population counts and into more detailed characterisation of exoplanet parameters. To this end high resolution and high contrast missions are required to achieve this. In this thesis three designs were investigated, two pupil masked telescopes and an interferometric system. The First masked design was an axially symmetric system using a petal mask. This design was intended to reduce the diffraction wings resulting from a circular aperture by apodising the pupil. After analysis in software it was found to be insufficient in reducing the airy rings to an acceptable level by a factor of $10^5$ and a new design was sought. Secondly a non axially symmetric mask was tried based on the spergel mask design. This displaced the light from an on axis source away from two detection zones allowing a faint off axis companion to be registered at much higher contrast. Again however the resulting contrast was insufficient to meet science goals. The third design used was an interferometer based on the Intensity Interferometer model of Hanbury Brown and Twiss. The resolution, $<0.5 mas$, and time taken per observation, $< 3600s$ for a signal to noise of 5, of a moderately sized system was found to be within reach. An attempt was made to verify this on in the laboratory. A space based mission profile that outlines this system is included.

This thesis is focused on the photometric analysis of stellar light curves (LCs), to search for variable stars and transiting extrasolar planets. In particular, this study is carried out on crowded fields which include open clusters (OCs). The context of my work is the photometric preparatory survey “The Asiago Pathfinder for HARPS-N” (APHN; PI: Bedin) aimed at characterising OCs (i.e. M44, NGC752, M35, NGC2158 and M67) to be observed with the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N), mounted at the Telescopio Nazionale Galileo (TNG). The APHN survey was also recently extended to an additional sample of OCs which were chosen as targets for the Kepler extended mission K2 (Howell et al. 2014), in view of creating astrophotometric master input catalogues for high-precision photometry of Kepler and K2 data, following the method developed by (Libralato et al. 2015a). We also analysed data coming from other ground-based facilities, such as the SuperWASP or the STELLA1 Telescope. Searches for transiting exoplanets within OCs, while challenging (van Saders & Gaudi 2011), are particularly useful to constrain the properties of both the host star and planet, and to unveil the planetary formation and evolution mechanisms (Janes 1996; Fischer & Valenti 2005). The first part of the thesis reviews the different photometric techniques so far developed and present in the literature to search for exoplanets and, in general, for stellar variability studies (chapter 1). A short review of the principal ground and space-based projects is also given at the end of this chapter. Chapter 2 describes the origin of systematics errors (“red noise”) and gives a description of the methods developed to correct the LCs before the search for variability. A description of the different type of stellar variability and of the algorithms used to search for periodical signals is given in chapter 3. My original analysis of the OCs data is described in the last four chapters, starting from M44 in chapter 4. There, after a description of the observational setup, I discuss the detrending algorithms, the procedure to detect periodic signal, and my results in terms of newly discovered variables, including a study of the gyrochronological period versus colour relation. The following chapters are organised in a similar way, but covering NGC752 (chapter 5), M35 & NGC2158 (chapter 6) and M67 (chapter 7), respectively.
Questa tesi è incentrata sull’analisi fotometrica delle curve di luce stellari (LCs), per ricercare stelle variabili e pianeti extrasolari in transito. In particolare, questo studio viene condotto su campi affollati che includono ammassi aperti. Il contesto del mio lavoro è la mappatura fotometrica preparatoria “The Asiago Pathfinder for HARPS-N” (APHN; PI: Bedin), finalizzata alla caratterizzazione degli ammassi aperti (ad esempio M44, NGC752, M35, NGC2158 and M67), al fine di essere impiegata allo spettrografo HARPS-N (acronimo per High Accuracy Radial velocity Planet Searcher for the Northern hemisphere) installato al Telescopio Nazionale Galileo (TNG). Recentemente, la mappatura APHN è stata estesa ad un campionamento addizionale di ammassi aperti che sono stati scelti quali obiettivi per la missione K2, prolungamento della missione Kepler (Howell et al. 2014), allo scopo di creare un catalogo astro-fotometrico di base delle componenti che verranno analizzate con i set di dati delle missioni Kepler e K2 (Libralato et al. 2015a). Altre strumentazioni sono state coinvolte, come ad esempio quelle del progetto SuperWASP oppure quelle del telescopio STELLA1, i cui dati sono stati analizzati in questa tesi. Le ricerche di esopianeti in transito all’interno di ammassi aperti, benchè ardue (van Saders & Gaudi 2011), sono particolarmente utili per limitare le proprietà sia della stella ospitante, sia del pianeta e di svelare il meccanismo di formazione ed evoluzione planetaria (Janes 1996; Fischer & Valenti 2005). La prima parte della tesi è una recensione delle differenti tecniche fotometriche adottate dalla comunità scientifica nella ricerca di esopianeti e, più in generale, della variabilità stellare (capitolo 1), focalizzandosi sulle mappature fotometriche degli ammassi aperti. Una breve recensione sui principali progetti da terra e da spazio viene data alla fine di questo capitolo. Il capitolo 2 analizza le cause degli errori sistematici (“red noise”) e descrive i metodi sviluppati per correggere le curve di luce prima della ricerca di variabilità. Una descrizione delle differenti tipologie di variabilità stellare e degli algoritmi usati per la ricerca di segnali periodici viene data nel capitolo 3. La mia analisi degli ammassi aperti sopra citati è descritta negli ultimi quattro capitoli, partendo da M44 nel capitolo 4. Qui, dopo una descrizione delle attrezzature per le osservazioni, tratto degli algoritmi per la correzione da errori sistematici, della procedura per individuare segnali periodici e dei miei risultati in termini di variabili appena scoperte, includendo uno studio della relazione girocronologica fra la periodicità e il colore della stella. I capitoli seguenti sono organizzati in maniera simile, ma trattano, rispettivamente, di NGC752 (capitolo 5), di M35 & NGC2158 (capitolo 6) e di M67 (capitolo 7).

In the last years, the Observatory of Padova (Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Padova) and the University of Padova have been involved massively in projects dedicated to the exoplanets search, both ground, and space-based. SHARK-NIR, the acronym of “System for coronagraphy with High order Adaptive optics from R to K band – Near-Infrared”, is an instrument designed to search and characterize the young exo-planetary system and star-forming regions in the NIR domain, in coronagraphic direct imaging and spectroscopic mode. It has been selected for the 2nd generation Large Binocular Telescope (LBT) instruments, and it will take advantage of the excellent performance of the LBT adaptive optics system, which is delivering an eXtreme Adaptive Optics (XAO) correction, necessary for SHARK-NIR to achieve the best possible coronagraphic performance, which is mandatory to detect faint planets orbiting around bright stars. CHEOPS, the acronym of “CHaracterising ExOPlanet Satellite”, is the first mission dedicated to the characterization of small-size transiting planets using ultrahigh precision photometry on bright stars already known to host planets. It will allow an accurate determination of the radii of transiting planets, for which the mass has already measured from ground-based spectroscopic surveys. It will also provide precision radii for new planets discovered by the next generation of ground-based transits surveys (Neptune-size and smaller). PLATO, the acronym of “PLAnetary Transits and Oscillations of stars”, is a mission of Medium size satellites proposed for the European Space Agency in the program “Cosmic Vision”, with the target to detect and characterize exoplanets utilizing their transit on a bright star. The overall instrumental layout proposed by the Plato Payload Consortium consists of a multi-telescope concept instrument, composed by several tens of telescope units, for which it has developed an all-refractive optical solution. These devices are characterized by a very large Field of View (more than 20 degrees on one side) with an optical quality that fits most of the energy into a single sensor pixel. Such a goal can be achieved in a variety of solutions, some including aspheric elements as well. The activities concerning my Ph.D. have been exploited both in the framework of the space projects and in the field of ground instrumentation. For the PLATO project, I participated in the Assembly, Integration, and Verification (AIV) of the Telescope Optical Unit prototype, to validate the AIV procedure and the telescope optical performance in-flight conditions. Concerning SHARK, my activity has been performing optical alignment and qualification of the instrument.
L’Osservatorio di Padova (Istituto Nazionale di Astrofisica) e l’Università di Padova negli ultimi anni sono stati coinvolti massicciamente in progetti dedicati alla ricerca di pianeti extrasolari, sia con strumenti e telescopi da terra che dallo spazio. SHARK-NIR, che sta per “System for coronagraphy with High order Adaptive optics from R to K band – Near-Infrared”, è uno strumento disegnato per cercare e caratterizzare sistemi solari giovani e regioni di formazione stellare nel dominio di lunghezze d’onda del vicino infrarosso. La tecnica devota all’osservazione è quella spettroscopica e dell’immagine diretta. Questo strumento ottico è stato selezionato per la seconda generazione di dispositivi per il Large Binocular Telescope (LBT), con il vantaggio di sfruttare le eccellenti prestazioni del sistema di ottica adattiva di LBT. La correzione di ottica attiva estrema di LBT (XAO), è il requisito necessario di SHARK-NIR per ottenere la migliore cronografia attualmente disponibile con LBT ed è obbligatoria quando l’obiettivo è studiare pianeti poco luminosi che orbitano attorno a stelle brillanti. CHEOPS, che sta per “CHaracterising ExOPlanet Satellite”, è la prima missione spaziale dedicata alla caratterizzazione di piccoli pianeti già noti attorno a stelle brillanti tramite fotometria ad altissima precisione. Si otterranno accurate misure del raggio dei pianeti per i quali la massa è già nota da campagne spettroscopiche con telescopi da terra. Inoltre si conosceranno con precisione i raggi dei nuovi pianeti scoperti dalle campagne di osservazione da terra di nuova generazione basate sulla tecnica dei transiti, fino a pianeti di dimensioni di Nettuno o inferiori. PLATO, che sta per “PLAnetary Transits and Oscillations of stars”, è una missione proposta per il programma di nuovi satelliti di medie dimensioni “Cosmic Vision” dell’Agenzia Spaziale Europea. Il telescopio è focalizzato alla ricerca e caratterizzazione di eso-pianeti attorno a stelle brillanti e vicine al nostro Sole. Il progetto proposto dal consorzio PLATO consiste in un telescopio multiplo, composto da decine di telescopi singoli uguali, per i quali si è sviluppata una soluzione ottica totalmente rifrattiva. Ogni singolo telescopio ha un grande campo di vista (fino a 20 gradi) e una qualità ottica tale da concentrare la maggior parte dell’energia raccolta in un singolo elemento del sensore di immagini. Un tale scopo è raggiungibile applicando una molteplicità di soluzioni, tra cui anche l’uso di elementi ottici asferici. In questa tesi descriverò le attività svolte sia nell’ambito di un progetto spaziale che di uno strumento per telescopio a terra. Il progetto PLATO è stato trattato nell’ambito dell’integrazione, assemblaggio e verifica (AIV) del prototipo della singola unità ottica del telescopio, allo scopo di validare la procedura completa di AIV e le prestazioni in condizioni di volo. Riguardo lo strumento SHARK-NIR si spiegheranno le attività svolte per l’allineamento ottico e la qualificazione finale.

In der vorliegenden Arbeit werden Methoden der Erdsystemanalyse auf die Untersuchung der Habitabilität terrestrischer Exoplaneten angewandt. Mit Hilfe eines parametrisierten Konvektionsmodells für die Erde wird die thermische Evolution von terrestrischen Planeten berechnet. Bei zunehmender Leuchtkraft des Zentralsterns wird über den globalen Karbonat-Silikat-Kreislauf das planetare Klima stabilisiert. Für eine photosynthetisch-aktive Biosphäre, die in einem bestimmten Temperaturbereich bei hinreichender CO2-Konzentration existieren kann, wird eine Überlebenspanne abgeschätzt. Der Abstandsbereich um einen Stern, in dem eine solche Biosphäre produktiv ist, wird als photosynthetisch-aktive habitable Zone (pHZ) definiert und berechnet. Der Zeitpunkt, zu dem die pHZ in einem extrasolaren Planetensystem endgültig verschwindet, ist die maximale Lebenspanne der Biosphäre. Für Supererden, massereiche terrestrische Planeten, ist sie umso länger, je massereicher der Planet ist und umso kürzer, je mehr er mit Kontinenten bedeckt ist. Für Supererden, die keine ausgeprägten Wasser- oder Landwelten sind, skaliert die maximale Lebenspanne mit der Planetenmasse mit einem Exponenten von 0,14. Um K- und M-Sterne ist die Überlebensspanne einer Biosphäre auf einem Planeten immer durch die maximale Lebensspanne bestimmt und nicht durch das Ende der Hauptreihenentwicklung des Zentralsterns limitiert. Das pHZ-Konzept wird auf das extrasolare Planetensystem Gliese 581 angewandt. Danach könnte die 8-Erdmassen-Supererde Gliese 581d habitabel sein. Basierend auf dem vorgestellten pHZ-Konzept wird erstmals die von Ward und Brownlee 1999 aufgestellte Rare-Earth-Hypothese für die Milchstraße quantifiziert. Diese Hypothese besagt, dass komplexes Leben im Universum vermutlich sehr selten ist, wohingegen primitives Leben weit verbreitet sein könnte. Unterschiedliche Temperatur- und CO2-Toleranzen sowie ein unterschiedlicher Einfluss auf die Verwitterung für komplexe und primitive Lebensformen führt zu unterschiedlichen Grenzen der pHZ und zu einer unterschiedlichen Abschätzung für die Anzahl der Planeten, die mit den entsprechenden Lebensformen besiedelt sein könnten. Dabei ergibt sich, dass komplex besiedelte Planeten heute etwa 100-mal seltener sein müssten als primitiv besiedelte.
In this thesis methods of Earth system analysis are applied to the investigation of the habitability of terrestrial exoplanets. With the help of parameterized convection models for the Earth the thermal evolution of terrestrial planets is calculated. Under increasing central star luminosity the global carbonate-silicate cycle stabilizes the planetary climate. The life span of a photosynthetic-active biosphere existing in a certain temperature interval under adequate CO2 concentration is estimated. The range of orbital distances within which such a biosphere is productive is defined as the photosynthetic-active habitable zone (pHZ) and is calculated. The maximum life span of the biosphere is the point in time when the pHZ of an extrasolar planetary system finally disappears. For super-Earths, i.e. massive terrestrial planets, it is as longer as more massive the planet is and as shorter as more the planet is covered with continents. For super-Earths, which are not pronounced land or water worlds, the maximum life span scales with the planetary mass with an exponent of 0.14. The life span of the biosphere on a planet around K- or M-stars is always determined by the maximum life span and not limited by the end of the main-sequence evolution of the central star. The pHZ approach is applied to the extrasolar planetary system Gliese 581. Accordingly the super-Earth of 8 Earth masses Gliese 581d could be habitable. Based on the presented pHZ concept the Rare Earth Hypothesis established by Ward and Brownlee 1999 is quantified for the Milky Way. This hypothesis claims that complex life may be very rare in the Universe while primitive life is likely common and widespread. Different temperature and CO2 tolerances as well as a different influence on weathering of complex and primitive life forms result different boundaries of the pHZ and a different estimate of the number of planets potentially harboring these different life forms. It arises that planets with complex life might be 100 times rarer than primitive life bearing planets.

The study of magnetic fields on low-mass stars is important due to their ubiquity. They are responsible for phenomena spanning a wide range of spatial and temporal scales. Over the last two decades, the Zeeman-Doppler imaging (ZDI) technique has been used to study the topologies of stellar magnetic fields. A great deal has been learnt about how the magnetic characteristics of cool dwarfs vary as a function of parameters such as mass, rotation or age. In this thesis, I assemble a sample of stars with Zeeman-Doppler maps. I study their poloidal and toroidal components as a function of fundamental parameters and also in relation to activity cycles. I find that the relationship between poloidal and toroidal fields is different for stars above and below the fully convective boundary, in line with previous ZDI studies. I also find that the fields of strongly toroidal stars must be generated axisymmetrically. With regards to activity cycles, I find that so called “inactive branch" stars appear to remain poloidal throughout their activity cycle while so called “active branch" stars appear to be able to generate strong toroidal fields. Magnetic activity can also interact with exoplanets that may be orbiting a star. In this thesis, I consider two such interactions. The first is the compression of planetary magnetospheres by stellar winds. Sufficiently powerful winds can strip a planet of its atmosphere and render it uninhabitable. However magnetospheric shielding can provide some protection. I show that planets around 0.6 M⊙ - 0.8 M⊙ stars are the most likely to be able to protect their atmospheres. The second interaction I consider is exoplanetary radio emission. I present a wind model and show that exoplanetary radio emissions will depend strongly on the structure of the magnetic field structure of the central star.

The WASP project has discovered many transiting gas giant exoplanets. Some of these exoplanet systems have been observed by the K2 space-based telescope. The much higher photometric precision, shorter cadence and extended continuous follow-up observations provided by the K2 mission enabled the most detailed photometric characterization yet of the WASP and other planetary systems presented in this thesis, which contributes to our understanding of how planets form and evolve. I analysed the majority of transiting exoplanet systems observed by the K2 in the 1-min short-cadence mode within the first 14 regular observing campaigns. I present here the analysis and results for a total of 10 planetary systems observed in the short-cadence mode. I detected starspot occultation events in two aligned and one misaligned planetary system and proved that detecting starspot occultation events is possible in the K2 data. I also detected optical phase-curve modulations in two systems, rotational modulations in four and γ Doradus pulsations in one planetary system. I refined the system parameters for all short-cadence targets and used non-detections to provide tight upper limits. In addition, I discovered a hot Jupiter using the long-cadence K2 data and refined the ephemeris with the WASP data of another K2-discovered planet.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 179-182).
Biosignature gases in the atmosphere of an exoplanet provide a means by which we can deduce the possible existence of life on that planet. As the list of possible biosignature gases is ever growing, the need to determine which molecules provide the best opportunities for detection grows as well. One way to explore these systems is through modeling radiative transfer via transmissivity as light travels from the parent star, through the atmosphere of the planet, and then impacts a detector located at Earth. As the light travels through the planetary atmosphere, it acquires molecular features from the planet due to the composition, temperature, and pressure structure of the atmosphere. By adding synthetic noise to the modeled transmissivity spectra, I determine the detectability of a range of atmospheric mixing ratios for ten biosignature gases from the HIgh-resolution TRANsmission molecular absorption (HITRAN) database: oxygen, ozone, methane, nitrous oxide, methyl bromide, methyl chloride, hydrogen sulfide, carbonyl sulfide, phosphine, and sulfur dioxide. The deep investigation of the HITRAN biosignature gases in this study is possible due to the ability to properly map their absorption cross sections to varying temperatures and pressures. For each of the above HITRAN molecules, I analyze alternative spectral features for detection in order to emphasize the importance of and determine the ability for multiple band detection of biosignature gases. Water vapor (though not a biosignature gas) is included in order to study its potential for spectral masking. Though I nd that each of the above HITRAN gases could be detected in exoplanet atmospheres if that molecule has a large enough atmospheric mixing ratio, an Earthsize planet with an Earth-like atmosphere located at 35.45 parsecs would only allow for discernible biosignature features from ozone, nitrous oxide, and methane in the infrared wavelength region. Sixteen additional (and non-standard) biosignature gases included in this study do not have absorption cross sections that are currently mapable to alternative temperatures and pressures. These sixteen biosignature gases are acetaldehyde, acetone, benzene, carbon disulfide, dimethyl disulfide, dimethyl sulfide, dimethyl sulfoxide, ethanol, ethyl mercaptan, fluoroacetone, isoprene, methyl ethyl ketone, methyl mercaptan, methyl vinyl ketone, thioglycol, and toluene. To circumvent the nonmapability of the absorption cross sections to dierent temperatures and pressures, I use the detectivity calculations and the absorption cross sections from ozone, methane, and nitrous oxide to estimate the threshold atmospheric mixing ratios for the detection of the sixteen non-standard biosignature gases with a 35 m telescope, 100 hours of observation, and a target distance of 35.45 parsecs. The combination of the threshold atmospheric mixing ratios calculated for these sixteen non-standard biosignature gases with the results from the HITRAN biosignature gases investigated in this study demonstrate that an atmospheric gas will require a mixing ratio in the tens to hundreds of ppm to be detectable above a 5[sigma] level with a 35 m telescope, an observation time of 100 hours, and a target distance of 35.45 parsecs. Keeping with the theme of multi-wavelength detection, I end the analysis of the sixteen non-standard biosignature gases by proposing potential spectral feature wavelengths for each gas based on their molecular absorption cross section spectral profiles. As many biosignature gases have molecular features at longer wavelengths than the traditional IR region, I investigated the technological requirements for detecting biosignature gas spectral features in one of the low-signal long-wavelength regions, the millimeter. Though the investigation into the millimeter region reveals unrealistic technological demands for the successful detection of the case study, oxygen, I use the analysis as a platform to introduce the theoretical concept of observing future targets with multiple next-generation telescopes stationed in a matrix in order to produce the same observational ability of a larger (and more distant future) telescope. While interferometric investigations into millimeter spectral features are improbable in the near future, the use of interferometry with next generation instruments may allow for investigations in the 10 - 30 [mu]m region, thereby opening alternative wavelengths for biosignature gas detection. Since this theoretical interferometry idea relies on the ability to increase the signal-to-noise ratio (SNR) of the observations, I investigated the interaction between telescope aperture size and observation duration on the detectability (i.e. SNR) of biosignature gases in reference to finding a middle ground between these two system parameters for both a 6 m and 35 m telescope. Unfortunately, a 6 m telescope does not provide a large enough collecting area to increase the SNR sufficiently enough to detect atmospheric gases. For futuristic telescope designs, though a 20 m telescope (or nine JWSTs working together to achieve the same collecting area) would begin to discern some biosignature gas features from the continuum (for high biosignature gas atmospheric abundances), a 35 m class telescope (or equivalent interferometric telescope array) should be the minimum aperture size considered for biosignature gas detection in transmissivity spectroscopy.
by Stephen Joseph Messenger.
S.M.

The field of transiting extrasolar planets and especially the study of their atmospheres is one of the youngest and most dynamic subjects in current astrophysics. To study the atmospheres of those foreign worlds, we typically require a 10^−4 to 10^−5 level of accuracy in flux. Currently available instruments were not designed with these precisions in mind. Calibrating an instrument without knowing its response function at the required level has become the central challenge of exoplanetary spectroscopy. A variety of parametric correction models are used in the literature. These show high degeneracies between the scientific result and the instrument correction used. Hence, an unbiased analysis of the data at the 10^−4 level of accuracy is difficult and the cause of much controversy in the field. In this thesis, I present three novel ways of de-trending exoplanetary data non-parametrically, i.e. without requiring auxiliary or prior information of the instrument or data. This removes correctional bias. These techniques are based on: 1) unsupervised machine-learning algorithms (Chapter 3) to de-convolve non-Gaussian sig- nals, i.e. the systematic noise, from the desired astrophysical feature. Such a ‘blind’ signal de-mixing is commonly known as the ‘Cocktail Party problem’ in signal-processing. I demon- strate its capabilities using spectroscopic Hubble/NICMOS measurements of the hot-Jupiters HD189733b and XO1b and demonstrate the removal of stellar noise in Kepler photometry (Chapter 4). 2) Fourier/Wavelet based self-filtering algorithms based on the concepts of sparsity of the exoplanetary signal in the frequency domain (Chapter 5). The robustness of this method is demonstrated for very low signal-to-noise conditions using four nights of ground-based observa- tions of the secondary eclipse of HD189733b in Chapter 6. Here I unambiguously confirm the detection of a strong non-LTE methane emission in the L-band and can test for residual telluric contamination using this method. 3) an Independent-component-analysis supported wavelet masking of multivariate data, which extends the non-parametric machine learning to Gaussian noise dominated data applications, Chapter 7. In the light of ever increasing data analysis challenges, as we probe ever smaller signals and fainter targets, techniques such as the ones presented in this thesis are paramount to the success of exoplanetary characterisation in the future.

We have used the Spitzer Space Telescope to observe two transiting planetary systems orbiting low-mass stars discovered in the Kepler K2 mission. The system K2-3 (EPIC 201367065) hosts three planets, while K2-26 (EPIC 202083828) hosts a single planet. Observations of all four objects in these two systems confirm and refine the orbital and physical parameters of the planets. The refined orbital information and more precise planet radii possible with Spitzer will be critical for future observations of these and other K2 targets. For K2-3b we find marginally significant evidence for a transit timing variation between the K2 and Spitzer epochs.

Host star metallicity provides a measure of the conditions in protoplanetary disks at the time of planet formation. Using a sample of over 20,000 Kepler stars with spectroscopic metallicities from the LAMOST survey, we explore how the exoplanet population depends on host star metallicity as a function of orbital period and planet size. We find that exoplanets with orbital periods less than 10 days are preferentially found around metal-rich stars ([Fe/H] similar or equal to 0.15 +/- 0.05 dex). The occurrence rates of these hot exoplanets increases to similar to 30% for super-solar metallicity stars from similar to 10% for stars with a sub-solar metallicity. Cooler exoplanets, which reside at longer orbital periods and constitute the bulk of the exoplanet population with an occurrence rate of greater than or similar to 90%, have host star metallicities consistent with solar. At short orbital periods, P < 10 days, the difference in host star metallicity is largest for hot rocky planets (< 1.7 R-circle plus), where the metallicity difference is [Fe/H] similar or equal to 0.25 +/- 0.07 dex. The excess of hot rocky planets around metal-rich stars implies they either share a formation mechanism with hot Jupiters, or trace a planet trap at the protoplanetary disk inner edge, which is metallicity dependent. We do not find statistically significant evidence for a previously identified trend that small planets toward the habitable zone are preferentially found around low-metallicity stars. Refuting or confirming this trend requires a larger sample of spectroscopic metallicities.

The discovery of exoplanets represents one of the greatest scientific revolutions in history, and exoplanetary science has rapidly become uniquely positioned to address profound questions about the origins of life, and about humanity's place (and future) in the cosmos. Since the discovery of the first exoplanet over two decades ago, the radial velocity (RV) method has been one of the most productive techniques for discovering new planets. It has also become indispensable for characterising exoplanets detected via other techniques, notably transit photometry. Unfortunately, signals intrinsic to stars themselves - especially magnetic activity signals - can induce RV variations that can drown out or even mimic planetary signals. Modelling and thus mitigating these signals is notoriously difficult, which represents a major obstacle to using next-generation instruments to detect lower mass planets, planets with longer periods, and planets around more magnetically-active stars. Enter Gaussian processes (GPs), which have a number of features that make them very well suited to the joint modelling of stochastic activity processes and dynamical (e.g. planetary) signals. In this thesis, I leverage GPs to enable the study of smaller planets around a wider variety of stars than has previously been possible. In particular, I develop a principled and sophisticated Bayesian framework, based on GPs, for modelling RV time series jointly with ancillary activity-sensitive proxies, thus allowing activity signals to be constrained and disentangled from genuine planetary signals. I show that my framework succeeds even in cases where existing techniques would fail to detect planets, e.g. the case of a weak planetary signal with period identical to its host star's rotation period. In a first application of the framework, I demonstrate that Alpha Centauri Bb - until 2016, thought to be the closest exoplanet to Earth, and also the lowest minimum-mass exoplanet around a Sun-like star - was, in fact, an astrophysical false positive. Next, I use the framework to re-characterise the well-studied Kepler-10 system, thereby resolving a mystery surrounding the mass of planet Kepler-10c. I also use the framework to help discover or characterise various exoplanets. Finally, the activity modelling framework aside, I also present in outline form a few promising applications of GPs in the context of modelling stellar signals and studying exoplanets, viz. GPs for (i) enhanced characterisation of stellar rotation; (ii) generating realistic synthetic observations, and modelling in a systematic way the effects of an observing window function; and (iii) ultra-precise extraction of RV shifts directly from observed spectra, without requiring template cross-correlation.

Nous cherchons à mettre en évidence l'influence des hétérogénéités de température, de structure ou de composition des atmosphères sur leurs observations. Dans le années à venir, de plus en plus d'appareils vont permettre l'observation par transmission des atmosphères d'exoplanètes. Toutefois, les outils numériques permettant de contraindre ces dernières reposent sur des modèles simples à une dimension. Ils supposent en effet des atmosphères ne possédant qu'une structure verticale (le climat est le même en tout point de la surface, la composition ou la température n'évolue qu'avec l'altitude). Cette approche a le mérite de permettre des calculs rapides et de contraindre les paramètres globaux de l'atmosphère avec des temps raisonnables. Ceci ne serait pas possible en l'état avec une modélisation en 3 dimensions des atmosphères, même si ce serait beaucoup plus réaliste. Ce que nous cherchons à mettre en évidence, ce sont les limites des techniques actuelles d'inversion et donc, de caractérisation des atmosphères qui seront observées. Pour cela, il fallait mettre au point un logiciel capable de résoudre le transfert radiatif au sein d'une atmosphère en 3 dimensions (et non plus 1 seul). Une fois le logiciel terminé, nous avons éprouvé l'algorithme de traitement du signal TauREx en comparant les résultats qu'il proposait à des simulations atmosphériques parfaitement contrôlées. Nous nous sommes tout principalement arrêté sur les biais découlant d'hétérogénéités de température en simulant des atmosphères avec un fort contraste jour/nuit. Ceci nous a permis de caractériser les biais découlant de ces types d'hétérogénéités, de les quantifier et de mettre l'accent sur un biais jusqu'ici très sous-estimé par la communauté, à savoir celui découlant des hétérogénéités le long de la ligne de visée. Nous avons appuyé nos propos et concentré nos efforts sur l'interprétation de l'inversion d'une simulation complexe de l'atmosphère de GJ 1214 b. La reconstitution de la chaine observationnelle : GCM (LMD), Pytmosph3R (LAB) et TauREx (UCL) ouvre les portes d'un vaste panel d'études envisageables, et notamment tout ce qui va concerner l'identification et la caractérisation des biais systématiques qui incomberont les observations à venir
Transmission spectroscopy provides us with information on the atmospheric properties at the limb, which is often intuitively assumed to be a narrow annulus aound ther planet. Consequently, the few recent studies on the effect of atmospheric horizontal heterogeneities on transmission spectra have used approaches sensitive to variations along the limb only. Here we demonstrate that the region probed in transmission – the limb – actually extends significantly toward the day and night sides of the planet. Consequently we show that thestrong day-night thermal and compositional gradients expected on synchronous exoplanets create sufficient heterogeneities across the limb to result in important systematic effects on the spectrum and bias its interpretation. To quantify these effects, we developed a 3D radiative transfer model able to generate transmission spectra of atmospheres based on 3D atmospheric structures, whether they come from a Global Climate Model or more parametrized models. We first apply this tool to a simulation of the atmosphere of GJ 1214 b toproduce synethic JWST observations and show that producing a spectrum using only atmospheric columns at the terminator results in errors greater than expected noise. This demonstrates the necessity of a real 3D approach to model data for such precise observatories.Second, we investigate how day-night temperature gradients cause a systematic bias in retrieval analysis performed with 1D forward models. For that purpose we synthesize a large set of forward spectra for prototypical HD209458 b and GJ 1214 b type planets varying the temperatures of the day and night sides as well as the width of the transition region. We then perform typical retrievalanalyses and compare the retrieved parameters to the ground truth of the input model. This study reveals systematic biases on the retrieved temperature (found to be higher than the terminator temperature) and absorber abundances. This is due to the fact that the hotter dayside is more extended vertically and screens the nightside—a result of the nonlinear properties of atmospheric transmission.These biases will be difficult to detect as the 1D profiles used in the retrieval procedure are found to provide an excellent match to theobserved spectra based on standard fitting criteria (chi2, posterior distributions). This fact needs to be kept in mind when interpretingcurrent and future data

This thesis presents studies of transiting exoplanets using observations gathered in large part from space, with the NASA EPOXI Mission, the Spitzer Space Telescope, and the Kepler Mission. The first part of this thesis describes searches for additional transiting planets in known exoplanet systems, using time series photometry gathered as part of the NASA EPOXI Mission. Using the EPOXI light curves spanning weeks for each star, we searched six exoplanetary systems for signatures of additional transiting planets. These six systems include five hosts to hot Jupiters: HAT-P-4, TrES-3, TrES-2, WASP-3, and HAT-P-7, and one host to a hot Neptune: GJ 436. We place upper limits on the presence of additional transiting planets in the super-Earth radius range for GJ 436 in Chapter 2, and in the Neptune-to-Saturn radius range for the other five systems in Chapter 4. Chapter 3 details a search for additional transits of a hypothesized planet smaller than the Earth, whose presence was suggested by the EPOXI observations of GJ 436. In that study, we demonstrate the sensitivity of Warm Spitzer observations to transits of a sub-Earth-sized planet. The fifth chapter details the characterization and validation of the Kepler-19 system, which hosts a transiting 2.2 \(R_{\bigoplus}\) planet, Kepler-19b. We demonstrate the planetary nature of the transit signal with an analysis that combines information from high-resolution spectroscopy, the shape of the transit light curve, adaptive optics imaging, and near-infrared transits of the planet. The sinusoidal variation in the transit times of Kepler-19b indicates the presence of an additional perturbing body, and comprises the first definitive detection of a planet using the transit timing variation method. While we cannot uniquely determine the mass and orbital period of Kepler-19c, we establish that its mass must be less than 6 times the mass of Jupiter. The sixth chapter presents evidence for the validation of a 2.0 \(R_{\bigoplus}\) planet residing in the habitable zone of a low-mass star, Kepler Object of Interest 1361.01. We discuss the theoretical composition of the planet, and address issues specific to habitability of planets orbiting M dwarfs.
Astronomy

Дана робота присвячена дослідженню процесу в області пошуку та вивчення екзопланет - планетарних утворень поза межами нашої сонячної системи. В роботі також детально розглянуто фізичні основи методик пошуку екзопланет. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/14082

Thesis (Ph.D.)--Boston University
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This dissertation presents the legacy, theory, design, characterization, and application prospects of a fully symmetric monolithic nulling interferometer (nuller). A nuller's function is to destructively interfere light originating from a bright, on-axis, unresolved source in order to lower its contrast with faint, off-axis sources of light in the field of view. The primary application lies in astronomical instrumentation, serving as an enabling technology for directly imaging exoplanets and measuring exozodiacal dust and debris disks, the planetary system evolutionary components around nearby stars. Typical on-sky planet/star flux ratios are 1:109 or less in the visible. Mitigating this contrast is key to spectroscopic study of exoplanets, which aims to characterize exoplanetary atmospheres and potentially locate biosignatures on exo-Earths. Within the past decade, adaptive optics-equipped breadboard demonstrations of nullers and other coronagraphs have shown the capability to image nearby (< 30 lightyears) extrasolar analogs to Jupiter with a 0.5 meter diameter telescope in the visible. The quiet laboratory environments that have been produced to demonstrate this capability do not reflect those of typical ground-based observatories where thermal drifts perturb optical alignment and atmospheric turbulence perturbs the source wavefront. Space-based platforms circumvent the atmosphere problem, but are still subjected to thermal instabilities and their associated risks. Robust optical systems must be designed and flight-tested in order to address such risks and provide grounds for their inclusion in the design of future exo-Earth imaging satellites. Sub-orbital platforms such as sounding rockets and high-altitude balloons provide a rapid, lowcost means of providing heritage for such optical systems while also delivering significant scientific results. The primary risk inherent with these platforms are harsh transient environmental conditions, for which, similar to an orbital platform, robust optical systems are necessary. A novel feature of the nuller described in this work is its monolithic design, which greatly enhances optical stability, the primary obstacle plaguing all high-contrast imaging efforts. Additional design benefits include theoretical achromatic performance and an inner working angle that is 2-4 times smaller than other coronagraph designs, enabling its use with proportionally smaller telescopes.
2031-01-01

This dissertation investigates two stellar systems known to contain extrasolar planets. It is comprised of five chapters that are readily divided into three independent but related analyses. Chapter 1 reports on the analysis of low signal-to-noise secondary-eclipse observations of the Neptune-sized exoplanet GJ 436b using the Spitzer Space Telescope in multiple infrared channels. The measured wavelength-dependent eclipse depths provide constraints on the planet's dayside atmospheric composition and thermal profile. The analysis indicates that GJ 436b's atmosphere is abundant in carbon monoxide and deficient in methane relative to thermochemical equilibrium models for the predicted hydrogen-dominated atmosphere. Chapter 2 discusses the techniques used to analyze GJ 436b, introduces the Least Asymmetry centering method and compares its effectiveness to two existing techniques, and describes the functions used to model Spitzer's position- and time-dependent systematics. Additionally, it includes best-fit parameters with uncertainties, histograms of the free parameters, and correlation plots between free parameters. Chapter 3 reports on the analysis of eleven HD 149026b secondary-eclipse observations at five Spitzer wavelengths plus three primary-transit observations at 8.0 microns. Chemical-equilibrium models find no indication of a temperature inversion in the dayside atmosphere of HD 149026b. The best-fit model favors large amounts of CO and CO2, moderate heat redistribution (f = 0.5), and a strongly enhanced metallicity. These analyses use BiLinearly-Interpolated Subpixel Sensitivity (BLISS) mapping and parameter orthogonalization. The former is a new technique to model two position-dependent systematics, intrapixel variability and pixelation. The latter is a technique that accelerates the convergence of Markov chains that employ the Metropolis random walk sampler. Chapter 4 reports on the detection of GJ 436c, a 0.65 +/- 0.04 Earth-radii exoplanet transiting a nearby M-dwarf star with a period of 1.365862 +/- 8x10^{-6} days. It also presents evidence for a similarly sized exoplanet candidate (currently labeled UCF-1.02) orbiting the same star with an undetermined period. Assuming an Earth-like density of 5.515 g/cm^{3}, GJ 436c has a predicted mass of 0.28 Earth-masses (2.6 Mars-masses) and a surface gravity of 0.65 g (where g is the gravity on Earth). Its weak gravitational field and close proximity to its host star imply that GJ 436c is unlikely to have retained its original atmosphere; however, a transient atmosphere is possible if recent impacts or tidal heating were to supply volatiles to the surface. Chapter 5 presents numerical simulations of the GJ 436 system using the Mercury N-body integrator and detailed calculations used to constrain the atmospheric composition of the sub-Earth-sized planet GJ 436c. The simulations find a ~35-year periodic trend in the osculating elements wherein GJ 436c's eccentricity varies between 0 and 0.21, its peak-to-trough inclination amplitude is 3.2 degrees, and transit-timing variations range from +/-200 to +/-3 minutes.
Ph.D.
Doctorate
Physics
Sciences
Physics; Planetary Sciences

We propose a new method for detecting exoplanets using gravita-tional lensing. The hypothesis is that the lensing caused by an exo-planet could distort the structures of a radio background, for instancea H II region. It cannot be done with todays telescope but with thesecond incarnation of the Square Kilometer Array (SKA), currently inits design phase we deem it possible. In order to test this hypothesis weconstructed a simulation that creates a simple background structurewith variable scale and then produces simulated images such as theones achievable with the SKA. We produce positive result with a clearsignature of the planet with certain background scales and suggestfurther investigation into this method of detecting exoplanets.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 269-304).
The endeavor to characterize terrestrial exoplanets warrants the study of chemistry in their atmospheres. Here I present a comprehensive one-dimensional photochemistry-thermochemistry model developed from the ground up for terrestrial exoplanet atmospheres. With modern numerical algorithms, the model has desirable features for exoplanet exploration, notably the capacity to treat both thin and thick atmospheres ranging from reducing to oxidizing, and to find steady-state solutions starting from any reasonable initial conditions. These features make the model the first photochemistry-thermochemistry model applicable for non-hydrogen-dominated thick atmospheres on terrestrial exoplanets. Using the photochemistry model, I explore the compositions of thin atmospheres on terrestrial exoplanets controlled by surface emission and deposition of gases. Highlights of my findings are: (1) oxygen and ozone may build up in 1-bar CO2 atmospheres to levels that have conventionally been accepted as unique signatures of life, if there is no surface emission of reducing gases; (2) volcanic carbon compounds (CH4 and CO2) are likely to be abundant in terrestrial exoplanet atmospheres; but volcanic sulfur compounds (H2S and SO2) are chemically short-lived and therefore cannot accumulate in virtually any types of terrestrial exoplanet atmospheres. Also using the photochemistry model, I explore the ranges of molecular compositions of thick atmospheres on terrestrial exoplanets. I find that carbon has to be in the form of CO2 in a H2-depleted water-dominated atmosphere, and that the preferred loss of light elements from an oxygen-poor and carbon-rich atmosphere leads to formation of unsaturated hydrocarbons (C2H2 and C2H4). These results imply that chemical stability has to be taken into account when interpreting the spectrum of a super Earth/mini Neptune like GJ 1214b. Another intriguing category of terrestrial exoplanets is bare-rock exoplanets. I present the first theoretical framework to compute disk-integrated spectrum from a bare-rock exoplanet, taking into account the reflectivity and emissivity of solid minerals on the surface. I find that silicate surfaces lead to prominent spectral features in the 8 - 13 [mu]m range, detectable by mid-infrared spectroscopy using transit. Therefore transit spectroscopy is an independent method to confirm the rocky nature of an exoplanet.
by Renyu Hu.
Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 197-205).
Insights into a distant exoplanet's interior are possible given a synergy between models and observations. Spectral observations of a star's radial velocity wobble induced by an orbiting planet's gravitational pull measure the planet mass. Photometric transit observations of a planet crossing the disk of its star measure the planet radius. This thesis interprets the measured masses and radii of super-Earth and sub-Neptune exoplanets, employing models to constrain the planets' bulk compositions, formation histories, and habitability. We develop a model for the internal structure of low-mass exoplanets consisting of up to four layers: an iron core, silicate mantle, ice layer, and gas layer. We quantify the span of plausible bulk compositions for low-mass transiting planets CoRoT-7b, GJ 436b, and HAT-P-11b, and describe how Bayesian analysis can be applied to rigorously account for observational, model, and inherent uncertainties. We present a detailed case study of GJ 1214b, the first exemplar of a new class of volatile-rich super-Earth exoplanets. At 6.5 Mo and 2.7 Ro, GJ 1214b must have a gas layer to account for its low mean density. We present three possible scenarios for the origin of the gas layer on GJ 1214b: direct accretion of H/He gas from the protoplanetary nebula, sublimation of ices, and outgassing of volatiles from a rocky interior. We next explore the low-density extreme of the mass-radius relations for volatilerich super-Earth exoplanets. Using models of planet formation, structure, and survival, we constrain the minimum plausible planet mass for a measured planet radius and equilibrium temperature. We explore both core-nucleated accretion and outgassing as two separate formation pathways for Neptune-size planets with voluminous atmospheres of light gases. Finally, we present a practical method to assess whether a hydrogen-rich sub-Neptune planet with measured mass and radius could potentially harbor a liquid water ocean. Using a one-dimensional radiative-convective model of energy transport through water-saturated hydrogen-rich envelopes, we constrain the combinations of planet properties (mass, radius, equilibrium temperature, intrinsic luminosity) that are conducive to liquid water oceans. The pace of low-mass exoplanet discoveries is poised to accelerate, and this thesis will contribute to constraining the interior properties of newfound planets.
by Leslie Anne Rogers.
Ph.D.