Academic literature on the topic 'Exoplanets'

Resumo: Este trabalho investigou os resultados e impactos de atividades de divulgação científica sobre a ciência dos exoplanetas, ocorridas em 2018, junto a alunos de quatro escolas de educação básica situadas em municípios do litoral norte paulista. Essas ações permitiram que os alunos adquirissem melhor compreensão acerca dos conceitos apresentados sobre exoplanetas e procuraram incentivar o aprofundamento no estudo de áreas da astronomia. Para a elaboração das apresentações estudou-se tanto o estado atual dos conhecimentos científicos sobre exoplanetas, quanto o modo como o trabalho didático com temas de astronomia pode ser efetuado a alunos dos ensinos fundamental e médio. Nas apresentações foram usados diferentes recursos que procuraram tornar mais compreensíveis os conceitos científicos envolvidos e as técnicas de detecção de exoplanetas. Em particular, considerou-se o caráter interdisciplinar da ciência dos exoplanetas, bem como, conhecimentos relacionados à história da astronomia.Palavras-chave: Astronomia; Ensino de Física; Divulgação da Ciência; Detecção de Exoplanetas. Scientific dissemination activities on exoplanetsAbstract: This work investigated the results and impacts of scientific dissemination activities on the science of exoplanets, which took place in 2018, with students from four schools of basic education located in municipalities on the north coast of São Paulo. These actions allowed students to gain a better understanding of the concepts presented about exoplanets and sought to encourage further study in areas of astronomy. For the elaboration of the presentations, it was studied both the current state of the existing scientific knowledge about exoplanets, as well as the way the didactic work with astronomy themes can be carried out with elementary and high school students. In the presentations, different resources were used to make the scientific concepts involved and the techniques for detecting exoplanets more understandable. In particular, the presentations considered the interdisciplinary nature of the science of exoplanets, as well as knowledge related to the history of astronomy.Keywords: Astronomy; Physics Teaching; Dissemination of Science; Exoplanet Detection.

Context. The magnetized wind from stars that impact exoplanets should lead to radio emissions. According to the scaling laws derived in the solar system, the radio emission should depend on the stellar wind, interplanetary magnetic field, and topology of the exoplanet magnetosphere. Aims. The aim of this study is to calculate the dissipated power and subsequent radio emission from exoplanet magnetospheres with different topologies perturbed by the interplanetary magnetic field and stellar wind, to refine the predictions from scaling laws, and to prepare the interpretation of future radio detections. Methods. We use the magnetohydrodynamic (MHD) code PLUTO in spherical coordinates to analyze the total radio emission level resulting from the dissipation of the kinetic and magnetic (Poynting flux) energies inside the exoplanet’s magnetospheres. We apply a formalism to infer the detailed contribution in the exoplanet radio emission on the exoplanet’s day side and magnetotail. The model is based on Mercury-like conditions, although the study results are extrapolated to exoplanets with stronger magnetic fields, providing the lower bound of the radio emission. Results. The predicted dissipated powers and resulting radio emissions depend critically on the exoplanet magnetosphere topology and interplanetary magnetic field (IMF) orientation. The radio emission on the exoplanet’s night and day sides should thus contain information on the exoplanet magnetic field topology. In addition, if the topology of an exoplanet magnetosphere is known, the radio emission measurements can be used as a proxy of the instantaneous dynamic pressure of the stellar wind, IMF orientation, and intensity.

Abstract A stable-frequency transmitter with relative radial acceleration to a receiver will show a change in received frequency over time, known as a “drift rate.” For a transmission from an exoplanet, we must account for multiple components of drift rate: the exoplanet’s orbit and rotation, the Earth’s orbit and rotation, and other contributions. Understanding the drift rate distribution produced by exoplanets relative to Earth, can (a) help us constrain the range of drift rates to check in a Search for Extraterrestrial Intelligence project to detect radio technosignatures, and (b) help us decide validity of signals-of-interest, as we can compare drifting signals with expected drift rates from the target star. In this paper, we modeled the drift rate distribution for ∼5300 confirmed exoplanets, using parameters from the NASA Exoplanet Archive (NEA). We find that confirmed exoplanets have drift rates such that 99% of them fall within the ±53 nHz range. This implies a distribution-informed maximum drift rate ∼4 times lower than previous work. To mitigate the observational biases inherent in the NEA, we also simulated an exoplanet population built to reduce these biases. The results suggest that, for a Kepler-like target star without known exoplanets, ±0.44 nHz would be sufficient to account for 99% of signals. This reduction in recommended maximum drift rate is partially due to inclination effects and bias toward short orbital periods in the NEA. These narrowed drift rate maxima will increase the efficiency of searches and save significant computational effort in future radio technosignature searches.

Abstract The discovery of planets around stars other than Sun was a grand milestone to understand origin and evolution of life in Universe. 2019 Nobel Prize for Physics was awarded to the first discovery of exoplanet around Sun-like stars, Peg 51b, in 1995. With development of 25 years, the current number of confirmed exoplanets have reached 4,000. The population of exoplanets presents great diversity and complexity beyond the planets in Solar system, severely challenging our understanding on the origin and evolution of planets. Moreover, clues of extrasolar life have been partially disclosed by detection of exoplanets in habitable zone with temporal surface temperature. In recent years, several promising surveys of exoplanets have been carried out to search for more exoplanets, compiling more complete sample of exoplanets and detecting Earth-like exoplanets. Transiting Exoplanet Survey Satellite (TESS) launched in 2018, is the most import facility for this purpose. It monitors the brightness of nearby stars in all sky with high cadences, searching for exoplanetary transit events. The survey is sensitive to detect terrestrial exoplanets. In this work, we reanalyzed the high quality light curves of TESS with algorithm developed by ourselves and visual examination. Our work was designed complementary to the automatic pipeline developed by TESS science team. TESS pipeline is not optimal for long-period exoplanets, for which only one transit event occurring in the observation sectors of 27.4 days, appearing as single transit single. Those long-period planets are more likely to be habitable with liquid water on their surface in relative large orbits. We took efforts to recover exoplanets with single transit in TESS. First, we identified candidates with significant narrow dimming in light curves uniformly by our automatic program. The singles were further examined visually and fitted by transit profile, selecting transit events. More precise modeling was carried out by MCMC analysis for transit exoplanet candidates. As a preliminary attempt, we only processed the light curves in sector 1 only. Full TESS dataset in all 26 sectors will be studied in future. In summary, we detected 25 exoplanet candidates in publicly accessible light curves in TESS sector 1. Among them, 14 candidates are known exoplanets, and 6 are candidates identified by TESS pipeline in catalog of Tess Objects of Interest (TOI). 5 exoplanet candidates with single transit signal are newly identified by their profiles, and the properties of these system were inferred in this work. The orbital parameters and physical properties derived by us are consistent with those in literature for all the 14 known exoplanets. 2 among 6 of exoplanet candidates in TOI catalog are single transit objects, our results are consistent with values reported in TOI catalog. For the new exoplanet candidates, we report their inferred orbits and physical sizes. We plan to implement our analysis for all light curves in 26 sectors of TESS, Over 100 exoplanet candidates are expected to be recovered, significantly contributing to the current population of 4,000 known exoplanets.

Context. Mass and radius are two fundamental properties for characterising exoplanets, but only for a relatively small fraction of exoplanets are they both available. Mass is often derived from radial velocity measurements, while the radius is almost always measured using the transit method. For a large number of exoplanets, either the radius or the mass is unknown, while the host star has been characterised. Several mass-radius relations that are dependent on the planet’s type have been published that often allow us to predict the radius. The same is true for a bayesian code, which forecasts the radius of an exoplanet given the mass or vice versa. Aims. Our goal is to derive the radius of exoplanets using only observables extracted from spectra used primarily to determine radial velocities and spectral parameters. Our objective is to obtain a mass-radius relation independent of the planet’s type. Methods. We worked with a database of confirmed exoplanets with known radii and masses, as well as the planets from our Solar System. Using random forests, a machine learning algorithm, we computed the radius of exoplanets and compared the results to the published radii. In addition, we explored how the radius estimates compare to previously published mass-radius relations. Results. The estimated radii reproduces the spread in radius found for high mass planets better than previous mass-radius relations. The average radius error is 1.8 R⊕ across the whole range of radii from 1–22 R⊕. We find that a random forest algorithm is able to derive reliable radii, especially for planets between 4 R⊕ and 20 R⊕ for which the error is under 25%. The algorithm has a low bias yet a high variance, which could be reduced by limiting the growth of the forest, or adding more data. Conclusions. The random forest algorithm is a promising method for deriving exoplanet properties. We show that the exoplanet’s mass and equilibrium temperature are the relevant properties that constrain the radius, and do so with higher accuracy than the previous methods.

Exoplanets are planets orbiting a star other than the Sun. These exoplanets may exist in many different forms, such as a hot Jupiter and super earth. Detecting is the first step to further studying the properties of these exoplanets. In this paper, based on data of star Qatar-1 gathered from July 22nd 2022, a light flux curve is developed during the period of 04:28 - 07:01 UTC through which the star is observed. The presence of an exoplanet, presumably Qatar-1b, is revealed in the analyzing results of the collected data, showing the validity of the transit approach for exoplanet detection. By using this approach, exoplanets planets can be discovered for further research in regards to potentially habitable and/or resource-rich exoplanets.

An exoplanet is a planet that orbits a star outside of our solar system. The study of exoplanets is an active area of research in astronomy. In this research, we aim to utilize the Kepler dataset provided by NASA EXOPLANET ACRCHIEVE to identify and classify exoplanets that could potentially support life. The Kepler dataset, which comprises of observations of over 150,000 stars, has been instrumental in the discovery of thousands of exoplanets. We will analyse the dataset using machine learning techniques to classify exoplanets as potentially habitable based on their orbital period, size, distance from their host star, and other parameters. The findings of this research will greatly enhance our understanding of the frequency of life in the universe and the use of machine learning techniques on the Kepler dataset will be an essential tool in the quest for finding potentially habitable exoplanets. Emerging Machine Learning Algorithms aid in detecting habitability of exoplanet in different stellar system. For finding an Exoplanet we have used the transit method which is based on the principle that when an exoplanet passes in front of its host star, it causes a temporary dip in the star's brightness. By monitoring the brightness of a star over time, scientists can detect these periodic dips and use them to infer the presence of an exoplanet. The findings of this research have the potential to significantly advance our understanding of the prevalence of life in the universe.

Abstract As radio astronomy enters a golden age, ground-based observatories are reaching sensitivities capable of unlocking a new and exciting field of exoplanet observation. Radio observation of planetary auroral emission provides unique and complementary insight into planetary science not available via orthodox exoplanet observation techniques. Supplying the first measurements of planetary magnetic fields, rotation rates, and orbital obliquities, we gain necessary and crucial insight into our understanding of the star–planet relationships, geophysics, composition, and habitability of exoplanets. Using a stellar-wind-driven Jovian approximation, we present analytical methods for estimating magnetospheric radio emission from confirmed exoplanets. Predicted radio fluxes from cataloged exoplanets are compared against the wavelengths and sensitivities of current and future observatories. Candidate exoplanets are downselected based on the sky coverage of each ground-based observatory. Orbits of target exoplanets are modeled to account for influential orbit-dependent effects in anticipating time-varying exoplanet radio luminosity and flux. To evaluate the angular alignment of exoplanetary beamed emission relative to Earth’s position, the equatorial latitude of exoplanetary auroral emission is compared against Earth’s apparent latitude on the exoplanet. Predicted time-dependent measurements and recommended beamformed observations for ground-based radio arrays are provided, along with a detailed analysis of the anticipated emission behavior for τ Boo b.

Observations of exoplanets open a new area of scientific activity and the structure of exoplanet magnetospheres is an important part of this area. Here we use symmetry arguments and experiences in spherical dynamo modeling to obtain the set of possible magnetic configurations for exoplanets and their corresponding host stars. The main part of our results is that the possible choice is much richer than the basic dipole magnetic field of both exoplanets and stars. Other options, for example, are quadrupole configurations or mixed parity solutions. Expected configurations of current sheets for the above mentioned exoplanet host star systems are presented as well.

AbstractUp to now, many techniques have been developed to detect and observe exoplanets, the radial velocity (RV) method being the most prolific one. However, stellar magnetic spots can mimic an exoplanet transit signal and lead to a false detection. A few models have already been developed to constrain the different signature of exoplanets and spots, but they only concern RV measurements or photometry. An interferometric approach, with high angular resolution capabilities, could resolve this problem.Optical interferometry is a powerful method to measure accurate stellar diameters, and derive fundamental parameters of stars and exoplanets minimum masses. We have built an analytical code able to calculate visibility moduli and closure phases of stars with a transiting exoplanet, to be compared with a star with no exoplanet. From the difference of interferometric signal, we can derive the presence of the exoplanet, but this requires that the star is resolved enough. We have tested this code with current available facilities like VEGA/CHARA and determined which already discovered exoplanets systems can be resolved enough to test this method.To make a more general study, we also tested different parameters (exoplanet and stellar diameters, exoplanet position) that can lead to a variation of the minimum baseline length required to see the exoplanet signal on the visibility modulus and the phase. Stellar spots act in the same way, but the difference of local intensity between an exoplanet transit and a spot can easily be studied thanks to the interferometric measurements.

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.

The non-thermal atmospheric losses due to the contribution of the exothermic photochemistry to the formation of a fractionof suprathermal atomic hydrogen in the H 2 → H transition region were studied and compared for two exoplanets of differenttypes and different parent star. Exoplanet GJ 436b is a warm neptune orbiting the red dwarf GJ 436. The calculated non-thermal fluxes due to the exothermic photochemistry for both exoplanets were found in the range (3.0 − 3.5) × 10 12 cm −2s −1 for a moderate level of stellar activity in UV radiation.

The values of the probability of a collision of a planetesimal with the Earth were typically greater for smaller distances Rfrom the Sun at 3 < R < 40 AU. The probability varied from about 10 −6 at R ∼ 30 − 40 AU to 10 −3 − 10 −2 at R about3.2-3.3 AU. Though only one of several hundreds of planetesimals from the zone of exoplanet c in the Proxima Centaurisystem reached the inner exoplanet b, it often collides with the planet b. The probability of a collision of such planetesimalwith the exoplanet b could be about several 10 −4 . A lot of icy material could be delivered to inner exoplanets b and d inthe Proxima Centauri system.

In March of 2022, NASA announced the discovery of the 5000th planet orbiting a star other than our sun (an exoplanet). We have created a sonification and visualization to celebrate this milestone and to communicate the exciting history of discovery to the general public. Our work provides a visceral experience of how humanity’s knowledge of alien worlds has progressed. A relatively simple and straightforward sonification mapping is used to make the informational content as accessible to the general public as possible. Listeners can see and hear the timing, number, and relative orbital periods of the exoplanets that have been discovered to date. The sonification was experienced millions of times through NASA’s social media channels and there are plans to update the sonification as future milestones are reached.

"Doppler boosting / de-boosting" is a well-known relativistic effect that alters the apparent luminosity of approaching/receding radiation sources. "Doppler boosting" alters the apparent luminosity of approaching light sources to appear brighter, while "Doppler de-boosting" alters the apparent luminosity of receding light sources to appear fainter. While "Doppler boosting / de-boosting" has been successfully accounted for and observed in relativistic jets of AGN, double white dwarfs, in search of exoplanets and stars in binary systems it was ignored in the establishment of Standard Candles for cosmological distances. A Standard Candle adjustment appears necessary for "Doppler de-boosting" for high Z, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of "Doppler de-boosting" but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)^(α-3) and for Type Ia supernova as ℳ(Z) = L/Lo=(Z+1)^(-2). These formulas are obtained within the framework of Special Relativity and may require adjustments within the General Relativity framework.