Dissertations / Theses on the topic 'Mass photometry'
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1
Steele, Iain A. "Photometry and spectroscopy of low mass stars and brown dwarfs." Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/35798.
Abstract:
This thesis describes an investigation of the faintest known proper motion members of the Pleiades star cluster. The primary aim of the work is an attempt to determine whether the lowest mass members of the cluster are brown dwarfs. A brief introduction outlines the fundamental properties of brown dwarfs and discusses the relation of research in this area to other branches of astronomy. The second chapter describes the basic principles of astronomical photometry and spectroscopy, the instruments used and the methods of data reduction. Chapter three gives a review of the current theory and observations of brown dwarfs. The results are presented in chapters four, five and six. RIJHK photometry for a sample of 62 objects is presented. The 1,1 - K diagram is shown to be a good discriminant of binary status for low mass cluster objects and using this diagram two single brown dwarf candidates and seven potential brown dwarf containing binaries are identified. FOS optical spectroscopy of 31 objects is used in an investigation of temperature indicators for cool stars. In addition gravity sensitive features indicate that the surface gravity of the Pleiades objects is lower than equivalent main sequence objects. Also discussed are the chromospheric and coronal activity of cluster members, and evidence is presented showing a turnover in both at ~ 0.3M⊕, where the objects become fully convective. CGS4 1-2.5 micron spectra are used in a futher investigation of methods of determining effective temperature and in searching for evidence of low mass companions. One object shows evidence for a low mass companion of ~ 0.035M⊕. Chapter seven discusses the evidence from these results that the faintest members observed are brown dwarfs and evidence from other workers that they are not. This chapter also gives suggestions for future work. Appendices compile the theoretical models and data used in the project.
2
Scandariato, Gaetano. "The Initial Mass Function of the Orion Nebula Cluster from Near-Infrared Photometry." Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/1027.
Abstract:
The main goal of this thesis is the complete characterization of the IMF of the Orion Nebula Cluster (ONC) down to the Brown Dwarfs (BDs) regime, using ground-based Near-Infrared (NIR) photometric observations. The data taken in the framework of the Hubble Space Telescope (HST) Treasury Program on the ONC have been obtained with the wide-field imager Infrared Side Port Imager (ISPI) at the Blanco 4m telescope of CTIO, and cover an area of about 0.25 square degrees roughly centered on Theta1OriC. We observed the region in the JHKS bands with exposure times of 330 s. As a result of our survey, we provide
2MASS-calibrated astrometry and photometry for ~7000 sources in the ONC region.
Analyzing our photometric sample, we derive the contamination-completeness corrected (J,J-H) CMDs of the ONC, canceling out the contribution from the contaminant population. We also develop a statistical algorithm, which combines the CMD of the ONC with our reference isochrone and, taking into account the presence of extinction and NIR excess, derives the intrinsic Luminosity Function (LF) of the cluster. We finally combine the LF with our empirical NIR isochrone to derive a statistical estimate of the IMF at different distances from the cluster center. We find that the mass distribution of the cluster is peaked at ~0.16 M and falls off crossing the hydrogen burning limit, continuously decreasing in the BDs domain down to ~0.03 M . We also find that the substellar-to-stellar objects ratio in the ONC decreases with increasing distance from the cluster center, suggesting that BDs are preferentially formed in the deep gravitational potential well where the most massive stars of the Trapezium cluster are also found.
3
Vika, Marina. "Supermassive black holes : the local supermassive black hole mass function." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2553.
Abstract:
Over recent years there has been an increase of the number of secure supermassive black hole (SMBH) detections. These SMBH measurements have lead astronomers to establish well defined empirical relationships between the SMBH mass and some of the properties of the host galaxy. The number of galaxies with SMBH mass measurements is currently limited to about 100. One approach of expanding the study of the SMBH is to use the empirical relations for estimating M[subscript(bh)] for larger samples of galaxies. The investigation of the SMBH population (or SMBH mass function) for large sample of galaxies in the nearby universe has helped to constrain the SMBH and the galaxy evolution. Previous estimates of the SMBH mass function at low redshift were produced mainly by combining the measurements of the galaxy luminosity or velocity function with one of the SMBH scaling relations. In the first part of the thesis I will present an independent construction of the nearby supermassive black hole mass function by applying the optical M[subscript(bh)]–L relation onto the Millennium Galaxy Catalogue (MGC). Additionally, in the second part I will provide photometric analysis of all UKIDSS galaxies for which SMBH masses have been measured. I will derive composite profiles of brightness, ellipticity and position angles of each galaxy. I will show that the Sérsic function fits the brightness profile of the majority of the elliptical galaxies and the bulge of disk galaxies and I will provide alternative multi-component fits when necessary. Then these photometric parameters will be used for constructing the M[subscript(bh)]–L relation in the near-IR and to investigate the M[subscript(bh)]–n relation. In the third part I will construct the near-IR SMBH mass function for the Galaxy and Mass Assembly (GAMA) survey. For this purpose I will apply the newly derived M[subscript(bh)]–L relation onto an elliptical subsample of K-band images. The advantage of this SMBH mass function is that during the M[subscript(bh)]–L construction I used the same quality images and techniques used on the GAMA survey. Apart from the M[subscript(bh)]–L relation, the M[subscript(bh)]–sigma relation was used as an alternative approach for a subsample of galaxies for which the velocity dispersions were available. Furthermore, I employed both local SMBH mass functions (MGC & GAMA) for estimating the SMBH mass density at redshift zero and accounted for the dependence of the total SMBH density on the look-back time by comparing with semi-analytic SMBH mass functions. Finally, from the SMBH mass density I estimated the baryon fraction that is locked into SMBHs.
4
Krawchuk, Curtis A. P. "The determination of metallicity and temperature of low-mass stars using broad-band photometry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0035/MQ27361.pdf.
5
King, Robert R. "Low-mass stars and brown dwarfs : optical/infrared photometry and spectroscopy of low-mass stars and brown dwarfs in the Field and Young Clusters." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/97095.
Abstract:
In this thesis I will present optical and near-infrared photometric and spectroscopic observations of an evolved field brown dwarf binary pair and of populations of low-mass stars in high-mass young stellar clusters and will compare them to stellar and substellar theoretical model predictions. Epsilon Indi Ba and Bb are the closest known brown dwarfs to the Earth, and, as such, make possible a concerted observational campaign to obtain a complete characterisation of two intermediate-age T dwarfs. Although some recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, there have been few conclusive tests to date. I will present high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R~5000) spectroscopy of these two T dwarfs. Using these data I have derived luminosities of log L/Lsun = -4.699 +/- 0.017 and -5.232 +/- 0.020 for Epsilon Indi Ba, Bb, respectively, and I will show that the predictions of substellar evolutionary models using luminosity and mass constraints are inconsistent with the effective temperatures and surface gravities derived from fitting atmospheric models to observed spectra. Furthermore, I will show that, even where estimates of the effective temperature, surface gravity, and luminosity are available, estimates of the mass of cool brown dwarfs can be up to a factor of two lower than the measured dynamical mass. Considering the difficulty in assigning accurate ages to any system and the mass-luminosity-age degeneracy of brown dwarfs, I would caution against the over-analysis of predicted brown dwarf masses at this time. I have also used Chandra X-ray observations to identify near-complete and relatively unbiased samples of pre-main-sequence stars in the young stellar clusters NGC 2244 and Trumpler 14. Using optical photometric and spectroscopic observations, I will characterise the apparent age spreads seen in the cluster pre-main-sequences. Mass estimates will then be derived for their stellar populations and used to construct the initial mass function for each cluster. It is found that NGC 2244 appears to have a Salpeter-like IMF for stars in the mass range 0.5--2.0 Msun if a likely age of 2 Myr is adopted, while Tr 14 may have a top-heavy IMF at a similar age. However, I will show that because the observed slopes of the cluster pre-main-sequences are not well-matched by the predicted slope in colour-magnitude space, such determinations are heavily dependent on the assumed age of the cluster and complicated due to the large spreads in isochronal ages.
6
Palmese, A., O. Lahav, M. Banerji, D. Gruen, S. Jouvel, P. Melchior, J. Aleksić, et al. "Comparing Dark Energy Survey and HST–CLASH observations of the galaxy cluster RXC J2248.7−4431: implications for stellar mass versus dark matter." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/622739.
Abstract:
We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (five filters) with those from the Hubble Space Telescope Cluster Lensing And Supernova Survey (CLASH; 17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25 per cent of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysis of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f(star) = (6.8 +/- 1.7) x 10(-3) within a radius of r(200c) similar or equal to 2 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both data sets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the similar to 100 000 clusters that will be observed within this survey and yield important information about galaxy evolution.
7
Garcia, E. Victor, Thayne Currie, Olivier Guyon, Keivan G. Stassun, Nemanja Jovanovic, Julien Lozi, Tomoyuki Kudo, et al. "SCExAO AND GPI Y JH BAND PHOTOMETRY AND INTEGRAL FIELD SPECTROSCOPY OF THE YOUNG BROWN DWARF COMPANION TO HD 1160." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623097.
Abstract:
We present high signal-to-noise ratio, precise Y JH photometry and Y band (0.957-1.120 mu m) spectroscopy of HD 1160 B, a young substellar companion discovered from the Gemini NICI Planet Finding Campaign using the Subaru Coronagraphic Extreme Adaptive Optics instrument and the Gemini Planet Imager. HD 1160 B has typical mid-M dwarf-like infrared colors and a spectral type of M5.5(-0.5)(+1.0), where the blue edge of our Y band spectrum rules out earlier spectral types. Atmospheric modeling suggests HD 1160 B has an effective temperature of 3000-3100 K, a surface gravity of log g - 4-4.5, a radius of. 1.55 +/- 0.10 R-J, and a luminosity of log L/L circle dot - 2.76 +/- 0.05. Neither the primary's Hertzspring-Russell diagram position nor atmospheric modeling of HD 1160 B show evidence for a subsolar metallicity. Interpretation of the HD 1160 B spectroscopy depends on which stellar system components are used to estimate the age. Considering HD 1160 A, B and C jointly, we derive an age of 80-125 Myr, implying that HD 1160 B straddles the hydrogen-burning limit (70-90 M-J) If we consider HD 1160 A alone, younger ages (20-125 Myr) and a brown dwarf-like mass (35-90 M-J) are possible. Interferometric measurements of the primary, a precise Gaia parallax, and moderate-resolution spectroscopy can better constrain the system's age and how HD 1160 B fits within the context of (sub) stellar evolution.
8
Pagotto, Ilaria. "Mass determination of supermassive black holes in nearby galaxies." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3427292.
Abstract:
This thesis focusses on the measure of the mass of supermassive black holes (SBH) lurking in the center of nearby quiescent galaxies. Increasing the demography of SBHs allows to study the correlations between their mass and the properties of their host to get insights about the joint evolution of SBHs and galaxies. New stringent limits on the SBH mass of 7 nearby galaxies are obtained by modeling the central width of the nebular emission lines measured over subarcsecond apertures with the Hubble Space Telescope (HST). The central stellar velocity dispersion of each galaxy is derived from new long-slit spectra from ground-based observations and the bulge effective radius is derived from a two-dimensional photometric decomposition of the i-band images from the Sloan Digital Sky Survey. The SBH-mass limits run parallel and above the relation between the SBH mass and the stellar velocity dispersion with no systematic trend depending on the galaxy distance or morphology. This gives further support to previous findings suggesting that the nuclear gravitational potential is remarkably well traced by the nebular-line width when the gas is centrally peaked. With this investigation, the number of galaxies with SBH-mass stringent limits obtained from nebular-line width increases to 114. These galaxies are further analyzed to more tightly constrain their SBH mass by taking into account the stellar mass contribution in the galaxy nucleus. To this aim the surface brightness distribution is measured from HST images and the mass-to-light ratio of an old and metal-rich stellar population is adopted for 100 nearby galaxies (D<103 Mpc) spanning a wide range of Hubble types (E-Sc) and central velocity dispersions (58-419 km/s). The shape of the profile of the emission lines and of the radial profile of emission-line flux are analysed to verify that nongravitational forces have a minor impact on the SBH-mass estimate. On average the stellar mass contribution is larger for galaxies with low effective velocity dispersion partly due to the presence of a nuclear stellar cluster or disk. Moreover, the stellar mass contribution is negligible in ellipticals and depends on the aperture size rather than on galaxy distance. These new SBH-mass limits run parallel to the relation between the SBH mass and the stellar velocity dispersion and they exceed the expected values by a median factor of 1.7. This is a striking result, since the dynamical analysis does not rely on spatially-resolved gas distribution and kinematics. Finally, new stellar velocity dispersions within subarcsecond apertures are obtained for the nuclei of a sample of 28 nearby galaxies. HST spectra obtained with the G750M grating are fitted using a library of single stellar population models and Gaussian emission lines, while constraining in most cases the stellar population content from an initial fit to HST G430L spectra. These measurements are useful for constraining the SBH mass as illustrated by the cases of the lenticular galaxies NGC 4435 and NGC 4459. These are characterized by similar ground-based stellar velocity dispersions but remarkably different SBH masses, where in particular NGC 4435 appears to host a significantly undermassive SBH compared to what expected from the relation between the SBH mass and stellar velocity dispersion. Jeans axisymmetric dynamical models are built to match the ground-based stellar kinematics obtained with integral-field spectroscopy assuming a SBH mass as predicted from the relation with the velocity dispersion and using high-resolution images as a base for constructing the stellar-mass model. Such reference models are used to make a prediction for the nuclear velocity dispersion. Whereas it agrees with the nuclear measurement for NGC 4459, for NGC 4435 the observed velocity dispersion is remarkably smaller than the predicted one, which further suggests that this galaxy hosts an undermassive SBH.Questo lavoro di tesi è dedicato alla misura della massa dei buchi neri supermassicci (SBH) che si celano al centro delle galassie quiescenti vicine. Aumentare il campione di SBH di massa nota permette di studiarne le relazioni con le altre proprietà delle galassie per poterne investigare l'evoluzione congiunta. Nuovi limiti stringenti sulla massa del SBH di 7 galassie sono stati fissati dalla misura della larghezza delle righe nebulari del gas ionizzato in spettri presi con l'Hubble Space Telescope (HST) entro aperture di dimensioni inferiori al secondo d'arco. La dispersione di velocità delle stelle è stata misurata con spettri a fenditura lunga presi da terra e il raggio efficace è stato ricavato dalla decomposizione fotometrica di immagini della Sloan Digital Sky Survey. Questi limiti di massa si dispongono parallelamente e al di sopra della relazione tra la massa del SBH e la dispersione di velocità delle stelle e non dipendono dalla morfologia o dalla distanza delle galassie. Questo suggerisce che il potenziale gravitazionale nei nuclei galattici è ben tracciato dalla larghezza delle righe di emissione se il gas si concentra verso il centro. Il numero delle galassie con un limite sulla massa del SBH ricavato dalla larghezza delle righe di emissione sale così a 114 oggetti. Queste galassie sono state ulteriormente analizzate includendo nel modello dinamico il contributo della massa stellare per ottenere limiti ancora più stringenti sulla massa del SBH. A tale scopo la brillanza superficiale misurata da immagini HST e il rapporto massa-luminosità tipico di una popolazione stellare vecchia e ricca in metalli sono stati usati per 100 galassie vicine (D<100 Mpc) e con un'ampia varietà di morfologie (E-Sc) e dispersioni di velocità (58-419 km/s). La forma dei profili delle righe di emissione e dell'andamento radiale del loro flusso sono stati studiati per escludere che le forze non gravitazionali giocassero un ruolo rilevante nella stima della massa del SBH. Il contributo stellare è maggiore per galassie con bassa dispersione di velocità, anche per la presenza di un ammasso/disco stellare nucleare, e trascurabile per le ellittiche. Esso dipende dalle dimensioni dell'apertura ma non dalla distanza della galassia. I nuovi limiti di massa si dispongono parallelamente alla relazione tra la massa del SBH e la dispersione di velocità ed eccedono il valore predetto dalla medesima solo di un fattore 1.7. Questo è un risultato notevole visto che il modello dinamico si basa su una distribuzione e cinematica del gas non spazialmente risolte. Infine, sono state ottenute nuove misure di dispersione di velocità stellare nel nucleo di 28 galassie. Gli spettri HST ottenuti con il reticolo G750M sono stati interpolati con modelli di popolazioni stellari e varie righe di emissione gaussiane, vincolando la popolazione stellare nel nucleo delle galassie grazie a spettri presi con il reticolo G430L. Queste misure permettono di porre dei forti vincoli sulla massa del SBH come mostrano i casi di NGC 4435 e NGC 4459. Si tratta di due galassie lenticolari caratterizzate da valori simili di dispersione di velocità stellare ma con masse di SBH molto diverse. In particolare, quella di NGC 4435 è molto più bassa rispetto a quanto predetto dalla relazione tra la massa del SBH e la dispersione di velocità stellare. Grazie a modelli dinamici stellari assisimmetrici è stata riprodotta la cinematica ottenuta da spettroscopia a campo integrale usando immagini HST e adottando come massa del SBH quella predetta dalla relazione con la dispersione di velocità. Questi modelli permettono di predire il valore centrale di dispersione di velocità e di confrontarlo con il valore osservato. Mentre per NGC 4459 il valore teorico e quello osservato sono in accordo, il valore misurato per NGC 4435 è molto più basso rispetto che a quello del modello dinamico indicando che la galassia ospita un SBH meno massiccio del normale.
9
Randriamampandry, Solohery Mampionona. "Stellar masses of star forming galaxies in clusters." University of the Western Cape, 2010. http://hdl.handle.net/11394/3028.
Abstract:
Magister Scientiae - MScWe determine the stellar mass of star forming galaxies in the X-ray luminous cluster MS 0451.6-0305 at z ∼ 0.54. The stellar masses are estimated from fitting model spectral energy distributions (SEDs) to deep, optical UBRIz observations obtained from WIYN 3.5m telescope and public NIR K-band image from Palomar Observatory telescope. The model SEDs are based on the stellar population synthesis (SPS) model of Bruzual & Charlot (2003) and Conroy et al. (2009) that span a wide range of age, star formation history, Initial Mass Function (IMF), metallicity and dust content. We measure stellar masses for galaxies down to M∗∼2×10⁸M(.) We find a tight correlation between stellar masses derived from the two SPSs. We compare the derived stellar masses to the dynamical masses for a set of 25 star forming galaxies. The dynamical masses are derived from high resolution, spectroscopic observations of emission lines from the DEIMOS spectrograph on the Keck telescope. A strong correlation is seen between the dynamical and stellar mass for the galaxies; and the star forming galaxies show fairly constant ratio between stellar and dynamical mass. When comparing to the field sample of Guzm ́an et al. (2003) of luminous compact blue galaxies, we see an excess of low mass galaxies in the cluster.
South Africa
10
Czanik, Robert Johann. "An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik." Thesis, North-West University, 2013. http://hdl.handle.net/10394/9102.
Abstract:
This study consisted of an optical photometric and spectroscopic analysis on a 7′ 7′ field around
the Southern high mass star forming region RCW 34. A previous study on RCW 34 in the NIR discov-
ered many deeply embedded young stellar objects which were suspected to be T Tauri stars and which
justified further investigation. The data used in this study consisted of three sets, the first two are
photometric and spectroscopic data sets which were obtained during the first two weeks of February
2002. A third data set of spectroscopic observations was obtained by the author during the second week
of 2011 of selected candidates using results from the NIR study and from the photometric data sets.
All of the spectroscopy was conducted with the long slit spectrograph on the 1.9-m telescope and the
photometry with DANDICAM on the 1.0-m telescope at the South African Astronomical Observatory
(SAAO) in Sutherland. Objectives accomplished in the course of this study were to understand, ob-
tain, reduce and interpret photometric and long slit spectroscopic CCD images. From the photometric
results 57 stars showed excess blue emission on a colour-colour diagram which could be generated by
circumstellar matter. The spectroscopic study showed 5 stars that showed H emission and 2 with
strong Li absorption lines which confirm the suspicions of the NIR study about T Tauri stars in the
region. All of the stars from the spectroscopic study in 2011 were identified as low-mass K or M type
stars. Using colour-magnitude diagrams it was possible to see that the majority of the stars in the
cluster are low-mass pre-main sequence stars. The stars matching between the optical and NIR filters
were plotted on NIR colour-colour diagrams showing that the 5 stars that had H emission lines also
had NIR colours characteristic to T Tauri stars. Out of the 5 stars that showed H emission, 2 were
found to be classical T Tauris and three were found to be weak line T Tauris.Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013
11
Burke, Christopher J. "Survey for transiting extrasolar planets in stellar systems stellar and planetary content of the Open Cluster NGC 1245 /." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1132168623.
12
Pastorelli, Giada. "Calibrating the thermally-pulsing asymptotic giant branch phase through resolved stellar populations in nearby galaxies." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3427185.
Abstract:
Most of the physical processes driving the Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) evolution are not yet fully understood and they need to be modelled with parametrised descriptions. The uncertainties of the models affect the interpretation of the spectrophotometric properties of galaxies up to high-redshift. In the framework of the ERC - STARKEY project, the aim of this Thesis is to constrain the uncertain parameters, i.e. third dredge-up and mass-loss, that still affect the TP-AGB models. To this purpose, I perform detailed simulations of AGB star populations in the Small Magellanic Cloud (SMC) based on robust measurements of the space-resolved star formation history as derived from the deep near-infrared photometry of the VISTA survey of the Magellanic Clouds. I compare the resulting synthetic catalogues with high-quality observations of resolved stellar populations in the infrared passbands of 2MASS and Spitzer. A large grid of TP-AGB evolutionary tracks is computed with several combinations of third dredge-up and mass-loss prescriptions. By requiring the models to reproduce the star counts and the luminosity functions of the observed Oxygen-, Carbon-rich and extreme-AGB stars, I put quantitative constraints on the efficiencies of the third dredge-up and mass-loss. The observed luminosity functions in all the available infrared photometric filters are successfully reproduced by two set of models, one with a relatively high mass-loss efficiency for Oxygen-rich stars and the second with a lower mass-loss efficiency and a lower efficiency of the third dredge-up for the more massive TP-AGB stars, i.e. initial masses larger than three solar masses. On the basis of the best-fitting model I present a complete characterisation of the AGB population in terms of stellar parameters, including the predicted mass-loss rates, initial masses, and Carbon-to-Oxygen ratio. I use the TP-AGB models calibrated in the SMC to model the population of Long Period Variables (LPVs) in the Large Magellanic Cloud as observed by Gaia. The remarkable agreement between models and observations allows us to guide the interpretation of a new observational diagram that is able to photometrically distinguish the evolutionary stages, the initial masses and the chemical type of these stars. In the context of the Large Synoptic Survey Telescope (LSST) science collaboration, I produce catalogues containing the synthetic photometry of the Magellanic Clouds in the Gaia and LSST filters. These catalogues, together with the all-sky simulations of the Milky Way will be made available to the community through the NOAO Data Lab to help defining the observing strategy of the LSST mini-surveys. In addition, I simulate samples of AGB stars in Local Group dwarf galaxies and find a general agreement with the data. However, to properly consider these objects in the TP-AGB models calibration, the simulations should be improved to take into account the crowding effects and the different areas used for the star formation histories derivation and the AGB stars identification. Finally, the products of this work, namely calibrated stellar isochrones and pulsation periods of LPVs, will be publicly available and ready to use for the interpretation of the data coming from present and future observing facilities. The calibrated TP-AGB models may be included in population synthesis models used to probe the integrated light of galaxies in the extragalactic Universe.La maggior parte dei processi fisici che controllano l'evoluzione delle stelle di ramo asintotico nella fase dei pulsi termici (TP-AGB) non sono ancora stati pienamente compresi e devono essere modellati con descrizioni parametriche. Le incertezze dei modelli hanno un impatto sull'interpretazione delle proprietà spettrofotometriche delle galassie fino ad alto redshift. Nel contesto del progetto ERC - STARKEY, lo scopo di questa Tesi è di vincolare i parametri incerti, ovvero il terzo dredge-up e la perdita di massa nei modelli stellari AGB. A tal fine, ho effettuato dettagliate simulazioni di popolazioni stellari della Piccola Nube di Magellano basate su robuste misure della storia di formazione stellare spazialmente risolta, derivata dalla fotometria infrarossa della survey VISTA delle Nubi di Magellano. Ho confrontato i risultati dei cataloghi sintetici con accurate osservazioni delle popolazioni stellari risolte nelle bande infrarosse di 2MASS e Spitzer. Un'estesa griglia di tracce evolutive TP-AGB è stata calcolata con diverse prescrizioni di perdita di massa e terzo dredge-up. Imponendo ai modelli di riprodurre i conteggi stellari e le funzioni di luminosità osservate delle stelle AGB e delle sottoclassi di AGB ricche di ossigeno, ricche di carbonio e delle stelle più arrossate, ho posto vincoli quantitativi sull'efficienza del terzo dredge-up e della perdita di massa. Le funzioni di luminosità osservate in tutti i filtri infrarossi disponibili sono riprodotte con successo da due set di modelli: il primo ha una perdita di massa con efficienza relativamente alta per le stelle ricche di ossigeno e il secondo ha un'efficienza di perdita di massa inferiore e una ridotta efficienza del terzo dredge-up per le stelle TP-AGB più massicce, ovvero con massa iniziale maggiore di circa tre masse solari. Sulla base di quest'ultimo set di modelli ho presentato una completa caratterizzazione della popolazione AGB della Piccola Nube di Magellano in termini di parametri stellari, inclusi i tassi di perdita di massa previsti, i valori di massa iniziale e rapporto carbonio ossigeno. Ho utilizzato i modelli TP-AGB calibrati nella Piccola Nube di Magellano per simulare le variabili a lungo periodo nella Grande Nube di Magellano osservate da Gaia. Il notevole accordo tra modelli e osservazioni ha permesso di guidare l'interpretazione di un nuovo diagramma osservativo capace di distinguere fotometricamente gli stadi evolutivi, le masse iniziali e il tipo chimico di queste stelle. Nel contesto della collaborazione scientifica Large Synoptic Survey Telescope (LSST), ho prodotto cataloghi contenenti la fotometria sintetica delle Nubi di Magellano nei filtri di Gaia e LSST. Questi cataloghi, assieme alle simulazioni della Galassia, saranno rese disponibili alla comunità scientifica tramite NOAO Data Lab per aiutare a definire la strategia osservativa dei programmi "mini-survey" di LSST. Inoltre, ho simulato alcuni campioni di stelle AGB in galassie locali e ho trovato un buon accordo tra dati e modelli. Tuttavia, per poter considerare questi oggetti nella calibrazione dei modelli TP-AGB è necessario migliorare le simulazioni per tenere conto degli effetti del crowding e delle diverse regioni utilizzate per la derivazione della storia di formazione stellare e l'identificazione delle stelle AGB. I prodotti di questo lavoro, ovvero isocrone stellari calibrate e periodi di pulsazione delle variabili a lungo periodo, saranno resi pubblicamente disponibili per interpretare dati osservativi già disponibili e dati che verranno rilasciati dai futuri telescopi. I modelli TP-AGB calibrati potranno essere inclusi in modelli di sintesi di popolazione utilizzati per analizzare la luce integrata di galassie nell'Universo extragalattico.
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Cariddi, Stefano. "The mass assembly in galaxies and clusters: a new perspective from the luminosity profiles." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3425239.
Abstract:
Context: Galaxy clusters are the largest virialized structures in the observable Universe. Knowledge of their properties provides many useful astrophysical and cosmological information.
Aim: Our aim is to derive the luminosity and stellar mass profiles of the nearby galaxy clusters of the Omega-WINGS survey, to study the main scaling relations valid for such systems and to compare them with those valid for early-type galaxies (ETGs).
Methods: We merged data from the WINGS and Omega-WINGS databases, sorted the sources according to the distance from the brightest cluster galaxy (BCG), and calculated the integrated luminosity profiles in the B and V bands, taking into account extinction, photometric and spatial completeness, K correction, and background contribution. Then, by exploiting the spectroscopic sample we derived the stellar mass profiles of the clusters.
Results: We obtained the luminosity profiles of 46 galaxy clusters, reaching the virial radius in 30 cases, and the stellar mass profiles of 42 of our objects. We successfully fitted all the integrated luminosity growth profiles with one or two embedded Sérsic components, deriving the main clusters parameters. We checked the main scaling relation among the clusters parameters in comparison with those obtained for a selected sample of ETGs of the same clusters.
Conclusions: We found that the nearby galaxy clusters are non-homologous structures such as ETGs and exhibit a color-magnitude (CM) red-sequence relation very similar to that observed for galaxies in clusters. These properties are not expected in the current cluster formation scenarios. In particular the existence of a CM relation for clusters, shown here for the first time, suggests that the baryonic structures grow and evolve in a similar way at all scales. We also provided an explanation of the properties of the fundamental plane relation of both clusters and ETGs in terms of a fine-tuning between the time-averaged star formation rate and the structural and dynamical characteristics of the system. Finally, we showed that the light profiles of clusters mirrors, in at least half cases, the light profile of the corresponding BCGs.Contesto: Gli ammassi di galassie sono le più grandi strutture virializzate dell’Universo osservabile e comprenderne le proprietà può fornire molte informazioni utili sia in ambito astrofisico che cosmologico. Scopo: Lo scopo del nostro lavoro è di derivare i profili di luminosità e massa per un campione di ammassi di galassie dell’Universo locale tratti dalla survey Omega-WINGS, di studiarne le principali relazioni di scala e di compararle con quelle valide per le galassie “early-type” (ETG). Metodo: Abbiamo unito i dati delle survey WINGS e Omega-WINGS, ordinato le sorgenti in funzione della loro distanza dalla galassia d’ammasso più brillante (BCG) e calcolato i profili di luminosità integrata nelle bande B e V, tenendo conto di estinzione, completezza spaziale e fotometrica, correzione K e sorgenti di campo. Infine, sfruttando il campione spettroscopico, abbiamo derivato i profili di massa stellare degli ammassi. Risultati: Abbiamo ottenuto i profili di luminosità di 46 ammassi di galassie, raggiungendo il raggio viriale in 30 casi, e i profili di massa di 42 di questi. Successivamente, abbiamo interpolato tutti i profili di luminosità con una o due componenti di Sérsic innestate l’una dentro l’altra, e abbiamo così derivato i parametri degli ammassi. Questi parametri sono stati usati per ottenere delle relazioni da paragonare a quelle valide per un campione di ETG degli ammassi stessi. Conclusioni: Abbiamo scoperto che gli ammassi di galassie analizzati sono strutture non omologhe (come le ETG) e che mostrano una sequenza di oggetti rossi nel diagramma colore-magnitudine (CM) molto simile a quella delle galassie d’ammasso. Queste proprietà non sono attese dal corrente scenario di formazione delle strutture cosmiche. In particolare, l’esistenza di una relazione CM per gli ammassi, identificata qua per la prima volta, suggerisce che le strutture di materia barionica crescano ed evolvano in maniera analoga a tutte le scale. Abbiamo inoltre fornito una spiegazione alle proprietà del piano fondamentale delle ETG e degli ammassi in termini di taratura fine tra il tasso di formazione stellare medio e le caratteristiche strutturali e dinamiche del sistema. Infine, abbiamo mostrato come in almeno metà dei casi il profilo di luminosità dell’ammasso rispecchi quello della rispettiva BCG.
14
Castel, Jérôme. "Developpements en spectrométrie de masse structurale pour la caratérisation de protéines d'intérêt thérapeutique." Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAF003.
Abstract:
Ce travail de thèse porte sur des développements méthodologiques en spectrométrie de masse (MS) structurale, principalement par échange hydrogène/deutérium couplé à la MS (HDX-MS), en MS native couplée ou non à la mobilité ionique (IM-MS) et plus récemment en photométrie de masse, pour la caractérisation de différentes protéines d’intérêt thérapeutique. Ce travail a notamment permis de montrer l’apport d’une combinaison d’approches en MS structurale pour la caractérisation approfondie des protéines membranaires, de l’analyse des protéines entières jusqu’à leur dynamique conformationnelle. La mise en place de nouvelles stratégies analytiques en IM-MS et en HDX-MS a également pu être évaluée pour la caractérisation structurale fine d’anticorps thérapeutiques. Enfin, l’intérêt de l’approche HDX-MS a été illustré pour le screening conformationnel et dynamique de ligands dans le cadre de l’étude d’interactions protéine/ligand impliquant des récepteurs nucléairesThis PhD work focuses on methodological developments in structural mass spectrometry (MS), especially by hydrogen/deuterium exchange coupled to MS (HDX-MS), by native MS coupled or not to ion mobility (IM-MS) and more recently mass photometry, for the characterization of various proteins of therapeutic interest. In particular, this work has demonstrated the contribution of a combination of structural MS approaches to the in-depth characterization of membrane proteins, from the analysis of intact proteins to their conformational dynamics. The implementation of new analytical strategies in IM-MS and HDX-MS has also been evaluated for the detailed structural characterization of therapeutic antibodies. Finally, the benefits of HDX-MS approach was illustrated for the conformational and dynamic screening of ligands in the context of the study of protein/ligand interactions involving nuclear receptors
15
McAllister, Martin J. "Photometric mass determinations of eclipsing cataclysmic variables." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19647/.
Abstract:
Cataclysmic variables (CVs) are a type of close, interacting binary system containing a white dwarf primary and a low-mass, Roche lobe-filling secondary/donor. Mass is commonly transferred from the donor to an accretion disc around the white dwarf, due to the conservation of angular momentum, before eventually reaching the surface of the white dwarf. A region of increased luminosity, termed the 'bright spot', exists at the intersection of accretion disc and mass transfer stream. The transfer of mass within the system is a turbulent process, giving rise to random photometric variations commonly referred to as 'flickering'. For high inclination systems, the donor eclipses all other components within the system, resulting in complex eclipse light curves that can be fit with a parameterised model to obtain system parameters. Eclipses of the white dwarf and bright spot occur in quick succession, and therefore precise eclipse modelling requires high-time-resolution photometry. Flickering is a hindrance to eclipse modelling, however, as it can obscure ingress/egress features of the component eclipses, and therefore existing studies use eclipse averaging to minimise its effects. In this thesis, a new approach to eclipse modelling is introduced, which involves modelling flickering through the utilisation of Gaussian processes (GPs). The new modelling approach is implemented on ULTRACAM/ULTRASPEC eclipse light curves of 18 eclipsing CVs, returning 18 sets of precise system parameters. Four of these systems have been modelled previously using the existing approach, while 14 are modelled for the first time. The 18 new/revised white dwarf and donor masses from this work are used alongside other CV component masses from the literature in an attempt to secure a better understanding of CVs and their evolution. One of the outcomes is a new estimate for the CV orbital period minimum, 79.57+-0.22 min, which is over 2 min shorter than previously thought.
16
Richardson, Matthew. "Mass Estimation through Fusion of Astrometric and Photometric Data Collection with Application to High Area-to-Mass Ratio Objects." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1742.
Abstract:
This thesis work presents the formulation for a tool developed in MATLAB to determine the mass of a space object from the fusion of astrometric and photometric data. The application for such a tool is to better model the mass estimation method used for high area-to-mass ratio objects found in high altitude orbit regimes. Typically, the effect of solar radiation pressure is examined with angles observations to deduce area-to-mass ratio calculations for space objects since the area-to-mass ratio can greatly affect its orbital dynamics. On the other hand, photometric data is not sensitive to mass but is a function of the albedo-area and the rotational dynamics of the space object. Thus from these two data types it is possible to disentangle intrinsic properties using albedo-area and area-to-mass and ultimately determine the mass of a space object. Three case studies were performed for the different orbit regimes: geosynchronous, highly elliptic, and medium earth orbit. The position states were either initialized with a two line element set or with initial orbit determination methods to simulate data which was run through an unscented Kalman filter to estimate the translational and rotational states of the space object as well as the mass an albedo area. In the geosynchronous and highly elliptic cases the tool was able to accurately predict the mass value to within 5kg of the true value based on a 95% confidence interval which will allow applications to understanding high area-to-mass objects with high certainty.
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Fernando, Jennifer. "Caractérisation des propriétés physiques de la surface de Mars à partir de mesures spectro-photométriques orbitales." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112293/document.
Abstract:
Depuis leur formation, les surfaces des corps de notre Système Solaire montrent une diversité étonnante. Cette diversité est le reflet des processus géologiques qui ont modelé les surfaces planétaires au cours du temps. Parmi les objets du Système Solaire, Mars constitue un objet particulièrement intéressant car il présente de nombreuses similitudes avec notre planète. La minéralogie de la surface de Mars est bien documentée. Cependant, on dispose de peu d'information sur les paramètres physiques des matériaux qui sont également des traceurs des processus géologiques. Un des objectifs de cette thèse est de développer et de valider un outil permettant leur détermination à partir de techniques d'investigation spatiale depuis l'orbite et d’interpréter les résultats. Pour cela, une approche basée sur la photométrie, qui étudie les propriétés de diffusion des matériaux de surface, a été développée et validée. Ces propriétés de diffusion dépendent de la composition mais aussi des propriétés physiques des matériaux comme la taille, la forme, la structure interne, la rugosité des grains et la rugosité de la surface. Les données hyperspectrales multi-angulaires CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) à bord de la sonde Mars Reconnaissance Orbiter (11 images prises à des angles d'émergence variés) ont été utilisées, permettant de contraindre le comportement de diffusion des matériaux de surface. Tout d'abord, les données sont corrigées de la contribution atmosphérique à l'aide de l'algorithme nommée MARS-ReCO (Multi-angle Approach for Retrieval of Surface Reflectance for CRISM Observations), développé en collaboration avec Xavier Ceamanos et Sylvain Douté (IPAG) au cours de la thèse. Puis, les données de réflectance de surface à différentes géométries sont analysées en inversant à l’aide d’une approche bayésienne le modèle photométrique de Hapke qui décrit le transfert radiatif en milieu granulaire. Ce modèle dépend de six paramètres photométriques de surface (e.g., albédo de diffusion, fonction de phase, rugosité macroscopique de la surface), reliés aux propriétés physiques des matériaux comme la taille, la structure interne, la forme, la rugosité des grains, et la rugosité de la surface.Une première application a été menée au niveau des sites d'atterrissage des rovers de la mission Mars Exploration Rover, où des données orbitales et in situ sont disponibles. Ces dernières sont utilisées comme «vérité terrain» pour valider les interprétations des paramètres photométriques estimés. Dans ce travail, des cartes des paramètres photométriques ont été fournies le long et autour du trajet des rovers permettant d'avoir accès aux informations des propriétés des matériaux sur une étendue plus importante que les données in situ. Une interprétation de chacun des paramètres et un lien aux propriétés physiques et aux processus géologiques ont été fournis. Les résultats montrent des propriétés de diffusion variés au sein d'une observation CRISM (10x10km) suggérant que les surfaces sont contrôlées par des processus géologiques plus locaux (e.g., processus éoliens, fragmentation de la croûte par impact).Une dernière partie se focalise sur la détermination des propriétés de diffusion des matériaux de surface de différents terrains géologiques formés dans des contextes différents. Le but est d'identifier les variabilités des propriétés de diffusion à travers MarsThe PhD work focuses on the characterization of geological processes on planetary surfaces. Due to the lack of broad scale in situ information about the surface physical properties of the Martian materials (recording the geological processes), my work centers on the development and validation of an approach for their estimation from orbital spaceborne datasets. In addition, determining the physical properties has an implication for the spectroscopic interpretation notably for the mineral abundances. More specifically, I developed an approach for the determination and the analysis of the Martian surface scattering properties using CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) observations [Murchie et al., 2007] on-board MRO (Mars Reconnaissance Orbiter). CRISM provides multi-angular (varied emission angles) hyperspectral images which allow the characterization of the surface scattering behavior at ∼200m/pixel. The scattering behavior depends on the material composition but also the physical properties such as the grain size, shape, internal structure, and the surface roughness / porosity. The main objective is to observe the spatial variations of the surface scattering properties and the photometric parameters as a function of geological units.The methodology I employ is based on the estimation of the surface photometric parameters in term of surface physical properties. After an atmospheric correction (aerosols) by the Multi-angle Approach for Retrieval of the Surface Reflectance from CRISM Observations (MARS-ReCO) [Ceamanos et al., 2013] developed in collaboration with X. Ceamanos and S. Douté (IPAG, France), I analyze the surface reflectance taken at varied geometries by inverting the Hapke photometric model [Hapke, 1993] depending on six parameters (single scattering albedo, 2-term phase function, macroscopic roughness and 2-term opposition effects parameters) in a Bayesian framework [Fernando et al., 2013]. The algorithm for the correction for the aerosols and the methodology for the estimates of surface photometric parameters have been validated by comparing the results from orbit to the in situ photometric measurements from Mars Exploration Rover (MER) rovers [Fernando et al. 2013].The MER landing sites located at Gusev Crater and Meridiani Planum provide an excellent opportunity to ground truth and validate the interpretation of derived Hapke photometric parameters as both orbital and in situ data are readily available over numerous geological terrains. Orbital results are consistent with the in situ observations. In my work, I mapped the surface scattering properties in and around the rover path, providing extended information over a wider area. Significant variations in the scattering properties are observed inside a CRISM observation (10x10km) suggesting that the surfaces are controlled by local geological and climatic processes [Fernando et al., in revision].The last part of this work focuses on the determination of the surface photometric parameters of different Martian geological terrains under different contexts in order to identify variabilities of the scattering properties
18
Perakis, Nikolaos. "Separation et detection selective des composes soufres dans les fractions lourdes des petroles : geochimie des benzo (b) thiophenes." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13093.
Abstract:
Analyse et dosage des composes soufres presents dans une coupe lourde du petrole aramco 90 par chromatographie gazeuse avec detection soit par photometrie de flamme soit par spectrometrie de masse haute resolution. Etude comparative des methodes d'analyse. Etude des composes soufres dans des echantillons de petrole de rozel point et de schiste bitumineux de timahdit grace a l'identification par synthese de nouvelles familles d'alkylbenzo (b) thiophenes
19
Karalidi, Theodora, Dániel Apai, Mark S. Marley, and Esther Buenzli. "MAPS OF EVOLVING CLOUD STRUCTURES IN LUHMAN 16AB FROM HST TIME-RESOLVED SPECTROSCOPY." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621380.
Abstract:
WISE J104915.57-531906.1 is the nearest brown dwarf binary to our solar system, consisting of two brown dwarfs in the L/T transition: Luhman 16A and B. In this paper, we present the first map of Luhman 16A, and maps of Luhman 16B for two epochs. Our maps were created by applying Aeolus, a Markov-Chain Monte Carlo code that maps the top-of-the-atmosphere (TOA) structure of brown dwarf and other ultracool atmospheres, to light curves of Luhman 16A and B using the Hubble Space Telescope's G141 and G102 grisms. Aeolus retrieved three or four spots in the TOA of Luhman 16A and B, with a surface coverage of 19%-32% (depending on an assumed rotational period of 5 hr or 8 hr) or 21%-38.5% (depending on the observational epoch), respectively. The brightness temperature of the spots of the best-fit models was similar to 200 K hotter than the background TOA. We compared our Luhman 16B map with the only previously published map. Interestingly, our map contained a large TOA spot that was cooler (Delta T similar to 51 K) than the background, which lay at low latitudes, in agreement with the previous Luhman 16B map. Finally, we report the detection of a feature reappearing in Luhman 16B light curves that are separated by tens of hundreds of rotations from each other. We speculate that this feature is related to TOA structures of Luhman 16B.
20
Miles-Paez, Paulo A., Stanimir A. Metchev, Aren Heinze, and Daniel Apai. "Weather on Other Worlds. IV. H alpha Emission and Photometric Variability Are Not Correlated in L0-T8 Dwarfs." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624337.
Abstract:
Recent photometric studies have revealed that surface spots that produce flux variations are present on virtually all L and T dwarfs. Their likely magnetic or dusty nature has been a much-debated problem, the resolution to which has been hindered by paucity of diagnostic multi-wavelength observations. To test for a correlation between magnetic activity and photometric variability, we searched for Ha emission among eight L3-T2 ultra-cool dwarfs with extensive previous photometric monitoring, some of which are known to be variable at 3.6 mu m or 4.5 mu m. We detected Ha only in the non-variable T2 dwarf 2MASS J12545393-0122474. The remaining seven objects do not show Ha emission, even though six of them are known to vary photometrically. Combining our results with those for 86 other L and T dwarfs from the literature show that the detection rate of Ha emission is very high (94%) for spectral types between L0 and L3.5 and much smaller (20%) for spectral types. >= L4, while the detection rate of photometric variability is approximately constant (30%-55%) from L0 to T8 dwarfs. We conclude that chromospheric activity, as evidenced by H alpha emission, and large-amplitude photometric variability are not correlated. Consequently, dust clouds are the dominant driver of the observed variability of ultra-cool dwarfs at spectral types, at least as early as L0.
21
Obermeier, Christian, Thomas Henning, Joshua E. Schlieder, Ian J. M. Crossfield, Erik A. Petigura, Andrew W. Howard, Evan Sinukoff, et al. "K2 DISCOVERS A BUSY BEE: AN UNUSUAL TRANSITING NEPTUNE FOUND IN THE BEEHIVE CLUSTER." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622698.
Abstract:
Open clusters have been the focus of several exoplanet surveys, but only a few planets have so far been discovered. The Kepler spacecraft revealed an abundance of small planets around small cool stars, therefore, such cluster members are prime targets for exoplanet transit searches. Kepler's new mission, K2, is targeting several open clusters and star-forming regions around the ecliptic to search for transiting planets around their low-mass constituents. Here, we report the discovery of the first transiting planet in the intermediate-age (800 Myr) Beehive cluster (Praesepe). K2-95 is a faint (Kp = 15.5 mag) M3.0 +/- 0.5 dwarf from K2's Campaign 5 with an effective temperature of 3471 +/- 124 K, approximately solar metallicity and a radius of 0.402 +/- 0.050 R-circle dot. We detected a transiting planet with a radius of 3.47(-0.53)(+0.78)R(circle plus) and an orbital period of 10.134 days. We combined photometry, medium/high-resolution spectroscopy, adaptive optics/speckle imaging, and archival survey images to rule out any false-positive detection scenarios, validate the planet, and further characterize the system. The planet's radius is very unusual as M-dwarf field stars rarely have Neptune-sized transiting planets. The comparatively large radius of K2-95b is consistent with the other recently discovered cluster planets K2-25b (Hyades) and K2-33b (Upper Scorpius), indicating systematic differences in their evolutionary states or formation. These discoveries from K2 provide a snapshot of planet formation and evolution in cluster environments and thus make excellent laboratories to test differences between field-star and cluster planet populations.
22
Martin, Christian. "Contribution a l'etude des etoiles doubles hipparcos. Photometrie des doubles visuelles et calcul de masse des binaires a courte periode." Nice, 1996. http://www.theses.fr/1996NICE4971.
Abstract:
De novembre 1989 a avril 1993, le satellite astrometrique hipparcos de l'agence spatiale europeenne a observe pres de 120 000 etoiles plus brillantes que 13 mag, dans le but de determiner leurs positions, parallaxes et mouvements propres avec une precision de l'ordre de la milliseconde d'arc, ainsi que leurs magnitudes dans une bande visible large. Parmi ces etoiles figurent environ 11 500 etoiles doubles connues comme telles au debut de la mission, population enrichie de 6000 binaires supplementaires decouvertes au cours du traitement des donnees. Ce traitement, confie de facon independante a deux consortiums scientifiques, fast et ndac, est aujourd'hui acheve. Ce travail concerne la reduction des donnees photometriques concernant l'ensemble des etoiles doubles, au sein du consortium fast, dont le but est de produire les differences de magnitude des composantes. Une simulation a permis de mettre en evidence d'importantes erreurs systematiques affectant l'estimation de cette difference, et de les quantifier afin de pouvoir les corriger. Dans toutes les phases du traitement, le recours a la robustesse statistique a ete necessaire pour ecraser l'influence d'observations aberrantes, et pour tenir compte du comportement non-gaussien des variables impliquees. La precision typique obtenue est de 0. 04 mag pour la difference de magnitude et de 0. 015 et 0. 04 mag respectivement pour les magnitudes de la primaire et de la secondaire. On demontre d'autre part la possibilite de determiner directement les masses des composantes de binaires orbitales dont la periode ne depasse pas trente ans, a partir des donnees hipparcos et de la connaissance des elements orbitaux. Une simulation montre que le rapport de masses est disponible lorsque la separation du couple depasse typiquement 0''. 3. Dans le cas contraire, on determine une combinaison entre celui-ci et la difference de magnitude. Les resultats sont presentes pour une cinquantaine de couples, parmi 150 testes. Le systeme triple algol a fait l'objet d'une etude particuliere fournissant aussi les magnitudes individuelles des trois composantes
23
Shan, Yutong, Jennifer C. Yee, Brendan P. Bowler, Lucas A. Cieza, Benjamin T. Montet, Héctor Cánovas, Michael C. Liu, et al. "The Multiplicity of M Dwarfs in Young Moving Groups." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627110.
Abstract:
We image 104 newly identified low-mass (mostly M-dwarf) pre-main sequence (PMS) members of nearby young moving groups (YMGs) with Magellan Adaptive Optics (MagAO) and identify 27 stellar binaries with instantaneous projected separation as small as 40 mas. Fifteen were previously unknown. The total number of multiple systems in this sample including spectroscopic and visual binaries from the literature is 36, giving a raw stellar multiplicity rate of at least 35(-4)(+5)% for this population. In the separation range of roughly 1-300 au in which infrared AO imaging is most sensitive, the raw multiplicity rate is at least 24(-4)(+5)% for binaries resolved by the MagAO infrared camera (Clio). The M-star subsample of 87 stars yields a raw multiplicity of at least 30(-4)(+5)% over all separations, 21(-4)(+5)% for secondary companions resolved by Clio from 1 to 300 au (23(-4)(+5)% for all known binaries in this separation range). A combined analysis with binaries discovered by the Search for Associations Containing Young stars shows that stellar multiplicity fraction as a function of mass over the range of 0.2 to 1.2M(circle dot) appears to be linearly flat, in contrast to the field, where multiplicity increases with mass. After bias corrections are applied, the multiplicity of low-mass YMG members (0.2-0.6M(circle dot)) is in excess of the field. The overall multiplicity fraction is also consistent with being constant in age and across YMGs, which suggests that multiplicity rates for this mass range are largely set by 10 Myr without appreciable evolution thereafter.
24
Lamareille, Fabrice. "Évolution cosmologique des propriétés physiques des galaxies." Phd thesis, Université Paul Sabatier - Toulouse III, 2006. http://tel.archives-ouvertes.fr/tel-00090655.
Abstract:
L'étude de la formation et de l'évolution des galaxies est une thématique en pleine effeversence. Deux grands relevés (2dFGRS, SDSS), portant sur plusieurs millions de galaxies proches, ont permis récemment des avancées importantes dans la compréhension des propriétés physiques des galaxies. D'autre part l'arrivée des télescopes de 8-10m de diamètre, équipés de spectroscopes multi-objets (VLT/VIMOS, Keick/DEIMOS, Gemini/GMOS, ...), a permis la mise en place de plusieurs nouveaux grands relevés portant cette fois sur les galaxies lointaines (VVDS, DEEP2, GDDS, zCOSMOS, ...), donc situées dans un univers plus jeune.Ce travail de thèse porte préférentiellement sur l'étude des relations masse-métallicité ou luminosité-métallicité qui permettent d'établir un lien entre les deux processus majeurs responsables de l'évolution des galaxies: l'assemblage de la masse stellaire (formation d'étoiles ou fusion de galaxies) et l'enrichissement chimique du milieu interstellaire par les générations d'étoiles successives. Nous montrons que la forme de cette relation est un très bon test des modèles de formation et d'évolution des galaxies. Nous étudions ensuite la relation luminosité-métallicité de référence obtenue à partir du relevé 2dFGRS dans l'Univers local. Puis nous étudions l'évolution en fonction de l'âge de l'univers de la relation luminosité-métallicité à l'aide d'un petit échantillon (LCL05), puis de la relation masse-métallicité à l'aide du grand relevé VVDS. Plusieurs résultats obtenus avec ces différents échantillons sont des indices en faveur du modèle hiérarchique: les galaxies les plus massives se formeraient par fusion progressive de galaxies plus petites.
Les propriétés physiques d'un grand nombre de galaxies sont estimées à l'aide d'outils d'analyse automatiques spécifiquement développés, ou adaptés à nos besoins, durant cette thèse. Comme résultats annexes, de nouvelles calibrations de la classification spectrale ou du taux de formation d'étoiles des galaxies sont obtenues à partir des grands relevés de l'univers local (respectivement 2dFGRS et SDSS). Ce travail offre de nombreuses perspectives de par le nombre et la diversité des données disponibles.
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Lyo, A.-Ran Physical Environmental & Mathematical Sciences Australian Defence Force Academy UNSW. "The nearby young [special character] Chamaeleontis cluster as a laboratory for star formation and evolution." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Physical, Environmental and Mathematical Sciences, 2004. http://handle.unsw.edu.au/1959.4/38707.
Abstract:
[Special characters cannot be displayed. Please see the pdf version of the Abstract for an accurate reproduction.] We studied the circumstellar discs, the initial mass function (IMF), mass distribution, binarity and the fundamental properties of the [special character] 9 Myr-old pre-main sequence (PMS) [special character] Chamaeleontis cluster. Using JHKL colour-colour and colour-excess diagrams, we found the circumstellar disc fraction to be [special character] 0.60 among the late-type members. Four stars with [special character] (K - L) > 0.4 were identified as experiencing ongoing accretion which was later confirmed by high-resolution spectroscopic study. Quantitative analysis of the H[special character] profiles found accretion in these four stars at rates comparable to that of two members of the similarly-aged TW Hydrae Association (TWA); rates 1 - 3 orders of magnitude lower than in younger classical T Tauri stars. Together these results suggest that, while the mass accretion rate decreases with age, PMS stars can retain their inner discs for [special character] 10 Myr. An optical photometric survey spanning 1.3 ?? 1.3 pc added two low-mass stars to the cluster inventory. Together with other recent surveys the population is likely to be significantly complete for primaries with masses M > 0.15M[special character]. The cluster now consists of 18 primaries and 9 confirmed and candidate secondaries, with [special character] 2-4 times higher multiplicity than seen in field dwarfs. The cluster IMF is consistent with that of rich young clusters and field stars. By extending the IMF to lower masses, we predict 20-29 low-mass stars and brown dwarfs may remain undiscovered. From study of the cluster???s spatial and mass distribution, we find the [special character] Cha cluster has significant mass segregation, with > 50 per cent of the stellar mass residing within the central 0.17 pc. Lastly we classified members of the cluster with low-resolution spectra, providing information about the fundamental properties of the PMS stars by comparison to standard dwarfs. Broadband VRI colours and pseudocontinuum indices derived for the cluster stars are indistinguishable from dwarfs at visual and red wavelengths. This suggests the temperature sequence for the PMS [special character] Cha cluster is similar to that of the dwarf sequence. Narrow-band spectral indices for the [special character] Cha cluster possibly indicate higher metallicity and strongly indicate lower surface gravity than the dwarf indices.
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Pablo, Herbert, Noel Richardson, Anthony Moffat, Michael Corcoran, Tomer Shenar, Omar Benvenuto, Jim Fuller, et al. "A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. III. Analysis of Optical Photometric (MOST) and Spectroscopic (Ground Based) Variations." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/6234.
Abstract:
We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system δ Ori A, consisting of a binary O9.5II+early-B(Aa1 and Aa2) with P=5.7 days, and a more distant tertiary(O9 IV P 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV)curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
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Cesetti, Mary. "Observational constraints to the stellar populations in the center of galactic spheroids." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426046.
Abstract:
Galactic spheroids represent one of the key challenges to our understanding of galaxies formation and evolution as far as their star-formation history is concerned. The knowledge of the stellar content of early-type galaxies is fundamental to understand their star formation and chemical evolution. The thesis is focused on two main topics, both concerned with the study of unresolved stellar populations in the centers of galaxies. The first one is a comprehensive study of the photometrical properties of three galaxies that belong to the Virgo Cluster and host Nuclear Stellar Disks (NSD) in their centers. The second one is focused on the study of absorption lines in the Near-infrared (NIR) that are strictly correlated with the properties of the stellar populations. I defined new NIR spectral indices that show great potential for a stellar population analysis. A simple SSP model is created to interpret the integrated NIR light. The development of the SSPs model pointed out at some limitations of the currently available stellar spectral libraries. Consequently, the study of metal poor red supergiant stars in the NIR was carried out.Gli sferoidi galattici rappresentano uno dei punti chiave per comprendere la formazione e l'evoluzione delle galassie, sopratutto per quanto riguarda la formazione stellare. Infatti, conoscere il contenuto stellare delle galassie early-type fornishe importanti indicazioni sulla formazione e l'evoluzione chimica delle loro stelle. Due sono gli argomenti trattati in questa tesi entrambi connessi con lo studio delle popolazione stellari non risolte nel centro delle galassie. Il primo studia dettagliatamente le proprietà fotometriche di tre galassie appartenenti all'ammasso della Vergine che ospitano un disco stellare nel loro nucleo. Il secondo mira ad individuare le righe spettrali fondamentali per lo studio delle popolazioni stellari nel vicino infrarosso (NIR). I nuovi indici spettrali definiti nel NIR hanno dimostrato essere notevolmente efficaci per l'analisi delle popolazioni stellari. Un semplice modello di popolazione stellare semplice (SSP) è stato creato per interpretare la luce integrata nel vicino infrarosso. Lo sviluppo del modello SSP ha messo in evidenza alcuni limiti delle librerie stellari spettrali oggigiorno disponibili. Pertanto è stato studiato lo spettro di alcune stelle supergiganti rosse a bassa metallicità nel NIR.
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Lindgren, Sara. "Metallicity determination of M dwarfs." Doctoral thesis, Uppsala universitet, Observationell astrofysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-332102.
Abstract:
M dwarfs constitute around 70% of all stars in the local Galaxy. Their multitude together with their long main-sequence lifetimes make them important for studies of global properties of the Galaxy such as the initial mass function or the structure and kinematics of stellar populations. In addition, the exoplanet community is showing an increasing interest for those small, cold stars. However, very few M dwarfs are well characterized, and in the case of exoplanetary systems the stellar parameters have a direct influence on the derived planet properties. Stellar parameters of M dwarfs are difficult to determine because of their low surface temperatures that result in an optical spectrum dominated by molecular lines. Most previous works have therefore relied on empirical calibrations. High-resolution spectrographs operating in the infrared, a wavelength region less affected by molecular lines, have recently opened up a new window for the investigation of M dwarfs. In the two first papers of this thesis we have shown that we can determine the metallicity, and in some cases the effective temperature, using synthetic spectral fitting with improved accuracy. This method is time consuming and therefore not practical or even feasible for studies of large samples of M dwarfs. When comparing our results from the high-resolution studies with available photometric calibrations we find systematic differences. In the third paper we therefore used our sample to determine a new photometric metallicity calibration. Compared to previous calibrations our new photometric calibration shows improved statistical characteristics, and our calibration gives similar results as spectroscopic calibrations. In a comparison with theoretical calculations we find a good agreement of the shapes and slopes of iso-metallicity lines with our empirical relation. Applying the photometric calibration to a sample of M dwarfs with confirmed exoplanets we find a possible giant planet-metallicity correlation for M dwarfs.
29
Delorme, Philippe. "Les naines brunes dans les relevés grand champ." Phd thesis, Grenoble 1, 2008. http://www.theses.fr/2008GRE10155.
Abstract:
Mon travail de recherche au cours de ces trois années de thèse sous la direction de Thierry Forveille et de Xavier Delfosse au laboratoire d'astrophysique de Grenoble a été consacré à la recherche de naines brunes dans un relevé grand champ de nouvelle génération que nous avons appelé le Canada-France Brown Dwarf Survey -CFBDS-. La thématique de ma thèse est centrée sur l'étude des naines brunes froides et la constitution d'un grand échantillon de naines brunes, comme base pour une analyse statistique photométrique et spectroscopique. Tétais chargé en premier lieu de la mise au point du pipeline d'analyse et de sélection des candidats au sein de la collaboration internationale dédiée à la recherche de naines brunes et de quasars à grand décalage vers le rouge. Dans le chapitre l, je fais un récapitulatif rapide de l'ensemble des avancées scientifiques dans le domaine des naines brunes avant la présente thèse. Le chapitre 2 présente le Canada- France Brown Dwarf Survey, qui fournit les données au coeur de mon travail, ainsi que notre stratégie d'analyse. Le chapitre 3 détaille le pipeline que j'ai mis en place pour identifier au mieux les naines brunes dans les images grand champs et présente une évaluation de ses performances. Les candidats ainsi identi és sur la base de leur photométrie sont présentés dans le chapitre 4. Dans ce chapitre je décris mes méthodes d'estimation des biais statistiques du CFBDS, ainsi que la fonction de luminosité des naines brunes du champ que nous en avons extraite. Enfin le chapitre 5 donne une revue des informations contenues dans le spectre des naines brunes. J'y présente ensuite les résultats issus de nos observations spectroscopiquesMy PhD research work, under the supervision of Thierry Forveille and Xavier Delfosse at the laboratoire d'astrophysique de Grenoble, is centered on identifying brown dwarfs in a new-generation wide-field survey, the Canada-France Brown Dwarfs Survey -CFBDS-. Its main goals are to identify cooler and low metallicity brown dwarfs for detailed study, and to assemble a large sample of more ordinary brown dwarfs for statistical analyses. My role, as the only full-time member of this international collaboration, included the programming of an analysis and selection pipeline to identify the rare brown dwarf candidates in the very large image database, as well as coordination of the internation collaboration. Chapter 1 summarizes the state of brown dwarf science at the start of this PhD. Chapter 2 presents the Canada-France Brown Dwarfs and our analysis strategy. Chapter 3 describes the pipeline 1 developed to optimally identify brown dwarfs (as well as high redshift quasars) candidates in the CFBDS images. This chapter also describes the Point Spread Function -PSF- fitting module which 1 added to the well known \textit{Source Extractor} image analysis package. Chapter 4 presents the resulting brown dwarf candidates, assesses the statistical biases of the CFBDS survey, and evaluates the associated field brown dwarfs luminosity function. Finally, Chapter 5 briefly reviews the the physical informations which can be extracted from brown dwarfs spectra, and examines in that light the spectra which we obtained for two dozen of our candidates. It ends with discussions of our disco very of the cooldest brown dwarf published to date, CFBDS0059, and of what is likely the first T subdwarf
30
Delorme, Philippe. "Les naines brunes dans les relevés grand champ." Phd thesis, Université Joseph Fourier (Grenoble), 2008. http://tel.archives-ouvertes.fr/tel-00351010.
Abstract:
Mon travail de recherche au cours de ces trois années de thèse sous la direction de Thierry Forveille et de Xavier Delfosse au laboratoire d'astrophysique de Grenoble a été consacré à la recherche de naines brunes dans un relevé grand champ de nouvelle génération que nous avons appelé le Canada-France Brown Dwarf Survey -CFBDS-. La thématique de ma thèse est centrée sur l'étude des naines brunes froides et la constitution d'un grand échantillon de naines brunes, comme base pour une analyse statistique photométrique et spectroscopique. J'étais chargé en premier lieu de la mise au point du pipeline d'analyse et de sélection des candidats au sein de la collaboration internationale dédiée à la recherche de naines brunes et de quasars à grand décalage vers le rouge. En tant que seul membre de la collaboration à travailler à plein temps sur le projet, j'ai toutefois été amené à m'impliquer fortement dans presque toutes les facettes du projet. En parallèle du travail scientique que je présente dans ce manuscript, j'ai consacré une part importante de ma thèse à la coordination du travail entre les différentes personnes impliquées dans le CFBDS de par le monde. Dans le chapitre 1, je fais un récapitulatif rapide de l'ensemble des avancées scientiques dans le domaine des naines brunes avant la présente thèse. Le chapitre 2 présente le Canada- France Brown Dwarf Survey, qui fournit les données au coeur de mon travail, ainsi que notre stratégie d'analyse. Le chapitre 3 détaille le pipeline que j'ai mis en place pour identier au mieux les quelques centaines d'astres qui nous intéressent parmi les dizaines de millions de sources que comptent les images du CFBDS. Ce chapitre met aussi en évidence les performances de la fonctionnalité d'analyse d'image par ajustement de fonction d'étalement du point -PSF- que j'ai adjointe au logiciel Source Extractor. Les candidats ainsi identiés sur la base de leur photométrie sont présentés dans le chapitre 4. Dans ce chapitre je décris mes méthodes d'estimation des biais statistiques du CFBDS, ainsi que la fonction de luminosité des naines brunes du champ que nous en avons extraite. Enn le chapitre 5 donne une revue détaillée des informations contenues dans le spectre des naines brunes. J'y présente ensuite nos observations spectroscopiques ainsi que les résultats associés, notamment la découverte d'absorption par l'ammoniac dans le spectre de la naine brune la plus froide publiée à ce jour, CFBDS0059, ainsi que la découverte de la première naine T sous-métallique.
31
Hill, David T. "The optical and NIR luminous energy output of the Universe : the creation and utilisation of a 9 waveband consistent sample of galaxies using UKIDSS and SDSS observations with the GAMA and MGC spectroscopic datasets." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1696.
Abstract:
Theories of how galaxies form and evolve depend greatly on constraints provided by observations. However, when those observations come from different datasets, systematic offsets may occur. This causes difficulties measuring variations in parameters between filters. In this thesis I present the variation in total luminosity density with wavelength in the nearby Universe (z<0.1), produced from a consistent reanalysis of NIR and optical observations, taken from the MGC, UKIDSS and SDSS surveys. I derive luminosity distributions, best-fitting Schechter function parameterisations and total luminosity densities in ugrizYJHK, and compare the variation in luminosity density with cosmic star formation history (CSFH) and initial mass function (IMF) models. I examine the r band luminosity distribution produced using different aperture definitions, the joint luminosity- surface brightness (bivariate brightness) distribution in ugrizYJHK, comparing them to previously derived distributions, and how the total luminosity density varies with wavelength when surface brightness incompleteness is accounted for. I find the following results. (1) The total luminosity density calculated using a non-Sersic (e.g. Kron or Petrosian) aperture is underestimated by at least 15%, (2) Changing the detection threshold has a minor effect on the best-fitting Schecter parameters, but the choice of Kron or Petrosian apertures causes an offset between datasets, regardless of the filter used to define the source list, (3) The decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag, and best-fitting Schechter parameters from total magnitude photometric systems have a flatter faint-end slope than Kron or Petrosian photometry, (4) There is no surface brightness distribution evolution with luminosity for luminous galaxies, but at fainter magnitudes the distribution broadens and the peak surface brightness dims. A Choloniewski function that is modified to account for this surface brightness evolution fits the bivariate-brightness distribution better than an unmodified Choloniewski function, (5) The energy density per unit interval, vf(v) derived using MGC and GAMA samples agrees within 90% confidence intervals, but does not agree with predictions using standard CSFH and IMF models. Possible improvements to the data and alterations to the theory are suggested.
32
Ibrahim, Ayman Wagdy Mohamed. "Predicting glare in open-plan offices using simplified data acquisitions and machine learning algorithms." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/204266/1/Ayman%20Wagdy%20Mohamed_Ibrahim_Thesis.pdf.
Abstract:
Glare in open-plan offices can negatively affect the productivity and well-being of office workers. Accurate glare prediction is challenging, as occupants' sensitivity to glare may differ under the same conditions. Developed as part of an ARC Linkage Project, this thesis challenges the limitations prevalent in current glare metrics by delivering a new model of predicting glare for open-plan offices. By utilising machine learning (ML) techniques, more accurate tools and methods are unlocked to assist architects and lighting engineers in the early stages of the design process. They ultimately enable more efficient daylit office designs with reduced glare discomfort in Australia.
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Hermes, James Joseph Jr. "Gravitational waves, pulsations, and more : high-speed photometry of low-mass, He-core white dwarfs." 2013. http://hdl.handle.net/2152/21608.
Abstract:
This dissertation is an observational exploration of the exciting physics that can be enabled by high-speed photometric monitoring of extremely low-mass (< 0.25 M[subscript sun symbol]) white dwarf stars, which are found in some of the most compact binaries known. It includes the cleanest indirect detection of gravitational waves at visible wavelengths, the discovery of pulsations in He-core WDs, the strongest evidence for excited p-mode pulsations in a WD, the discovery of the first tidally distorted WDs and their use to constrain the low-end of the WD mass-radius relationship, and the strongest cases of Doppler beaming observed in a binary system. It is the result of the more than 220 nights spent at McDonald Observatory doing high-speed photometry with the Argos instrument on the 2.1 m Otto Struve telescope, which has led to a number of additional exciting results, including the discovery of an intermediate timescale in the evolution of cooling DA WDs and the discovery of the most massive pulsating WD, which should have an ONe-core and should be highly crystallized.text
34
Buxton, Michelle Maree. "Optical and infrared observations of low-mass X-ray binaries with black hole candidates." Phd thesis, 2002. http://hdl.handle.net/1885/148662.
35
Theissen, Christopher. "Low-mass stars with extreme mid-infrared excesses: potential signatures of planetary collisions." Thesis, 2018. https://hdl.handle.net/2144/31675.
Abstract:
I investigate the occurrence of extreme mid-infrared (MIR) excesses, a tracer of large amounts of dust orbiting stars, in low-mass stellar systems. Extreme MIR excesses, defined as an excess IR luminosity greater than 1% of the stellar luminosity (L_IR/L∗ > 0.01), have previously only been observed around a small number of solar-mass (M⊙) stars. The origin of this excess has been hypothesized to be massive amounts of orbiting dust, created by collisions between terrestrial planets or large planetesimals. Until recently, there was a dearth of low-mass (M∗ < 0.6M⊙) stars exhibiting extreme MIR excesses, even though low-mass stars are ubiquitous (~70% of all stars), and known to host multiple terrestrial planets (~3 planets per star).
I combine the spectroscopic sample of low-mass stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 (70,841 stars) with MIR photometry from the Wide-field Infrared Survey Explorer (WISE), to locate stars exhibiting extreme MIR excesses. I find the occurrence frequency of low-mass field stars (stars with ages > 1 Gyr) exhibiting extreme MIR excesses is much larger than that for higher-mass field stars (0.41 ± 0.03% versus 0.00067 ± 0.00033%, respectively).
In addition, I build a larger sample of low-mass stars based on stellar colors and proper motions using SDSS, WISE, and the Two-Micron All-Sky Survey (8,735,004 stars). I also build a galactic model to simulate stellar counts and kinematics to estimate the number of stars missing from my sample. I perform a larger, more complete study of low-mass stars exhibiting extreme MIR excesses, and find a lower occurrence frequency (0.020 ± 0.001%) than found in the spectroscopic sample but that is still orders of magnitude larger than that for higher-mass stars. I find a slight trend for redder stars (lower-mass stars) to exhibit a higher occurrence frequency of extreme MIR excesses, as well as a lower frequency with increased stellar age.
Lastly, I use white dwarf and low-mass star binary systems to investigate if the frequency of planetary collisions (traced through extreme MIR excesses) are increased in these environments. I find that these binary systems are more likely to host collisional debris, and therefore exhibit increased excess MIR flux, over single stars. These samples probe important questions into the habitability of worlds discovered around low-mass stars.
36
Razim, Oleksandra. "Improving the reliability of photometric redshift catalogues with Self-Organizing Maps." Tesi di dottorato, 2021. http://www.fedoa.unina.it/13280/1/Razim_Thesis.pdf.
Abstract:
The already existing and upcoming massive surveys, such as KiDS, DES, Euclid and LSST, bring to reality many exiting possibilities in precision cosmology, as well as galaxy evolution and large-scale structure studies. However, to fully benefit from these surveys, we require redshifts for millions of galaxies. Currently, it is impossible to obtain these redshifts with spectroscopy only, since it would require immense observational time. For this reason, an alternative method, called photometric redshifts (photo-z) is used.
This thesis is dedicated to a new data cleaning methodology, that allows to significantly improve the quality of photo-z catalogues and to guarantee the reliability of their quality metrics (i.e., to perform photo-z calibration). This methodology is based on an unsupervised Machine Learning (ML) algorithm called Self-Organizing Maps (SOM). Different components of this methodology allow to tackle several important issues. Namely, in-cell SOM anomaly detection helps to alleviate contamination of a spectral redshift catalogue with unreliable measurements and reduce the percentage of catastrophic outliers in photo-z predictions. Another approach, SOM occupation map calibration, counters the deterioration of the reliability of photo-z catalogues caused by differences between the parameter space of the train and run datasets.
The methodology is tested on a deep 30-band photometric catalogue COSMOS2015. Photometric redshifts for this catalogue were obtained using a well-tested supervised ML algorithm MLPQNA. For additional comparison, SED (Spectral Energy Distribution) fitting photo-z were used. For both photo-z methods, the usage of the SOM-based data cleaning methodology reduces the percentage of catastrophic outliers by at least an order with corresponding improvements of other metrics. This result makes the SOM-based data cleaning a highly recommendable tool for preparing photo-z catalogues for the upcoming large surveys.
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Tagare, Hemant D. "A theory of photometric stereo for a general class of reflectance maps." Thesis, 1990. http://hdl.handle.net/1911/16396.
Abstract:
Photometric stereo is an image processing technique for 2$1\over 2$ dimensional surface reconstruction from local shading. The classical theory of photometric stereo has been developed only for surfaces that reflect in a Lambertian plus specular manner. However, there is plenty of experimental evidence that most real-world surfaces are not Lambertian plus specular.
This thesis develops the theory of photometric stereo for non-Lambertian surfaces. First, based on the physics of reflection and scattering, a general class of reflectance maps is proposed. This class is shown to model real world data more accurately than the Lambertian model. Then, the normalized photometric stereo equation using these reflectance maps is analyzed and conditions for a globally unique solution for the equation are obtained. Furthermore, the un-normalized photometric stereo equation is studied and conditions for getting a globally unique solution using only three light sources are identified. The problem of jointly estimating the reflectance map and the surface normal is proposed and shown to be ill-posed. A regularized solution to the problem is demonstrated. Finally, it is shown that extra light sources are needed to obtain a complete reconstruction of the surface, and the number of new light sources needed to achieve this is identified.
38
Bean, Keri Marie. "Determining Nighttime Atmospheric Optical Depth Using Mars Exploration Rover Images." Thesis, 2013. http://hdl.handle.net/1969.1/151097.
Abstract:
Martian clouds and dust play an important part of the radiative transfer and energy balance budget. To assist in fully understanding the impact of clouds and dust, the complete diurnal cycle needs to be characterized. One of the best methods to track diurnal variations on Mars is by measuring optical depth. The spatial and temporal trends of optical depth give insight into the dust and water cycles of the Martian atmosphere.
Until now, spacecraft could only obtain optical depth during the day. In this thesis, nighttime images from the Mars Exploration Rover Spirit are used to calculate nighttime optical depth using photometric methods to capture star flux. Bright stars in well-known constellations are used in this analysis. The observed flux was compared to the expected flux to give nighttime optical depth values. The observed nighttime optical depth was consistently similar to the daytime optical depth values on both an individual image and sol-averaged basis.
Recommendations are made going forward to use the Mars Science Laboratory Curiosity for conducting an optimal nighttime optical depth campaign to fully characterize the diurnal dust and water cycles of Mars. The Curiosity rover is well suited for nighttime imaging and can potentially provide valuable insight into the nighttime dust and cloud trends.
39
Chatterjee, Avishek. "Geometric Calibration and Shape Refinement for 3D Reconstruction." Thesis, 2015. https://etd.iisc.ac.in/handle/2005/4546.
Abstract:
This thesis is a contribution towards the methods of 3D reconstruction in computer vision.
Most of the 3D reconstruction methods are based on either the principle of triangulation or
the principle of photometry. In this thesis, we investigate both of these approaches. Although,
fundamentals of these principles are well known in computer vision, the recent availability of
new hardware and easy access to the community photo collections have made it possible to investigate some of these methods in a newer context. This is because, the existing methods of 3D reconstruction are required to be modified to cope with the new types of data available by virtue of the current advancements. In this thesis, we propose some novel approaches for 3D reconstruction that improve or combine these methods in accordance with the current advancements.
Broadly speaking, we address two themes in the area of 3D reconstruction: (a) Geometric
calibration methods for localizing a set of cameras or scanners and (b) methods for refining 3D
shapes obtained from depth scanners.
First, we present a solution to the problem of relative-rotation averaging that occurs in
the context of `structure-from-motion' (SfM). Our approach leverages the geometric Lie-group
structure of 3D rotations and incorporates robustness into our estimation method in a principled fashion. Our approach is robust, efficient and can easily handle large-scale problems. The optimality of the method is also analyzed. This approach is the state-of-the-art and is now incorporated into many libraries for SfM. A related problem is one of averaging relative Euclidean motions which occurs in the context of 3D reconstruction using depth scans. We demonstrate the robustness and the efficacy of our approach for 3D reconstruction of real-world models.
Second, we present two approaches to improve the quality of 3D scans obtained using
commercial structured-light-stereo scanners, i.e. depth cameras. In the first instance, we carry
out a sensitivity analysis of the noise inherent in such scanners. We demonstrate the use of this
sensitivity analysis in improving the performance of 3D reconstruction pipelines. In the second
instance, we exploit the complementary qualities of 3D estimates obtained from structured-light-stereo scanners and photometric methods. While structured-light-stereo scanners have coarse level _fidelity, photometric approaches contain _ne-scale 3D details. We develop a robust and accurate method of fusing these two approaches to combine the advantages of both these methods.
40
Gonzalez, Elizabeth Johana. "Observación y análisis de sistemas astrofísicos usando fenómenos de lentes gravitacionales." Doctoral thesis, 2017. http://hdl.handle.net/11086/5850.
Abstract:
Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2017.Presentamos el desarrollo de un código destinado al análisis de imágenes fotométricas para la determinación de masas de sistemas de galaxias, mediante el fenómeno de lente débil. Luego de ser testeado en una serie de imágenes simuladas, analizamos una muestra de cúmulos de galaxias de baja luminosidad en rayos-X. Obtuvimos una buena correlación entre las masas de lentes estimadas y las luminosidades de rayos-X, la cual se corresponde con otras determinaciones de esta relación. Para aquellos sistemas con mayor relación señal-ruido, estimamos la distribución de densidad identificándose un candidato a cúmulo en interacción. Además, analizamos una extensa muestra de grupos y cúmulos de galaxias utilizando técnicas de apilamiento, para la cual se estudio la relación masa-riqueza y se vinculó con la distribución de ocupación de halos. Finalmente, presentamos resultados preliminares sobre el análisis de un cúmulo de galaxias recientemente clasificado como candidato a sistema en interacción.
We present the developenent of a pipeline for the lensing analysis of ground-based images to obtain the masses of galaxy systems. After it was tested in simulated data we analized a sample low X-ray luminosity galaxy clusters. The correlation between our weak lensing mass determinations and the X-ray luminosities is suitably fitted by other estimations of the mass-luminosity relations. For the systems with larger signal-to-noise ratio, we derive the density distribution, from which we detect a possible merging system. Also, we analyzed a large sample of groups and clusters of galaxies using stacking techniques. For this sample we derive the mass-richness relation and we compare it with the halo occupation distribution. Finally, we present preliminary results of the analysis of a galaxy cluster recently classified as a possible interacting system.
41
Giammichele, Noemi. "Analyse des paramètres atmosphériques des étoiles naines blanches dans le voisinage solaire." Thèse, 2010. http://hdl.handle.net/1866/4871.
Abstract:
Ce mémoire présente une analyse homogène et rigoureuse de l’échantillon d’étoiles naines blanches situées à moins de 20 pc du Soleil. L’objectif principal de cette étude est d’obtenir un modèle statistiquement viable de l’échantillon le plus représentatif de la population des naines blanches. À partir de l’échantillon défini par Holberg et al. (2008), il a fallu dans un premier temps réunir le plus d’information possible sur toutes les candidates locales sous la forme de spectres visibles et de données photométriques. En utilisant les modèles d’atmosphère de naines blanches les plus récents de Tremblay & Bergeron (2009), ainsi que différentes techniques d’analyse, il a été permis d’obtenir, de façon homogène, les paramètres atmosphériques (Teff et log g) des naines blanches de cet échantillon. La technique spectroscopique, c.-à-d. la mesure de Teff et log g par l’ajustement des raies spectrales, fut appliquée à toutes les étoiles de notre échantillon pour lesquelles un spectre visible présentant des raies assez fortes était disponible. Pour les étoiles avec des données photométriques, la distribution d’énergie combinée à la parallaxe trigonométrique, lorsque mesurée, permettent de déterminer les paramètres atmosphériques ainsi que la composition chimique de l’étoile. Un catalogue révisé des naines blanches dans le voisinage solaire est présenté qui inclut tous les paramètres atmosphériques nouvellement determinés. L’analyse globale qui en découle est ensuite exposée, incluant une étude de la distribution de la composition chimique des naines blanches locales, de la distribution de masse et de la fonction luminosité.We present improved atmospheric parameters of nearby white dwarfs lying within 20 pc of the Sun. The aim of the current study is to obtain the best statistical model of the least-biased sample of the white dwarf population. A homogeneous analysis of the local population is performed combining detailed spectroscopic and photometric analyses based on improved model atmosphere calculations for various spectral types including DA, DB, DQ, and DZ stars. The spectroscopic technique is applied to all stars in our sample for which optical spectra are available. Photometric energy distributions, when available, are also combined to trigonometric parallax measurements to derive effective temperatures, stellar radii, as well as atmospheric compositions. A revised catalog of white dwarfs in the solar neighborhood is presented. We provide for the first time a comprehensive analysis of the mass distribution and the chemical distribution of white dwarf stars in a volume-limited sample.