The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way, which are inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on high-quality measurements for 7545 red giant stars within 4.5 kpc of the Galactic center, with the goal to shed light on the structure and origin of the Galactic bulge. Stellar metallicities are found, through multiple Gaussian decompositions, to be distributed in several components, which is indicative of the presence of various stellar populations such as the bar or the thin and the thick disks. Super-solar ([Fe/H] = +0.32) and solar ([Fe/H] = +0.00) metallicity components, tentatively associated with the thin disk and the Galactic bar, respectively, seem to be major contributors near the midplane. A solar-metallicity component extends outwards in the midplane but is not observed in the innermost regions. The central regions (within 3 kpc of the Galactic center) reveal, on the other hand, the presence of a significant metal-poor population ([Fe/H] = -0.46), tentatively associated with the thick disk, which becomes the dominant component far from the midplane (vertical bar Z vertical bar >= +0.75 kpc). Varying contributions from these different components produce a transition region at +0.5 kpc <= vertical bar Z vertical bar <= +1.0 kpc, characterized by a significant vertical metallicity gradient.

We present simultaneous Hubble Space Telescope (HST) WFC3+Spitzer IRAC variability monitoring for the highly variable young (similar to 20 Myr) planetary-mass object PSO J318.5-22. Our simultaneous HST + Spitzer observations covered approximately two rotation periods with Spitzer and most of a rotation period with the HST. We derive a period of 8.6. +/-. 0.1 hr from the Spitzer light curve. Combining this period with the measuredvsinifor this object, we find an inclination of 56 degrees.2. +/-. 8 degrees.1. We measure peak-to-trough variability amplitudes of 3.4%. +/-. 0.1% for Spitzer Channel 2 and 4.4%-5.8% (typical 68% confidence errors of similar to 0.3%) in the near-IR bands (1.07-1.67 mu m) covered by the WFC3 G141 prism-the mid-IR variability amplitude for PSO J318.5-22 is one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary-mass object. Additionally, we detect phase offsets ranging from 200 degrees to 210 degrees (typical error of similar to 4 degrees) between synthesized near-IR light curves and the Spitzer mid-IR light curve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.

Je présente une analyse multidisciplinaire du comportement d’une exosphère d’un satellite dont la limite inférieure est une surface solide. Une exosphère par définition n’a pas de limite supérieure, est constituée d’un gaz dont la dynamique n’est pas régie par des collisions et correspond à la région d’interaction entre un objet planétaire et sa planète mère ou étoile. Dans cette thèse, je montrerai qu’une population exosphérique d’un satellite qui serait volatile et dont la dynamique serait fortement dépendante de la température de surface, aura une évolution orbitale synchrone avec le cycle diurne. Par exemple, l’oxygène moléculaire autour d’Europa et de Ganymède, satellites de Jupiter,devrait suivre une telle évolution. Je m’attacherai donc à comparer les résultats d’un modèle 3D Monte Carlo reconstruisant l’évolution de cette exosphère et les observations d’émissions aurorales par le télescope Hubble pour souligner la persistance d’une asymétrie matin/soir caractéristique de ce cycle diurne. Par ailleurs,une analyse plus théorique de l’origine de cette asymétrie nous suggère qu’un réservoird’O2 sous forme gazeuse dans le régolite pourrait être à l’origine de la formation de cette exosphère. En plus de la description de l’O2 exosphérique autour d’Europa, je soulignerai les différences notables avec l’H2O et ses produits. Enfin, j’ai également travaillé à la caractérisation d’une nouvelle technologie pour une source d’ionisation basée sur l’utilisation de nano-tubes de carbone. Cet émetteur d’électron utilisé pour la spectrométrie de masse neutre s’avère nettement plus efficace que les émetteurs classiquement utilisés dans le spatial et devrait donc nous aider à explorer ces exosphères. / I present a multidisciplinary analysis on the behavior of asurface-bounded exosphere synchronously rotating about its primary. Anexosphere is the boundless, external envelope of gas extending from aplanetary surface or atmosphere. This collisionless gas represents theinterface between planets and stars, as it directly interacts with theinterplanetary medium. Should the exosphere possess a population ofvolatiles strongly coupled with the surface temperature, the exospherewill be capable of experiencing a diurnal cycle over an orbitalperiod. I provide the first evidence of the existence of such adiurnal cycle in the molecular oxygen exospheres of two of Jupiter’sicy moons: Europa and Ganymede. The evidence was surmounted by anin-depth comparison between the near-surface ultraviolet oxygenaurorae observations by the Hubble Space Telescope and 3-D Monte Carlosimulations of Europa’s near-surface O2 exosphere, where both auroraeand exospheres where found to be strongly peaking at dusk. Thedusk-over-dawn asymmetry analysis also provides evidence that Europamay harbor a large O2 reservoir embedded in its ice today. Inaddition to O2 , I present the first orbital simulations of all knownwater-products at Europa, and provide perspectives on discerning theeffects of cryovolcanism on the exosphere. Lastly, at LATMOS, Icharacterized a novel ionization source: a carbon nanotube electrongun (CNTeg). This in-situ device used for neutral mass spectrometry,may prove to be a very efficient electron emitter (P < 10 milliWatts)and should aid future searches to detect trace gases in any exosphere.

We present an optical eclipse observation of the hot Jupiter WASP-12b using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. These spectra allow us to place an upper limit of A(g) < 0.064 (97.5% confidence level) on the planet's white light geometric albedo across 290-570 nm. Using six wavelength bins across the same wavelength range also produces stringent limits on the geometric albedo for all bins. However, our uncertainties in eclipse depth are similar to 40% greater than the Poisson limit and may be limited by the intrinsic variability of the Sun-like host star-the solar luminosity is known to vary at the 10(-4) level on a timescale of minutes. We use our eclipse depth limits to test two previously suggested atmospheric models for this planet: Mie scattering from an aluminum-oxide haze or cloud-free Rayleigh scattering. Our stringent nondetection rules out both models and is consistent with thermal emission plus weak Rayleigh scattering from atomic hydrogen and helium. Our results are in stark contrast with those for the much cooler HD 189733b, the only other hot Jupiter with spectrally resolved reflected light observations; those data showed an increase in albedo with decreasing wavelength. The fact that the first two exoplanets with optical albedo spectra exhibit significant differences demonstrates the importance of spectrally resolved reflected light observations and highlights the great diversity among hot Jupiters.

The determination of atmospheric structure and molecular abundances of planetary atmospheres via spectroscopy involves direct comparisons between models and data. While varying in sophistication, most model spectra comparisons fundamentally assume one-dimensional (1D) model physics. However, knowledge from general circulation models and of solar system planets suggests that planetary atmospheres are inherently three-dimensional in their structure and composition. We explore the potential biases resulting from standard "1D" assumptions within a Bayesian atmospheric retrieval framework. Specifically, we show how the assumption of a single 1D thermal profile can bias our interpretation of the thermal emission spectrum of a hot Jupiter atmosphere that is composed of two thermal profiles. We retrieve spectra of unresolved model planets as observed with a combination of the Hubble Space Telescope Wide Field Camera 3 (WFC3)+Spitzer Infrared Array Camera (IRAC) as well as the James Webb Space Telescope (JWST) under varying differences in the two thermal profiles. For WFC3+IRAC, there is a significantly biased estimate of CH4 abundance using a 1D model when the contrast is 80%. For JWST, two thermal profiles are required to adequately interpret the data and estimate the abundances when contrast is greater than 40%. We also apply this preliminary concept to the recent WFC3+IRAC phase curve data of the hot Jupiter WASP-43b. We see similar behavior as present in our simulated data: while the H2O abundance determination is robust, CH4 is artificially well-constrained to incorrect values under the 1D assumption. Our work demonstrates the need to evaluate model assumptions in order to extract meaningful constraints from atmospheric spectra and motivates exploration of optimal observational setups.

abstract: Planets are generally believed to form in protoplanetary disks within a few million years (Myr) to several hundred Myr. But planetary embryos or protoplanets likely exist before disk gas dissipates (in three to ten Myr), capturing H2 -rich primary atmospheres from the nebula. Exploring these primordial atmospheres of planets provides a pathway to understanding the origins and the diversity of planets in the solar system and beyond. In this dissertation, I studied the primary atmospheres by modeling their formation, their impacts on planet formation, and determining methods to characterize them on exoplanets. First, I numerically investigated the flow structures and dynamics of the primary atmospheres accreted on Earth-sized planets with eccentric orbits. Such planets can generate atmosphere-stripping bow shocks, as their relative velocities to the gas are generally supersonic. The atmospheres are three to four orders of magnitude less massive than those of planets with circular orbits. Hydrodynamic simulations also revealed large-scale recycling gas flow in the post-shock regions. This study provides important insights into the impacts of migration and scattering on primary atmospheres. Second, I looked into how the presence of the primary atmosphere affects the trajectories of chondrule precursors passing through a planetary bow shock. To determine what magnetic fields chondrules were exposed to as they cooled below their Curie points, I computed the gas properties and magnetic diffusion rates in the bow shock region of a planet with and without the primary atmosphere. I concluded that, if melted in planetary bow shocks, most chondrules were cooled in the far downstream and they probably recorded the background nebular field. Last, I studied the characterization of cloudy primary atmospheres on exoplanets using a Bayesian retrieval approach. I focused on obtaining bulk cloud properties and the impact of clouds on constraining various atmospheric properties through transmission spectroscopy using the James Webb Space Telescope (JWST). Most key atmospheric and cloud inferences can be well constrained in the wavelength range (0.6 – 11 µ m) but there are different optimal wavelengths for constraining atmosphere or cloud parameters. Other results including degeneracies among cloud parameters can also serve as a guideline for future observers. / Dissertation/Thesis / Doctoral Dissertation Astrophysics 2020

No description available.

Limb darkening is a fundamental ingredient for interpreting observations of planetary transits, eclipsing binaries, optical/infrared interferometry and microlensing events. However, this modeling traditionally represents limb darkening by a simple law having one or two coefficients that have been derived from plane-parallel model stellar atmospheres, which has been done by many researchers. More recently, researchers have gone beyond plane-parallel models and considered other geometries. We previously studied the limb-darkening coefficients from spherically symmetric and plane-parallel model stellar atmospheres for cool giant and supergiant stars, and in this investigation we apply the same techniques to FGK dwarf stars. We present limb-darkening coefficients, gravity-darkening coefficients and interferometric angular diameter corrections from Atlas and SAtlas model stellar atmospheres. We find that sphericity is important even for dwarf model atmospheres, leading to significant differences in the predicted coefficients.

Limb darkening is a fundamental ingredient for interpreting observations of planetary transits, eclipsing binaries, optical/infrared interferometry and microlensing events. However, this modeling traditionally represents limb darkening by a simple law having one or two coefficients that have been derived from plane-parallel model stellar atmospheres, which has been done by many researchers. More recently, researchers have gone beyond plane-parallel models and considered other geometries. We previously studied the limb-darkening coefficients from spherically symmetric and plane-parallel model stellar atmospheres for cool giant and supergiant stars, and in this investigation we apply the same techniques to FGK dwarf stars. We present limb-darkening coefficients, gravity-darkening coefficients and interferometric angular diameter corrections from Atlas and SAtlas model stellar atmospheres. We find that sphericity is important even for dwarf model atmospheres, leading to significant differences in the predicted coefficients.

No description available.