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

The four longest period Kuiper Belt objects have orbital periods close to integer ratios with each other. A hypothetical planet with an orbital period of similar to 17,117 years and a semimajor axis similar to 665 au would have N/1 and N/2 period ratios with these four objects. The orbital geometries and dynamics of resonant orbits constrain the orbital plane, the orbital eccentricity, and the mass of such a planet as well as its current location in its orbital path.

In the coming years, high-contrast imaging surveys are expected to reveal the characteristics of the population of wide-orbit, massive, exoplanets. To date, a handful of wide planetary mass companions are known, but only one such multi-planet system has been discovered: HR 8799. For low mass planetary systems, multi-planet interactions play an important role in setting system architecture. In this paper, we explore the stability of these high mass, multi-planet systems. While empirical relationships exist that predict how system stability scales with planet spacing at low masses, we show that extrapolating to super-Jupiter masses can lead to up to an order of magnitude overestimate of stability for massive, tightly packed systems. We show that at both low and high planet masses, overlapping mean-motion resonances trigger chaotic orbital evolution, which leads to system instability. We attribute some of the difference in behavior as a function of mass to the increasing importance of second order resonances at high planet-star mass ratios. We use our tailored high mass planet results to estimate the maximum number of planets that might reside in double component debris disk systems, whose gaps may indicate the presence of massive bodies.

The Pluto-Charon system has come into sharper focus following the flyby of New Horizons. We use N-body simulations to probe the unique dynamical history of this binary dwarf planet system. We follow the evolution of the debris disc that might have formed during the Charon-forming giant impact. First, we note that in situ formation of the four circumbinary moons is extremely difficult if Charon undergoes eccentric tidal evolution. We track collisions of disc debris with Charon, estimating that hundreds to hundreds of thousands of visible craters might arise from 0.3-5 km radius bodies. New Horizons data suggesting a dearth of these small craters may place constraints on the disc properties. While tidal heating will erase some of the cratering history, both tidal and radiogenic heating may also make it possible to differentiate disc debris craters from Kuiper belt object craters. We also track the debris ejected from the Pluto-Charon system into the Solar system; while most of this debris is ultimately lost from the Solar system, a few tens of 10-30 km radius bodies could survive as a Pluto-Charon collisional family. Most are plutinos in the 3: 2 resonance with Neptune, while a small number populate nearby resonances. We show that migration of the giant planets early in the Solar system's history would not destroy this collisional family. Finally, we suggest that identification of such a family would likely need to be based on composition as they show minimal clustering in relevant orbital parameters.

Comprendre le processus de formation stellaire est un objectif majeur en astronomie. Sur ce sujet les observations ne donnent que très peu d'information, et les modèles numériques sont donc naturellement privilégiés. De tels modèles s'attachent à suivre la dynamique du gaz, sous l'effet de processus physique variés, ce qui nécessite un temps de calcul très important et ne permet pas de modéliser l'évolution au delà de 0.2 Myr environ. Or les résultats observationnels sont essentiellement issus du champ galactique proche, des amas évolués, voire des regions jeunes ou associations d'étoiles, dont l'âge peut varier de 1 Myr à quelques Gyr. Par conséquent, il est nécessaire pour comparer les résultats des modèles aux observations de comprendre ce qu'il se passe durant cet intervalle de temps. La formation stellaire tend à produire des étoiles en groupes, à partir de l'effondrement gravitationnel d'un nuage moléculaire turbulent. A mesure que les étoiles se forment, le gaz est éjecté et l'évolution est dominée par les interactions gravitationnelles. Suivre l'évolution sous l'effet de ces interactions est couramment utilisé afin de contraindre les modèles et de mieux comprendre l'origine des populations stellaires observées. Les étoiles se forment en sous-groupes ou structures hiérarchisées, qui peuvent ensuite fusionner pour donner des amas stellaires proche des amas ouverts, ou au contraire finir en associations distinctes. Dans ma thèse, je me suis intéressé à l'évolution dynamique de petits groupes d'étoiles, jusqu'alors peu étudiés par rapport aux groupes à 1000 ou 10^4 étoiles. J'ai simulé l'évolution de groupes à N < 100, dans le but d'en étudier la dynamique d'un point de vue statistique, grâce notamment au grand nombre de simulations effectuées, et afin d'identifier les signatures observationnelles propres à une situation initiale donnée. A partir d'un grand nombre de configurations initiales (avec N=20, 50, 100, un rayon typique de 0.025 pc à 1 pc) et 500 simulations par configurations, j'ai étudié l'évolution dynamique de groupes composés d'étoiles de même masse ou comprenant un spectre de masse, et sans population de binaire initiale. L'évolution de tels groupes s'est révélée similaire à celle de groupes plus grands, mais avec une phase d'effondrement plus rapide et surtout moins prononcée. Je décris le comportement moyen menant à une lente expansion de l'amas, ainsi qu'une voie d'évolution très différente, apparaissant dans 17% des cas étudiés, où l'amas est complètement dispersé suite à l'éjection d'une binaire centrale serrée. J'ai également recherché dans quelle mesure les données en densité et en vitesse 3D pouvaient permettre d'identifier l'état dynamique initial d'un groupe. L'utilisation de ces seules données suffisait dans certain cas à déterminer la densité initiale, mais elles devraient être complétées par des données concernant la population de binaire. Ce travail pourra être mis en application pour étudier l'origine dynamique d'association ou de groupes stellaires connus. Enfin, j'ai effectué un grand nombre de simulations numériques dans le but de reproduire l'état observé de l'amas eta Chamaeleontis par pure évolution dynamique à partir de conditions initiales standards. Cette association présente des caractéristiques d'amas évolué, telle que son spectre de masse pauvre en objets de faible masse et l'absence de binaires larges. Je montre que ces propriétés ne peuvent pas être reproduites uniquement par la dynamique, et sont donc les traces d'un processus de formation non standard. / Understanding the star formation process is a key issue in astronomy. Since direct observation provide only very limited information, this issue is investigated by models. Such models need to take into account complex physical processes while following the gas dynamics, so that simulations need a lot of time to run and do not follow the star formation process for longer than 0.2 Myr. The best known observational results concerns the field population, evolved open clusters or younger clusters or associations, which are between 1 Myr and a few Gyr old. Therefore in order to compare the results from models to known observations, we need to bridge the gap between the two. Star formation appears to produce groups of stars from the collapse of turbulent molecular clouds. As stars form, the gas is progressively ejected from the cluster, and the evolution is dominated by gravitational interactions. Following the dynamical evolution of a group of star using N-Body codes is a standard way used to constraint the models and understand the origin of the different populations. Star formation may produce sub-structure or small groups that merge to form bigger entities, or end up as loose association. In my thesis I focused on the dynamics of small groups, that have not been investigated as thoroughly as 1000 or 10^4 star groups. I performed N-Body simulations of small stellar groups, with N<100, in order to study their dynamics using a statistical approach, made possible by running a large number of simulations, and to find some observational signatures of given initial conditions. This approach enable to take full account of stochastic effects due to dynamical interactions. Using a large number of initial configurations (with N=20, 50, 100, a typical radius from 0.025 pc to 1 pc) and a sample of 500 simulations per configuration, I looked at equal mass groups as well as groups having a mass spectrum, without any binary initially. Such small groups show similar evolution to bigger groups, but with faster and less pronounced collapse phase. I described the average behaviour of slow expansion of the cluster, and an alternative evolution, occurring with 17% probability, that ended in the complete dissolution of the group due to ejection of a central binary. Searching for a way to identify the initial configuration from observational measure, I looked at the complementarity of density and 3D velocity and was able to show that it could be sufficient in some cases to determine the initial density. Further investigations are needed to take into account the information on the binary population and will be used to investigate the formation of known associations or young regions. Finally, I ran a large number of simulations, aiming at reproducing the observed state of the eta Chamaeleontis from standard initial conditions and pure dynamical evolution. This association properties are consistent with a dynamical evolved cluster, namely low-mass object poor and having only tight binaries. I showed that these properties cannot be reproduced with pure dynamical evolution from standard initial mass function and binary population, meaning that its particular features must have been pristine.

Mean motion resonances (MMRs) play an important role in the formation and evolution of planetary systems and have significantly influenced the orbital properties and distribution of planets and minor planets in the solar system and in. exoplanetary systems. Most previous theoretical analyses have focused on the low- to moderate-eccentricity regime, but with new discoveries of high-eccentricity resonant minor planets and even exoplanets, there is increasing motivation to examine MMRs in the high-eccentricity regime. Here we report on a study of the high-eccentricity regime of MMRs in the circular planar restricted three-body problem. Numerical analyses of the 2: 1 and the 3: 2 interior resonances are carried out for a wide range of planet-to-star mass ratio mu, and for a wide range of eccentricity of the test particle. The surface-of-section technique is used to study the phase space structure near resonances. We find that new stable libration zones appear at higher eccentricity at libration centers that are. shifted from those at low eccentricities. We provide physically intuitive explanations for these transitions in phase space, and we present novel results on the mass and eccentricity dependence of the resonance widths. Our results show that MMRs have sizable libration zones at high eccentricities, comparable to those at lower eccentricities.

In this dissertation, we present three complementary studies of the processes that drive planetary migration. The first is a radial-velocity survey in search of giant planets in adolescent (<1 >Gyr) open clusters. While several different mechanisms may act to drive giant planets inward, only some mechanisms will excite high eccentricities while doing so. Measuring the eccentricities of young hot Jupiters in these clusters (at a time before the orbits have had a chance to circularize due to tidal friction with their host stars) will allow us to identify which mechanisms are most important. Through this survey, we detect the first 3 hot Jupiters in open clusters (and at least 4 long-period planets), and we measure the occurrence rate of hot Jupiters in clusters to be similar to that of the field (~1%). We determine via analyses of hot Jupiter eccentricities and outer companions in these systems that high eccentricity migration mechanisms (those requiring the presence of a third body) are important for migration. The second project, an adaptive optics imaging survey for stellar companions to known hot Jupiter hosts, aims to determine the role that stellar companions in particular play in giant planet migration. Through a preliminary analysis, we derive a lower limit on the binary frequency of 45% (greater than that of the typical field star), and we find that the presence of a companion is correlated with misalignment of the spin-orbit angle of the planetary system, as would be expected for stellar Kozai-Lidov migration: at least 74% of misaligned systems reside in binaries. We thus conclude that among high eccentricity migration mechanisms, those requiring a stellar companion play a significant role. Finally, we describe simulations of measurements of the planet population expected to be discovered by TESS, and use these to demonstrate that a strong constraint on the obliquity distribution of small planets can be derived using only TESS photometry, Gaia astrometry, and vsin(i) measurements of the host stars. This obliquity distribution will be a key piece of evidence to help detemine the likely formation and migration histories of small planets, and can contribute to the assessment of the potential for Earth-like planets to harbor life.

Stellar companions can influence the formation and evolution of planetary systems, but there are currently few observational constraints on the properties of planet-hosting binary star systems. We search for stellar companions around 77 transiting hot Jupiter systems to explore the statistical properties of this population of companions as compared to field stars of similar spectral type. After correcting for survey incompleteness, we find that 47% +/- 7% of hot Jupiter systems have stellar companions with semimajor axes between 50 and 2000 au. This is 2.9 times larger than the field star companion fraction in this separation range, with a significance of 4.4 sigma. In the 1-50 au range, only 3.9(-2.0)(+4.5)% of hot Jupiters host stellar companions, compared to the field star value of 16.4% +/- 0.7%, which is a 2.7 sigma difference. We find that the distribution of mass ratios for stellar companions to hot Jupiter systems peaks at small values and therefore differs from that of field star binaries which tend to be uniformly distributed across all mass ratios. We conclude that either wide separation stellar binaries are more favorable sites for gas giant planet formation at all separations, or that the presence of stellar companions preferentially causes the inward migration of gas giant planets that formed farther out in the disk via dynamical processes such as Kozai-Lidov oscillations. We determine that less than 20% of hot Jupiters have stellar companions capable of inducing Kozai-Lidov oscillations assuming initial semimajor axes between 1 and 5 au, implying that the enhanced companion occurrence is likely correlated with environments where gas giants can form efficiently.

No description available.

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet's atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet-star interactions in HAT-P-2's eccentric planetary system gained from the analysis of similar to 350 hr of 4.5 mu m observations with the Spitzer Space Telescope. The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2b's 4.5 mu m photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet's orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.