An upper boundary in the mass-metallicity plane of exo-Neptunes

With the progress of detection techniques, the number of low-mass and small-size exoplanets is increasing rapidly. However their characteristics and formation mechanisms are not yet fully understood. The metallicity of the host star is a critical parameter in such processes and can impact the occurence rate or physical properties of these planets. While a frequency-metallicity correlation has been found for giant planets, this is still an ongoing debate for their smaller counterparts. Using the published parameters of a sample of 157 exoplanets lighter than 40 Mearth, we explore the mass-metallicity space of Neptunes and Super-Earths. We show the existence of a maximal mass that increases with metallicity, that also depends on the period of these planets. This seems to favor in situ formation or alternatively a metallicity-driven migration mechanism. It also suggests that the frequency of Neptunes (between 10 and 40 Mearth) is, like giant planets, correlated with the host star metallicity, whereas no correlation is found for Super-Earths (<10 Mearth).Comment: Accepted in MNRAS, 11 pages, 5 figure

SOPHIE velocimetry of Kepler transit candidates XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator

We present the detection and characterization of the transiting warm Jupiter KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We combine the analysis of Kepler photometry with Doppler spectroscopy and line-profile tomography of time-series spectra obtained with the SOPHIE spectrograph to establish its planetary nature and derive its properties. To derive reliable estimates for the uncertainties on the tomographic model parameters, we devised an empirical method to calculate statistically independent error bars on the time-series spectra. KOI-12b has a radius of 1.43$\pm$0.13$R_\mathrm{Jup}$ and a 3$\sigma$ upper mass limit of 10$M_\mathrm{Jup}$. It orbits a fast-rotating star ($v$sin$i_{\star}$ = 60.0$\pm$0.9 km s$^{-1}$) with mass and radius of 1.45$\pm$0.09 $M_\mathrm{Sun}$ and 1.63$\pm$0.15 $R_\mathrm{Sun}$, located at 426$\pm$40 pc from the Earth. Doppler tomography allowed a higher precision on the obliquity to be reached by comparison with the analysis of the Rossiter-McLaughlin radial velocity anomaly, and we found that KOI-12b lies on a prograde, slightly misaligned orbit with a low sky-projected obliquity $\lambda$ = 12.6$\stackrel{+3.0}{_{-2.9}}^\circ$. The properties of this planetary system, with a 11.4 magnitude host-star, make of KOI-12b a precious target for future atmospheric characterization.Comment: 19 pages, 10 figure

One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c

The K2 mission has recently begun to discover new and diverse planetary systems. In December 2014 Campaign 1 data from the mission was released, providing high-precision photometry for ~22000 objects over an 80 day timespan. We searched these data with the aim of detecting further important new objects. Our search through two separate pipelines led to the independent discovery of K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2 $R_\oplus$), orbiting a K dwarf extremely close to the 3:2 mean motion resonance. The two planets each show transits, sometimes simultaneously due to their proximity to resonance and alignment of conjunctions. We obtain further ground based photometry of the larger planet with the NITES telescope, demonstrating the presence of large transit timing variations (TTVs), and use the observed TTVs to place mass constraints on the transiting objects under the hypothesis that the objects are near but not in resonance. We then statistically validate the planets through the \texttt{PASTIS} tool, independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published versio

Detection and properties of exo-Neptunes and Super-Earths : synergies between SOPHIE and CHEOPS

L’amélioration des techniques de détection d’exoplanètes permet à present de sonder des populations d’objets de plus en plus petits. Mais si plusieurs centaines de petites planètes ont été découvertes, leur détection et surtout leur caractérisation précise reste un défi. À cause de ce manque de contraintes observationnelles, cette population est encore mal connue.Ma thèse a donc porté sur la détection en vitesses radiales de planètes de faible masse avec le spectrographe SOPHIE et en préparation à la mission CHEOPS. J’ai tout d’abord mené un travail d’analyse des systématiques instrumentales de SOPHIE qui m’a permis d’améliorer sa précision à un niveau de 2 m/s. Grâce à cela j’ai pu sécuriser la nature planétaire de HD 164595 b, un Neptune sur une orbite de 40 jours autour d’une étoile très similaire au Soleil. J’ai également calculé les limites de détection et établi un bilan à mi-parcours du programme à haute précision de SOPHIE après 5 ans d’observations et plus de 3000 mesures. Le satellite CHEOPS sera dédié à la recherche de transit de planètes de faibles masses déjà détectées en vitesses radiales autour d’étoiles brillantes. En préparation à son programme d’observation, j’ai en particulier établi une liste de cibles en provenance des relevés en vitesse radiale. Ce programme pourra mener à l’identification de 3 à 9 nouvelles planètes de faible masse en transit. Je me suis également intéressé aux propriétés statistiques de cette population de petites planètes. À partir de la centaine de planètes bien caractérisées dans ce domaine de masse, j’ai mis en évidence une dépendance entre la masse maximale d’une planète de ce type et la métallicité de son étoile hôte.With the improvement of the detection techniques of exoplanets, we are able to probe populations of ever smaller objects. But if several hundreds of these small planets have been discovered, their detection and especially their precise characterization is still a challenge. Because of the lack of observatio- nal constrains, this population remains poorly known. My thesis focused on the detection in radial velocity of low mass planets with the SOPHIE spectrograph in preparation of the CHEOPS mission. I first analyzed, interpreted and corrected the instrumental systematics of SOPHIE which lead to an improvement in precision down to the 2 m/s level. Thanks to this work, I uncovered the planetary nature of HD 164595 b, a Neptune-like planet on a circular 40 days orbit around a solar twin. I also computed the detection limits and established an assessment of the high precision program on SOPHIE after 5 years of observations and more than 3000 measurements.The CHEOPS satellite will be dedicated to the search of transits of small planets already detected in radial velocities around bright stars. In order to prepare its observing program, I built a list of targets from radial velocity surveys. CHEOPS, with its high precision photometry, will then be able to to measure very accurately their radius and constrain their density. This program could lead to the identification of 3 to 9 new low mass transiting planets.I also studied the statistical properties of this low-mass planets population. Based on the hundred of planets that are well characterized in this mass regime, I uncovered a link between the maximal mass of these planets and the metallicity of their host-stars

WASP-135b : a highly irradiated, inflated hot Jupiter orbiting a G5V star

We report the discovery of a new transiting planet from the WASP survey. WASP-135b is a hot Jupiter with a radius of 1.30 pm 0.09 Rjup, a mass of 1.90 pm 0.08 Mjup and an orbital period of 1.401 days. Its host is a Sun-like star, with a G5 spectral type and a mass and radius of 0.98 pm 0.06 Msun and 0.96 pm 0.05 Rsun respectively. The proximity of the planet to its host means that WASP-135b receives high levels of insolation, which may be the cause of its inflated radius. Additionally, we find weak evidence of a transfer of angular momentum from the planet to its star.PostprintPeer reviewe

The SOPHIE search for northern extrasolar planets XVI. HD 158259: A compact planetary system in a near-3:2 mean motion resonance chain

Aims. Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the northern hemisphere. As part of this observational program, 290 radial velocity measurements of the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline. Methods. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and ℓ1 periodograms. The stellar activity was modeled as a correlated Gaussian noise and its impact on the planet detection was measured with a new technique. Results. The SOPHIE data support the detection of five planets, each with m sin i ≈ 6 M⊕, orbiting HD 158259 in 3.4, 5.2, 7.9, 12, and 17.4 days. Though a planetary origin is strongly favored, the 17.4 d signal is classified as a planet candidate due to a slightly lower statistical significance and to its proximity to the expected stellar rotation period. The data also present low frequency variations, most likely originating from a magnetic cycle and instrument systematics. Furthermore, the TESS pipeline reports a significant signal at 2.17 days corresponding to a planet of radius ≈1.2 R⊕. A compatible signal is seen in the radial velocities, which confirms the detection of an additional planet and yields a ≈2 M⊕ mass estimate. Conclusions. We find a system of five planets and a strong candidate near a 3:2 mean motion resonance chain orbiting HD 158259. The planets are found to be outside of the two and three body resonances