C. Damiani

Transiting exoplanets from the CoRoT space mission - XXIV. CoRoT-25b and CoRoT-26b: two low-density giant planets

We report the discovery of two transiting exoplanets, CoRoT-25b and CoRoT-26b, both of low density, one of which is in the Saturn mass-regime. For each star, ground-based complementary observations through optical photometry and radial velocity measurements secured the planetary nature of the transiting body and allowed us to fully characterize them. For CoRoT-25b we found a planetary mass of 0.27 similar to 0.04 M-Jup, a radius of 1.08(-0.10)(+0.3) R-Jup and hence a mean density of 0.15(-0.06)(+ 0.15) g cm(-3). The planet orbits an F9 mainsequence star in a 4.86-day period, that has a V magnitude of 15.0, solar metallicity, and an age of 4.5(-2.0) (+1.8)-Gyr. CoRoT-26b orbits a slightly evolved G5 star of 9.06 +/- 1.5-Gyr age in a 4.20-day period that has solar metallicity and a V magnitude of 15.8. With a mass of 0.52 +/- 0.05 MJup, a radius of 1.26(-0.07)(+0.13) R-Jup, and a mean density of 0.28(-0.07)(+0.09) g cm(-3), it belongs to the low-mass hot-Jupiter population. Planetary evolution models allowed us to estimate a core mass of a few tens of Earth mass for the two planets with heavy-element mass fractions of 0.52(-0.15)(+0.08) and 0.26(-0.08)(+0.05), respectively, assuming that a small fraction of the incoming flux is dissipated at the center of the planet. In addition, these models indicate that CoRoT-26b is anomalously large compared with what standard models could account for, indicating that dissipation from stellar heating could cause this size.

SOPHIE velocimetry of Kepler transit candidates. VIII. KOI-205 b: a brown-dwarf companion to a K-type dwarf

We report the discovery of the discovery of a transiting brown dwarf companion to KOI-205, a K0 main-sequence star, in a 11.720125-day period transits were detected by the Kepler space telescope, and the reflex motion of the star was measured using radial velocity observations obtained with the SOPHIE spectrograph. The atmospheric parameters of the host stars were determined from the high-resolution, high signal-to-noise ratio ESPaDOns spectra obtained for this purpose. Together with spectrophotometric recovered from the literature, these spectra indicate that the star is a mildly metallic K0 dwarf with T-eff 5237 +/- 60 K. of the companion is 39.9 +/- 1.0 M-Jup and its radius is 0.81 +/- 0.02 R-Jup, in agreement with current theoretical predictions. This is the first time a nona fide brown dwarf companion is detected in orbit around a star of this type. The formation and orbital evolution of brown dwarf companions is briefly discussed in the light of this new discovery.

SOPHIE velocimetry of Kepler transit candidates XII. KOI-1257 b: a highly eccentric three-month period transiting exoplanet

In this paper we report a new transiting warm giant planet: KOI-1257 b. It was first detected in photometry as a planet-candidate by the Kepler space telescope and then validated thanks to a radial velocity :follow-up with the SOPHIE spectrograph. It orbits its host star with a period of 86,647661 d +/- 3 s and a high eccentricity of 0.772 +/- 0.045. The planet transits the main star of a metal-rich, relatively old binary system With stars of mass of 0.99 +/- 0.05 M-circle dot and 0.70 +/- 0.07 M-circle dot for the primary and secondary, respectively. This binary system is constrained thanks to a self-consistent modelling of the Kepler transit light curve; the SOPHIE radial velocities; line bisector and full-width half maximum (FWHM) variations, and the spectral energy distribution. However, future observations are needed to confirm it. The PASTIS fully-Bayesian software was used to validate the nature of the planet and to determine which star of the binary system is the transit host. By accounting for the dilution from the binary both in photometry and in radial velocity, we find that the planet has a mass of 1.45 +/- 0.35 M-4, and a radius of 0.94(4) +/- 0.12 R-4 and thus a bulk density of 2.1 +/- 1.2 g cm(-3). The planet has an equilibrium temperature of 511 +/- 50K, making it one of the few known members of the warm-Jupiter population. The HARPS-N spectrograph was also used to observe a transit of KOI-1257 b, simultaneously with a joint amateur and professional photometric follow up, with the aim of constraining the orbital obliquity of the planet. However, the Rossiter-McLaughlin effect was not clearly detected, resulting in poor constraints on the orbital obliquity of the planet.

Evolution of angular-momentum-losing exoplanetary systems - Revisiting Darwin stability

We assess the importance of tidal evolution and its interplay with magnetic braking in the population of hot-Jupiter planetary systems. By minimizing the total mechanical energy of a given system under the constraint of stellar angular momentum loss, we rigorously find the conditions for the existence of dynamical equilibrium states. We estimate their duration, in particular when the wind torque spinning down the star is almost compensated by the tidal torque spinning it up. We introduce dimensionless variables to characterize the tidal evolution of observed hot Jupiter systems and discuss their spin and orbital states using generalized Darwin diagrams based on our new approach. We show that their orbital properties are related to the effective temperature of their host stars. The long-term evolution of planets orbiting F- and G-type stars is significantly different owing to the combined effect of magnetic braking and tidal dissipation. The existence of a quasi-stationary state, in the case of short-period planets, can significantly delay their tidal evolution that would otherwise bring the planet to fall into its host star. Most of the planets known to orbit F-type stars are presently found to be near this stationary state, probably in a configuration not too far from that they had when their host star settled on the zero-age main sequence. Considering the importance of angular momentum loss in the early stages of stellar evolution, our results indicate that it has to be taken into account also to properly test the migration scenarios of planetary system formation.

KOI-200 b and KOI-889 b: Two transiting exoplanets detected and characterized with Kepler, SOPHIE, and HARPS-N

We present the detection and characterization of the two new transiting, close-in, giant extrasolar planets KOI-200 b and KOI-889 b. They were first identified by the Kepler team as promising candidates from photometry of the Kepler satellite, then we established their planetary nature thanks to the radial velocity follow-up jointly secured with the spectrographs SOPHIE and HARPS-N. Combined analyses of the whole datasets allow the two planetary systems to be characterized. The planet KOI-200 b has mass and radius of 0.68 +/- 0.09 M-Jup and 1.32 +/- 0.14 R-Jup; it orbits in 7.34 days a F8V host star with mass and radius of 1.40(-0.11)(+0.14) M-circle dot and 1.51 +/- 0.14 R-circle dot. The planet KOI-889 b is a massive planet with mass and radius of 9.9 +/- 0.5 M-Jup and 1.03 +/- 0.06 R-Jup; it orbits in 8.88 days an active G8V star with a rotation period of 19.2 +/- 0.3 days, and mass and radius of 0.88 +/- 0.06 M-circle dot and 0.88 +/- 0.04 R-circle dot. Both planets lie on eccentric orbits and are located just at the frontier between regimes where the tides can explain circularization and where tidal effects are negligible. The two planets are among the first ones detected and characterized thanks to observations secured with HARPS-N, the new spectrograph recently mounted at the Telescopio Nazionale Galileo. These results illustrate the benefits that could be obtained from joint studies using two spectrographs as SOPHIE and HARPS-N.

SOPHIE velocimetry of Kepler transit candidates - XIII. KOI-189 b and KOI-686 b: two very low-mass stars in long-period orbits

We present the radial-velocity follow-up of two Kepler planetary transiting candidates (KOI-189 and KOI-686) carried out with the SOPHIE spectrograph at the Observatoire de Haute Provence. These data promptly discard these objects as viable planet candidates and show that the transiting objects are in the regime of very low-mass stars, where a strong discrepancy between observations and models persists for the mass and radius parameters. By combining the SOPHIE spectra with the Kepler light curve and photometric measurements found in the literature, we obtain a full characterization of the transiting companions, their orbits, and their host stars. The two companions are in significantly eccentric orbits with relatively long periods (30 days and 52.5 days), which makes them suitable objects for a comparison with theoretical models, since the effects invoked to understand the discrepancy with observations are weaker for these orbital distances. KOI-189 b has a mass M = 0.0745 +/- 0.0033 M-circle dot and a radius R = 0.1025 +/- 0.0024 R-circle dot. The density of KOI-189 b is significantly lower than expected from theoretical models for a system of its age. We explore possible explanations for this difference. KOI-189 b is the smallest hydrogen-burning star with such a precise determination of its fundamental parameters. KOI-686 b is larger and more massive (M = 0.0915 +/- 0.0043 M-circle dot; R = 0.1201 +/- 0.0033 R-circle dot), and its position in the mass-radius diagram agrees well with theoretical expectations.

Characterization of the four new transiting planets KOI-188b, KOI-195b, KOI-192b, and KOI-830b

The characterization of four new transiting extrasolar planets is presented here. KOI-188b and KOI-195b are bloated hot Saturns, with orbital periods of 3.8 and 3.2 days, and masses of 0.25 and 0.34 M-Jup. They are located in the low-mass range of known transiting, giant planets. KOI-192b has a similar mass (0.29 M-Jup) but a longer orbital period of 10.3 days. This places it in a domain where only a few planets are known. KOI-830b, finally, with a mass of 1.27 M-Jup and a period of 3.5 days, is a typical hot Jupiter. The four planets have radii of 0.98, 1.09, 1.2, and 1.08 R-Jup, respectively. We detected no significant eccentricity in any of the systems, while the accuracy of our data does not rule out possible moderate eccentricities. The four objects were first identified by the Kepler team as promising candidates from the photometry of the Kepler satellite. We establish here their planetary nature thanks to the radial velocity follow-up we secured with the HARPS-N spectrograph at the Telescopio Nazionale Galileo. The combined analyses of the datasets allow us to fully characterize the four planetary systems. These new objects increase the number of well-characterized exoplanets for statistics, and provide new targets for individual follow-up studies. The pre-screening we performed with the SOPHIE spectrograph at the Observatoire de Haute-Provence as part of that study also allowed us to conclude that a fifth candidate, KOI-219.01, is not a planet but is instead a false positive.

Transiting exoplanets from the CoRoT space mission - XXVII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit

Context. We present the discovery of two transiting extrasolar planets by the satellite CoRoT. Aims: We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars. Methods: We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g, Teff, v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical. Results: We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484 ± 0.087 MJup; radius 0.955 ± 0.066 RJup) orbiting an evolved star with an orbital period of 5.208 51 ± 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 ± 0.20 MJup; radius 0.90 ± 0.16 RJup) orbiting an oblate star with an orbital period of 2.850 570 ± 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point. Conclusions: These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29. The CoRoT space mission, launched on December 27th 2006, was developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain. Based on observations obtained with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in time allocated by OPTICON and the Spanish Time Allocation Committee (CAT). The research leading to these results has received funding from the European Communitys Seventh Framework Programme (FP7/2007-2013) under grant agreement number RG226604 (OPTICON). This work makes use of observations from the LCOGT network.Appendices are available in electronic form at http://www.aanda.org

SOPHIE velocimetry of Kepler transit candidates XIV. A joint photometric, spectroscopic, and dynamical analysis of the Kepler-117 system

As part of our follow-up campaign of Kepler planets, we observed Kepler-117 with the SOPHIE spectrograph at the Observatoire de Haute-Provence. This F8-type star hosts two transiting planets in non-resonant orbits. The planets, Kepler-117 b and c, have orbital periods

Stellar classification of CoRoT targets

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