A. S. Bonomo

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.

Transiting exoplanets from the CoRoT space mission - XV. CoRoT-15b: a brown-dwarf transiting companion

We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12 +0.30 ―0.15 R Jup and a mass of 63.3 ± 4.1 M Jup , and is thus the second transiting companion lying in the theoretical mass domain of brown dwarfs. CoRoT-15b is either very young or inflated compared to standard evolution models, a situation similar to that of M-dwarf stars orbiting close to solar-type stars. Spectroscopic constraints and an analysis of the lightcurve imply a spin period in the range 2.9-3.1 days for the central star, which is compatible with a double-synchronisation of the system.

SOPHIE velocimetry of Kepler transit candidates III. KOI-423b: an 18 Mjup transiting companion around an F7IV star

We report the strategy and results of our radial velocity fol low-up campaign with the SOPHIE spectrograph (1.93-m OHP) of four transiting planetary candidates discovered by the Kepler space mission. We discuss the selection of the candidates KOI-428, KOI-410, KOI-552, and KOI-423. KOI-428 was established as a hot Jupiter transiting the largest and the most evolved star discover ed so far and is described by Santerne et al. (2011a). KOI-410 does not present radial velocity change greater than 120 m s −1 , which allows us to exclude at 3σ a transiting companion heavier than 3.4 MJup. KOI-552b appears to be a transiting low-mass star with a mass ratio of 0.15. KOI-423b is a new transiting companion in the overlapping region between massive planets and brown dwarfs. With a radius of 1.22± 0.11 RJup and a mass of 18.0± 0.92 MJup, KOI-423b is orbiting an F7IV star with a period of 21.0874± 0.0002 days and an eccentricity of 0.12±0.02. From the four selected Kepler candidates, at least three of them have a Jupiter-size trans iting companion, but two of them are not in the mass domain of Jupiter-like planets. KOI-423b and KOI-522b are members of a growing population of known massive companions orbiting close to an F-type star. This population currently appears to be absent around G-type stars, possibly due to their rapid braking and the engulfment of their companions by tidal decay.

Transiting exoplanets from the CoRoT space mission X. CoRoT-10b: a giant planet in a 13.24 day eccentric orbit

Context. The space telescope CoRoT searches for transiting extrasolar planets by continuously monitoring the optical flux of thousands of stars in several fields of view. Aims. We report the discovery of CoRoT-10b, a giant planet on a highly eccentric orbit (e = 0.53 ± 0.04) revolving in 13.24 days around a faint (V = 15.22) metal-rich K1V star. Methods. We used CoRoT photometry, radial velocity observations taken with the HARPS spectrograph, and UVES spectra of the parent star to derive the orbital, stellar, and planetary parameters. Results. We derive a radius of the planet of 0.97 ± 0.07 RJup and a mass of 2.75 ± 0.16 MJup. The bulk density, ρp = 3.70 ± 0. 83 gc m −3 ,i s∼2.8 that of Jupiter. The core of CoRoT-10b could contain up to 240 M⊕ of heavy elements. Moving along its eccentric orbit, the planet experiences a 10.6-fold variation in insolation. Owing to the long circularisation time, τcirc > 7G yr, a resonant perturber is not required to excite and maintain the high eccentricity of CoRoT-10b.

Transiting exoplanets from the CoRoT space mission XIV. CoRoT-11b: a transiting massive "hot-Jupiter" in a prograde orbit around a rapidly rotating F-type star

The CoRoT xa0exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V xa0=xa012.9xa0mag F6 dwarf star (M ∗ xa0=xa01.27xa0±xa00.05xa0M ⊙ , R ∗ xa0=xa01.37xa0±xa00.03xa0R ⊙ , T eff xa0=xa06440xa0±xa0120xa0K), with an orbital period of P xa0=xa02.994329xa0±xa00.000011xa0days and semi-major axis a xa0=xa00.0436xa0±xa00.005xa0AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT xa0are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (v sini xa0⋆ xa0=xa040xa0±xa05xa0kmu2009s-1 ) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of M p u2009xa0=xa02.33xa0±xa00.34xa0M Jup xa0and radius R p u2009xa0=xa01.43xa0±xa00.03xa0R Jup , the resulting mean density of CoRoT-11b (ρ p xa0=xa00.99xa0±xa00.15xa0g/cm3 ) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior.

The secondary eclipse of CoRoT-1b

The transiting planet CoRoT-1b is thought to belong to the pM-class of planets, in which the thermal emission dominates in the optical wavelengths. We present a detection of its secondary eclipse in the CoRoT white channel data, whose response function goes from ∼400 to ∼1000 nm. We used two different filtering approaches, and several methods to evaluate the significance of a detection of the secondary eclipse. We detect a secondary eclipse centered within 20 min at the expected times for a circular orbit, with a depth of 0.016 ± 0.006%. The center of the eclipse is translated in a1 -σ upper limit to the planet’s eccentricity of e cos ω< 0.014. Under the assumption of a zero Bond Albedo and blackbody emission from the planet, it corresponds to a TCoRoT = 2330 +120 −140 K. We provide the equilibrium temperatures of the planet as a function of the amount of reflected light. If the planet is in thermal equilibrium with the incident flux from the star, our results imply an inefficient transport mechanism of the flux from the day to the night sides.

SOPHIE velocimetry of Kepler transit candidates V. The three hot Jupiters KOI-135b, KOI-204b, and KOI-203b (alias Kepler-17b)

We report the discovery of two new transiting hot Jupiters, KOI-135b and KOI-204b, which were previously identified as planetary candidates by the Kepler team, and independently confirm the planetary nature of Kepler-17b, recently announced by Desert et al. (2011, ApJS, 197, 14). Radial-velocity measurements, taken with the SOPHIE spectrograph at the Observatoire de Haute-Provence (France), and Kepler photometry (Q1 and Q2 data) were used to derive the orbital, stellar, and planetary parameters. KOI-135b and KOI-204b orbit their parent stars in similar to 3.02 and 3.25 days, respectively. They have approximately the same radius, R-p = 1.20 +/- 0.06 R-Jup and 1.24 +/- 0.07 R-Jup, but different masses M-p = 3.23 +/- 0.19 M-Jup and 1.02 +/- 0.07 M-Jup. As a consequence, their bulk densities differ by a factor of four, rho(p) = 2.33 +/- 0.36 g cm(-3) (KOI-135b) and 0.65 +/- 0.12 g cm(-3) (KOI-204b), meaning that their interior structures are different. All three planets orbit metal-rich stars with [Fe/H] similar to 0.3 dex. Our SOPHIE spectra of Kepler-17 were used both to measure the radial-velocity variations and to determine the stellar atmospheric parameters, allowing us to refine the characterisation of the planetary system. In particular we found the radial-velocity semi-amplitude and the stellar mass to be respectively slightly smaller and larger than in Desert et al. These two quantities, however, compensate and lead to a fully consistent planetary mass. Our analysis gives M-p = 2.47 +/- 0.10 M-Jup and R-p = 1.33 +/- 0.04 R-Jup. We found evidence of a younger age for this planetary system, t textless 1.8 Gyr, which is supported by both evolutionary tracks and gyrochronology. Finally, we confirm the detection of the optical secondary eclipse by Desert et al. and also find the brightness phase variation with the Q1 and Q2 Kepler data. The latter indicates a low redistribution of stellar heat to the night side (textless16% at 1-sigma), if the optical planetary occultation comes entirely from thermal flux. The geometric albedo is A(g) textless 0.12 (1-sigma).

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.

Transiting exoplanets from the CoRoT space mission XIII. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT’s observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing HIRES spectra from the Keck telescope. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter masses, 0.9 Jupiter radii, and a density of 2.34 g cm −3 . It orbits a G0V star with Teff = 5 945 K, M∗ = 1.09 M� , R∗ = 1.01 R� , solar metallicity, a lithium content of +1.45 dex, and an estimated age of between 0.12 and 3.15 Gyr. The lithium abundance of the star is consistent with its effective temperature, activity level, and age range derived from the stellar analysis. The density of the planet is extreme for its mass, implies that heavy elements are present with a mass of between about 140 and 300 M⊕.

Transiting exoplanets from the CoRoT space mission - XX. CoRoT-20b: A very high density, high eccentricity transiting giant planet

We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most compact planets known so far. Evolution models for the planet suggest a mass of heavy elements of the order of 800 ME if embedded in a central core, requiring a revision either of the planet formation models or of planet evolution and structure models. We note however that smaller amounts of heavy elements are expected from more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56. The stars projected rotational velocity is vsini = 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving towards a triple synchronous state with equality of the orbital, planetary and stellar spin periods.