Transiting exoplanets from the CoRoT space mission . VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert

Context. The CoRoT  space mission routinely provides high-precision photometric measurements of thousands of stars that have been continuously observed for months. Aims. The discovery and characterization of the first very massive transiting planetary companion with a short orbital period is reported. Methods. A series of 34 transits was detected in the CoRoT  light curve of an F3V star, observed from May to October 2007 for 152 days. The radius was accurately determined and the mass derived for this new transiting, thanks to the combined analysis of the light curve and complementary ground-based observations: high-precision radial-velocity measurements, on-off photometry, and high signal-to-noise spectroscopic observations. Results. CoRoT-Exo-3b  has a radius of 1.01 ± 0.07  R Jup  and transits around its F3-type primary every 4.26 days in a synchronous orbit. Its mass of 21.66 ± 1.0  M Jup , density of 26.4 ± 5.6 g cm -3 , and surface gravity of log g = 4.72 clearly distinguish it from the regular close-in planet population, making it the most intriguing transiting substellar object discovered so far. Conclusions. With the current data, the nature of CoRoT-Exo-3b is ambiguous, as it could either be a low-mass brown-dwarf or a member of a new class of “superplanets”. Its discovery may help constrain the evolution of close-in planets and brown-dwarfs better. Finally, CoRoT-Exo-3b confirms the trend that massive transiting giant planets ( M ≥ 4 M Jup ) are found preferentially around more massive stars than the Sun.

[1]  D. Schlegel,et al.  Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds , 1997, astro-ph/9710327.

[2]  Á. Giménez.  Equations for the analysis of the light curves of extra-solar planetary transits , 2006 .

[3]  Nuno C. Santos,et al.  Extrasolar Planets: Statistical properties of exoplanets , 2007 .

[4]  Michel Mayor,et al.  Multi-order TODCOR: Application to observations taken with the CORALIE echelle spectrograph - II. A planet in the system HD 41004 , 2004 .

[5]  Richard Greenberg,et al.  Tidal Heating of Extrasolar Planets , 2008, 0803.0026.

[6]  I. Baraffe,et al.  Structure and evolution of super-Earth to super-Jupiter exoplanets - I. Heavy element enrichment in the interior , 2008, 0802.1810.

[7]  Willy Benz,et al.  Models of giant planet formation with migration and disc evolution , 2004 .

[8]  A. Claret,et al.  A new non-linear limb-darkening law for LTE stellar atmosphere models III - Sloan filters: Calculations for –5.0 ≤ log [M/H] ≤ +1, 2000 K ≤ T$\mathsf{_{eff}}$ ≤ 50 000 K at several surface gravities , 2004 .

[9]  Peter R. McCullough,et al.  XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5 V Star , 2007, 0712.4283.

[10]  S. Baliunas,et al.  No Planet for Hd 166435 , 2022 .

[11]  D. Queloz,et al.  HAT-P-5b: A Jupiter-like Hot Jupiter Transiting a Bright Star , 2007, 0710.1841.

[12]  Charles H. Lineweaver,et al.  How Dry is the Brown Dwarf Desert? Quantifying the Relative Number of Planets, Brown Dwarfs, and Stellar Companions around Nearby Sun-like Stars , 2004 .

[13]  C. Moutou,et al.  Transiting exoplanets from the CoRoT space mission , 2008, Astronomy & Astrophysics.

[14]  John Southworth,et al.  Homogeneous studies of transiting extrasolar planets – I. Light-curve analyses , 2008, 0802.3764.

[15]  J. Valenti,et al.  Spectroscopy Made Easy: A New Tool for Fitting Observations with Synthetic Spectra , 1996 .

[16]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .

[17]  D. Queloz,et al.  The CORALIE survey for southern extra-solar planets - VIII. The very low-mass companions of HD 141937, HD 162020, HD 168443 and HD 202206: Brown dwarfs or “superplanets”? , 2002 .

[18]  C. Aerts,et al.  A spectroscopic study of southern (candidate) gamma Doradus stars. II. Detailed abundance analysis and fundamental parameters , 2007, 0711.3819.

[19]  D. Queloz,et al.  Extrasolar planets and brown dwarfs around A-F type stars. I. Performances of radial velocity measurements, first analyses of variations , 2005 .

[20]  C. Moutou,et al.  Transiting exoplanets from the CoRoT space mission: III. The spectroscopic transit of CoRoT-Exo-2b with SOPHIE and HARPS , 2008, 0803.3209.

[21]  David Charbonneau,et al.  Using Stellar Limb-Darkening to Refine the Properties of HD 209458b , 2006, astro-ph/0603542.

[22]  J. Hearnshaw,et al.  A search for substellar companions to southern solar-type stars , 1993 .

[23]  P. H. Hauschildt,et al.  Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458 , 2003 .

[24]  Lionel Siess,et al.  Evolution of massive AGB stars: I.Carbon burning phase , 2006 .

[25]  A. Collier Cameron,et al.  Transiting exoplanets from the CoRoT space mission. IV. CoRoT-Exo-4b: a transiting planet in a 9.2 d , 2008, 0807.3767.

[26]  G. Rieke,et al.  The interstellar extinction law from 1 to 13 microns. , 1985 .

[27]  David Charbonneau,et al.  Hubble Space Telescope Time-Series Photometry of the Transiting Planet of HD?209458 , 2001 .

[28]  C. Moutou,et al.  Transiting exoplanets from the CoRoT space mission - II. CoRoT-Exo-2b: a transiting planet around an active G star , 2008, 0803.3207.

[29]  G. Rolland,et al.  Radiation effects on space-based stellar photometry: theoretical models and empirical results for CoRoT Space Telescope , 2008 .

[30]  C. Moutou,et al.  Magnetic cycles of the planet-hosting star τ Bootis , 2008, 0802.1584.

[31]  D. Lin,et al.  Spin-Orbit Evolution of Short-Period Planets , 2004, astro-ph/0408191.