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.

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

[2]  Conny Aerts,et al.  Correcting for background changes in CoRoT exoplanet data , 2008 .

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

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

[5]  David Ehrenreich,et al.  Mass-loss rates for transiting exoplanets , 2011, 1103.0011.

[6]  R. L. Kurucz,et al.  New Grids of ATLAS9 Model Atmospheres , 2004, astro-ph/0405087.

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

[8]  C. Moutou,et al.  A transiting giant planet with a temperature between 250 K and 430 K , 2010, Nature.

[9]  Antonino Francesco Lanza,et al.  Detection of Neptune-size planetary candidates with CoRoT data. Comparison with the planet occurrence rate derived from Kepler , 2012, 1209.4815.

[10]  The N2K Consortium. II. A Transiting Hot Saturn around HD 149026 with a Large Dense Core , 2005, astro-ph/0507009.

[11]  C. Aerts,et al.  Jitter Correction Algorithms for the COROT Satellite Mission , 2006 .

[12]  P. Gregory.  A Bayesian Analysis of Extrasolar Planet Data for HD 73526 , 2005 .

[13]  Carnegie,et al.  HAT-P-1b: A Large-Radius, Low-Density Exoplanet Transiting One Member of a Stellar Binary* ** , 2007 .

[14]  D. Queloz,et al.  The CORALIE survey for southern extra-solar planets VII - Two short-period Saturnian companions to HD 108147 and HD 168746 , 2002, astro-ph/0202457.

[15]  T. Guillot,et al.  The multiple planets transiting Kepler-9 I. Inferring stellar properties and planetary compositions , 2011, 1103.6020.

[16]  Wm. A. Wheaton,et al.  2MASS All Sky Catalog of point sources. , 2003 .

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

[18]  C. Moutou,et al.  Radial velocity follow-up for confirmation and characterization of transiting exoplanets , 2007, Proceedings of the International Astronomical Union.

[19]  David Charbonneau,et al.  TrES-1: The Transiting Planet of a Bright K0 V Star , 2004 .

[20]  et al,et al.  Spin-orbit misalignment in the HD 80606 planetary system , 2009, 0906.5605.

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

[22]  R. Kurucz.  ATLAS9 Stellar Atmosphere Programs and 2 km/s grid. , 1993 .

[23]  C. Surace,et al.  EXO-DAT: AN INFORMATION SYSTEM IN SUPPORT OF THE CoRoT/EXOPLANET SCIENCE , 2009 .

[24]  A. Claret,et al.  A new non-linear limb-darkening law for LTE stellar atmosphere models III , 2000 .

[25]  H. J. Deeg,et al.  The CoRoT space mission : early results Special feature Ground-based photometry of space-based transit detections : photometric follow-up of the CoRoT mission , 2009 .

[26]  P. Gondoin,et al.  Transiting exoplanets from the CoRoT space mission - IX. CoRoT-6b: a transiting “hot Jupiter” planet in an 8.9d orbit around a low-metallicity star , 2010, 1001.1426.

[27]  Willy Benz,et al.  Extrasolar planet population synthesis - II. Statistical comparison with observations , 2009, 0904.2542.

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

[29]  Tel Aviv,et al.  Multi-order TODCOR: application to observations taken with the CORALIE echelle spectrograph I. The system HD 41004 ⋆,⋆⋆ , 2003 .

[30]  P. Gondoin,et al.  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 , 2010, 1009.2597.

[31]  G. L. Wycoff,et al.  THE THIRD US NAVAL OBSERVATORY CCD ASTROGRAPH CATALOG (UCAC3) , 2004, 1003.2136.

[32]  E. Agol,et al.  Analytic Light Curves for Planetary Transit Searches , 2002, astro-ph/0210099.

[33]  A. Erikson,et al.  The effect of stellar limb darkening values on the accuracy of the planet radii derived from photometric transit observations , 2012, 1212.2372.

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

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

[36]  M. Mayor,et al.  The Geneva–Copenhagen Survey of the Solar Neighbourhood , 2004, Publications of the Astronomical Society of Australia.

[37]  Tristan Guillot,et al.  Evolution of "51 Pegasus b-like" planets , 2002 .

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

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

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

[41]  Konstantin Batygin,et al.  EVOLUTION OF OHMICALLY HEATED HOT JUPITERS , 2011, 1101.3800.

[42]  R. G. West,et al.  WASP-4b: A 12th Magnitude Transiting Hot Jupiter in the Southern Hemisphere , 2008, 0801.1509.

[43]  Debra A. Fischer,et al.  The Exoplanet Orbit Database , 2010, 1012.5676.

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

[45]  Tel Aviv,et al.  An intriguing correlation between the masses and periods of the transiting planets , 2004, astro-ph/0411701.

[46]  Howard Isaacson,et al.  Kepler Planet-Detection Mission: Introduction and First Results , 2010, Science.

[47]  Tristan Guillot,et al.  An analysis of the CoRoT-2 system: A young spotted star and its inflated giant planet , 2010, 1010.1078.

[48]  R. Rebolo,et al.  Enhanced lithium depletion in Sun-like stars with orbiting planets , 2009, Nature.

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

[50]  L. Siess.  Evolution of massive AGB stars , 2006 .

[51]  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.

[52]  C. G. Tinney,et al.  Observed Properties of Exoplanets : Masses, Orbits, and Metallicities(Origins : From Early Universe to Extrasolar Planets) , 2005 .

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

[54]  C. Moutou,et al.  Transiting exoplanets from the CoRoT space mission. VII. The ``hot-Jupiter''-type planet CoRoT-5b , 2009 .

[55]  Josef Kallrath,et al.  Eclipsing Binary Stars: Modeling and Analysis , 1999 .

[56]  Ignasi Ribas,et al.  A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars , 2006, astro-ph/0605751.

[57]  Gregory Laughlin,et al.  ON THE ANOMALOUS RADII OF THE TRANSITING EXTRASOLAR PLANETS , 2011, 1101.5827.

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

[59]  L. Hillenbrand,et al.  Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics , 2008, 0807.1686.

[60]  David R. Alexander,et al.  The NEXTGEN Model Atmosphere Grid. II. Spherically Symmetric Model Atmospheres for Giant Stars with Effective Temperatures between 3000 and 6800 K , 1999, astro-ph/9907194.

[61]  L. Testi,et al.  The Star Formation in the L1615/L1616 Cometary Cloud , 2008, 0807.0532.

[62]  Juri Toomre,et al.  SOHO 18/GONG 2006/HELAS I Beyond the spherical Sun , 2006 .

[63]  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 .

[64]  Antonino Francesco Lanza,et al.  Transiting exoplanets from the CoRoT space mission - X. CoRoT-10b: a giant planet in a 13.24 day eccentric orbit , 2010, 1006.2949.

[65]  C. Moutou,et al.  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 , 2010, 1007.5481.

[66]  S. Barnes.  Accepted for publication in The Astrophysical Journal Ages for illustrative field stars using gyrochronology: viability, limitations and errors , 2022 .

[67]  T. Sakurai,et al.  Behavior of Li abundances in solar-analog stars - Evidence for line-width dependence , 2007 .

[68]  Observatoire de Geneve,et al.  VLT transit and occultation photometry for the bloated planet CoRoT-1b , 2009, 0905.4571.

[69]  A. D. Etangs,et al.  A diagram to determine the evaporation status of extrasolar planets , 2006, astro-ph/0609744.

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

[71]  Jonathan J. Fortney,et al.  THE HEAVY-ELEMENT MASSES OF EXTRASOLAR GIANT PLANETS, REVEALED , 2011, 1105.0024.

[72]  Michel Mayor,et al.  ELODIE: A spectrograph for accurate radial velocity measurements , 1996 .

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

[74]  Subrahmanyan Chandrasekhar,et al.  Ellipsoidal Figures of Equilibrium , 1969 .

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