[en] 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 ± 0.04 M[SUB]Jup[/SUB], a radius of 1.08[SUB]-0.10[/SUB][SUP]+0.3[/SUP] R[SUB]Jup[/SUB] and hence a mean density of 0.15[SUB]-0.06[/SUB][SUP]+0.15[/SUP] g cm[SUP]-3[/SUP]. The planet orbits an F9 main-sequence star in a 4.86-day period, that has a V magnitude of 15.0, solar metallicity, and an age of 4.5[SUB]-2.0[/SUB][SUP]+1.8[/SUP]-Gyr. CoRoT-26b orbits a slightly evolved G5 star of 9.06 ± 1.5-Gyr age in a 4.20-day period that hassolar metallicity and a V magnitude of 15.8. With a mass of 0.52 ± 0.05 M[SUB]Jup[/SUB], a radius of 1.26[SUB]-0.07[/SUB][SUP]+0.13[/SUP] R[SUB]Jup[/SUB], and a mean density of 0.28[SUB]-0.07[/SUB][SUP]+0.09[/SUP] g cm[SUP]-3[/SUP], 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[SUB]-0.15[/SUB][SUP]+0.08[/SUP] and 0.26[SUB]-0.08[/SUB][SUP]+0.05[/SUP], 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. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Partly based on observations obtained at the European Southern Observatory at Paranal and La Silla, Chile in programs 083.C-0690(A), 184.C-0639.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Almenara, J. M.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
Bouchy, F.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France ; Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014, Paris, France
Gaulme, P.; Department of Astronomy, New Mexico State University, PO Box 30001, MSC 4500, Las Cruces, NM, 88003-8001, USA
Deleuil, M.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
Havel, M.; NASA Postdoctoral Program Fellow, Ames Research Center, PO Box 1, Moffett Field, CA, 94035, USA
Gandolfi, D.; Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG, Noordwijk, The Netherlands
Deeg, H. J.; Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain ; Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain
Guillot, T.; Observatoire de la Côte d'Azur, Laboratoire Cassiopée, BP 4229, 06304, Nice Cedex 4, France
Gardes, B.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
Pasternacki, T.; Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany
Aigrain, S.; Department of Physics, Denys Wilkinson Building Keble Road, Oxford, OX1 3RH, UK
Alonso, R.; Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain ; Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain ; Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290, Sauverny, Switzerland
Auvergne, M.; LESIA, Obs de Paris, Place J. Janssen, 92195, Meudon Cedex, France
Baglin, A.; LESIA, Obs de Paris, Place J. Janssen, 92195, Meudon Cedex, France
Bonomo, A. S.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France ; INAF - Osservatorio Astronomico di Torino, via Osservatorio 20, 10025, Pino Torinese, Italy
Bordé, P.; Institut d'astrophysique spatiale, Université Paris-Sud 11 & CNRS, UMR 8617, Bât. 121, 91405, Orsay, France
Cabrera, J.; Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany
Carpano, S.; Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG, Noordwijk, The Netherlands
Cochran, W. D.; McDonald Observatory, The University of Texas at Austin, Austin, TX, 78712, USA
Csizmadia, Sz; Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany
Damiani, C.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
Diaz, R. F.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
Dvorak, R.; University of Vienna, Institute of Astronomy, Türkenschanzstr. 17, 1180, Vienna, Austria
Endl, M.; McDonald Observatory, The University of Texas at Austin, Austin, TX, 78712, USA
Erikson, A.; Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany
Ferraz-Mello, S.; IAG, Universidade de Sao Paulo, Brazil
Fridlund, M.; Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG, Noordwijk, The Netherlands
Hébrard, G.; Observatoire de Haute Provence, 04670 Saint Michel l', Observatoire, France ; Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014, Paris, France
Gillon, Michaël ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Pätzold, M.; Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931, Köln, Germany
Parviainen, H.; Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain ; Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain
Queloz, D.; Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290, Sauverny, Switzerland
Rauer, H.; Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489, Berlin, Germany ; Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623, Berlin, Germany
Rouan, D.; LESIA, Obs de Paris, Place J. Janssen, 92195, Meudon Cedex, France
Santerne, A.; Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
Samuel, B.; LESIA, Obs de Paris, Place J. Janssen, 92195, Meudon Cedex, France
Schneider, J.; LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195, Meudon, France
Tal-Or, L.; Wise Observatory, Tel Aviv University, 69978, Tel Aviv, Israel
Tingley, B.; Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain ; Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain ; Department of Physics and Astronomy, Aarhus University, 8000, Aarhus C, Denmark
Weingrill, J.; Space Research Institute, Austrian Academy of Science, Schmiedlstr. 6, 8042, Graz, Austria)