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

J. M. Almenara 1 F. Bouchy 2, 3 P. Gaulme 4 M. Deleuil 1 M. Havel 5 D. Gandolfi 6 H. J. Deeg 3 G. Wuchterl 7 T. Guillot 5 B. Gardes 8 T. Pasternacki S. Aigrain R. Alonso 9 M. Auvergne 10 A. Baglin 10 A. S. Bonomo P. Borde J. Cabrera 11 S. Carpano W. D. Cochran Sz. Csizmadia C. Damiani 12 R. F. Diaz R. Dvorak 13 M. Endl A. Erikson 14 S. Ferraz-Mello 15 M. Fridlund 16 G. Hébrard 3 M. Gillon 17, 18 E. Guenther A. Hatzes 7 A. Léger 19 H. Lammer 20 P. J. Macqueen T. Mazeh C. Moutou 1 M. Ollivier 21 A. Ofir M. Paetzold 22 H. Parviainen D. Queloz 17 H. Rauer 23 D. Rouan 10 A. Santerne 1 B. Samuel 10 J. Schneider 24 L. Tal-Or B. Tingley J. Weingrill 20 
Abstract : 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.
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J. M. Almenara, F. Bouchy, P. Gaulme, M. Deleuil, M. Havel, et al.. Transiting exoplanets from the CoRoT space mission: XXIV. CoRoT-25b and CoRoT-26b: two low-density giant planets. Astronomy and Astrophysics - A&A, 2013, 555, ⟨10.1051/0004-6361/201321462⟩. ⟨hal-01441496⟩

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