Transiting Exoplanets From The CoRoT Space Mission XXIV. CoRoT-25b and CoRoT-26b: two low-density giant planets

Date

2013-07

Authors

Almenara, J. M.
Bouchy, F.
Gaulme, P.
Deleuil, M.
Havel, M.
Gandolfi, D.
Deeg, H. J.
Wuchterl, G.
Guillot, T.
Gardes, B.

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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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Citation

Almenara, J. M., F. Bouchy, P. Gaulme, M. Deleuil, M. Havel, D. Gandolfi, H. J. Deeg et al. >Transiting exoplanets from the CoRoT space mission-XXIV. CoRoT-25b and CoRoT-26b: two low-density giant planets.> Astronomy & Astrophysics, Vol. 555 (Jul., 2013): A118.