2013A&A...555A.118A

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±0.04M_Jup, a radius of 1.08^+0.3_–0.10R_Jup and hence a mean density of 0.15^+0.15_–0.06g/cm3. 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^+1.8_–2.0-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 ±0.05M_Jup, a radius of 1.26^+0.13_–0.07R_Jup, and a mean density of 0.28^+0.09_–0.07g/cm3, 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.