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

J. M. ALMENARA; F. BOUCHY; P. GAULME; M. DELEUIL; M. HAVEL; D. GANDOLFI; H. J. DEEG; G. WUCHTERL; T. GUILLOT; B. GARDES; T. PASTERNACKI; S. AIGRAIN; R. ALONSO; M. AUVERGNE; A. BAGLIN; A. S. BONOMO; P. BORDÉ; J. CABRERA; S. CARPANO; W. D. COCHRAN; SZ. CSIZMADIA; C. DAMIANI; R. F. DÍAZ; AND 27 COAUTHORS

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2013 vol. 555 p. 1 - 11

0004-6361

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 MJup, a radius of 1.08-0.10+0.3 RJup and hence a mean density of 0.15-0.06+0.15 g cm-3. 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 4.5-2.0+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 hassolar 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 RJup, 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.