Structure and evolution of the first CoRoT exoplanets: Probing the Brown Dwarf/Planet overlapping mass regime

TL;DR

This paper analyzes the structure and evolution of the first CoRoT exoplanets, distinguishing different categories including planets, bloated planets, and brown dwarf/planet overlap objects, with implications for their internal composition and classification.

Contribution

It provides detailed models for CoRoT exoplanets, discusses tidal heating effects, and explores the nature of CoRoT-3b, advancing understanding of substellar object classification.

Findings

Tidal heating explains bloated planets with non-zero eccentricities.

Radius measurements align with theoretical predictions for substellar bodies.

Identification of brown dwarfs and giant planets in overlapping mass ranges.

Abstract

We present detailed structure and evolution calculations for the first transiting extrasolar planets discovered by the space-based CoRoT mission. Comparisons between theoretical and observed radii provide information on the internal composition of the CoRoT objects. We distinguish three different categories of planets emerging from these discoveries and from previous ground-based surveys: (i) planets explained by standard planetary models including irradiation, (ii) abnormally bloated planets and (iii) massive objects belonging to the overlapping mass regime between planets and brown dwarfs. For the second category, we show that tidal heating can explain the relevant CoRoT objects, providing non-zero eccentricities. We stress that the usual assumption of a quick circularization of the orbit by tides, as usually done in transit light curve analysis, is not justified a priori, as suggested recently by Levrard et al. (2009), and that eccentricity analysis should be carefully redone for some observations. Finally, special attention is devoted to CoRoT-3b and to the identification of its very nature: giant planet or brown dwarf ? The radius determination of this object confirms the theoretical mass-radius predictions for gaseous bodies in the substellar regime but, given the present observational uncertainties, does not allow an unambiguous identification of its very nature. This opens the avenue, however, to an observational identification of these two distinct astrophysical populations, brown dwarfs and giant planets, in their overlapping mass range, as done for the case of the 8 Jupiter-mass object Hat-P-2b. (abridged)