Vol. 562
In section 10. Planets and planetary systems

Kepler-91 b: a planet at the end of its life

by J. Lillo-Box, D. Barrado, A. Moya, et al., A&A 562, A109


KOI-2133 is a giant star observed by the Kepler spacecraft. It was identified as an "object of interest" because of transits compatible with a planet-size object on a 6.2-day orbit. However, a first study by Esteves et al. (ApJ 2013, 752, 51) concluded that the transiting object had to be self-luminous on the basis of the depth of its secondary eclipse so that it was probably a case of a false positive: an eclipsing binary mimicking a planetary transit because of dilution by another star. In this issue, Lillo-Box et al. very carefully examine the constraints that can be obtained on the parent star through its oscillations and derive a mass of 1.3 solar masses and a radius of 6.3 solar radii. These results are significantly different from what was derived previously. Solving for the orbital characteristics of the companion, they obtain a mass of 0.9 Jupiter masses for a radius of 1.38 Jupiter radii, a non-zero eccentricity of ~0.07, and an albedo smaller than 0.4 (i.e., the object is not self-luminous). These parameters are typical of the standard hot Jupiters known so far. Nevertheless, the planet is orbiting so close to its star that it comes a mere 1.3 stellar radii away from the stellar photosphere, which is a record! Future studies should shed light on the dynamical and thermal history of planets and on star-planet tidal interactions. Besides this, this soon-to-be engulfed planet now has a name: Kepler-91 b.