Mon. Not. R. Astron. Soc., 470, 932-939 (2017/September-1)
Rapid rotators revisited: absolute dimensions of KOI-13.
HOWARTH I.D. and MORELLO G.
Abstract (from CDS):
We analyse Kepler light-curves of the exoplanet Kepler Object of Interest no. 13b (KOI-13b) transiting its moderately rapidly rotating (gravity-darkened) parent star. A physical model, with minimal ad hoc free parameters, reproduces the time-averaged light-curve at the ∼10 parts per million level. We demonstrate that this Roche-model solution allows the absolute dimensions of the system to be determined from the star's projected equatorial rotation speed, ve sin i*, without any additional assumptions; we find a planetary radius RP = (1.33 ± 0.05) R, stellar polar radius Rp = (1.55 ± 0.06) R☉, combined mass M* + MP( ≃ M*) = (1.47 ± 0.17) M☉ and distance d ≃ (370 ± 25) pc, where the errors are dominated by uncertainties in relative flux contribution of the visual-binary companion KOI-13B. The implied stellar rotation period is within ∼5 per cent of the non-orbital, 25.43-hr signal found in the Kepler photometry. We show that the model accurately reproduces independent tomographic observations, and yields an offset between orbital and stellar-rotation angular-momentum vectors of 60.○25 ± 0.○05.