The clockwork is moving on - a combined analysis of TESS and Kepler measurements of Kepler-13Ab

Szabó, Gy. M. and Pribulla, T. and Pál, A. and Bódi, A. and Kiss, L.L. and Derekas, A. (2020) The clockwork is moving on - a combined analysis of TESS and Kepler measurements of Kepler-13Ab. Monthly Notices of the Royal Astronomical Society, 492 (1). L17-L21.

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Abstract

Kepler-13Ab (KOI-13) is an exoplanet orbiting a rapidly rotating A-type star. The system shows a significant spin-orbit misalignment and a changing transit duration most probably caused by the precession of the orbit. Here, we present a self-consistent analysis of the system combining Kepler and Transiting Exoplanet Survey Satellite (TESS) observations. We model the light curves assuming a planet transits a rotating oblate star that has a strong surface temperature gradient due to rotation-induced gravity darkening. The transit chord moves slowly as an emergent feature of orbital precession excited by the oblate star with a decline rate in the impact parameter of db/dt = -0.011 yr-1, and with an actual value of b = 0.19 for the latest TESS measurements. The changing transit duration that was measured from Kepler Q2 and Q17 quarters and the TESS measurements indicates a linear drift of the impact parameter. The solutions for the stellar spin axis suggest a nearly orthogonal aspect, with inclination around 100°.

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