HATS-2b: A transiting extrasolar planet orbiting a K-type star showing starspot activity

Abstract

We report the discovery of HATS-2b, the second transiting extrasolar planet detected by the HATSouth survey. HATS-2b is moving on a circular orbit around a V = 13 . 6 mag, K -type dwarf star (GSC 6665-00236), at a separation of 0 . 0230 ± 0 . 0003 AU and with a period of 1 . 3541 days. The planetary parameters have been robustly determined using a simultaneous fit of the HATSouth, MPG / ESO 2.2 m / GROND, Faulkes Telescope South / Spectral transit photometry, and MPG / ESO 2.2 m / FEROS, Euler 1.2 m / CORALIE, AAT 3.9 m / CYCLOPS radial-velocity measurements. HATS-2b has a mass of 1 . 37 ± 0 . 16 M J , a radius of 1 . 14 ± 0 . 03 R J , and an equilibrium temperature of 1567 ± 30 K. The host star has a mass of 0 . 88 ± 0 . 04 M and a radius of 0 . 89 ± 0 . 02 R , and it shows starspot activity. We characterized the stellar activity by analyzing two photometric follow-up transit light curves taken with the GROND instrument, both obtained simultaneously in four optical bands (covering the wavelength range of 3860 − 9520 Å). The two light curves contain anomalies compatible with starspots on the photosphere of the host star along the same transit chord.