K2-139 b: a low-mass warm Jupiter on a 29-d orbit transiting an active K0 V star
Erikson, A.; Pätzold, M.; Rauer, H.; Eiroa, C.; Barragán, O.; Gandolfi, D.; Fossati, L.; Korth, J.; Prieto-Arranz, J.; Nespral, D.; Grziwa, S.; Hatzes, A. P.; Smith, A. M. S.; Cabrera, J.; Cochran, W. D.; Persson, C. M.; Cusano, F.; Deeg, H. J.; Mancini, L.; Csizmadia, Sz; Endl, M.; Guenther, E.; Zakhozhay, O. V.; Brems, S. S.; Rebollido, I.; Lorenzo-Oliveira, D.; Eigmüller, Ph; Donati, P.; Saario, J.; Fridlund, M. C. V.
Italy, Germany, Spain, Sweden, Netherlands, United States, Austria, Brazil, Ukraine
Abstract
We announce the discovery of K2-139 b (EPIC 218916923 b), a transiting warm-Jupiter (Teq = 547 ± 25 K) on a 29-d orbit around an active (log R^' _HK = -4.46 ± 0.06) K0 V star in K2 Campaign 7. We derive the system's parameters by combining the K2 photometry with ground-based follow-up observations. With a mass of 0.387 _{ - 0.075 } ^ {+ 0.083 }MJ and radius of 0.808 _{ - 0.033 } ^ {+ 0.034 }RJ, K2-139 b is one of the transiting warm Jupiters with the lowest mass known to date. The planetary mean density of 0.91 _{ - 0.20} ^ { + 0.24 } g cm-3can be explained with a core of ∼50 M⊕. Given the brightness of the host star (V = 11.653 mag), the relatively short transit duration (∼5 h), and the expected amplitude of the Rossiter-McLaughlin effect (∼25m s-1), K2-139 is an ideal target to measure the spin-orbit angle of a planetary system hosting a warm Jupiter.