EPIC 246851721 b: A Tropical Jupiter Transiting a Rapidly Rotating Star in a Well-aligned Orbit

December 2018 • 2018AJ....156..250Y

Authors • Yu, Liang • Zhou, George • Rodriguez, Joseph E. • Huang, Chelsea X. • Vanderburg, Andrew • Quinn, Samuel N. • Gaudi, B. Scott • Beichman, Charles A. • Berlind, Perry • Bieryla, Allyson • Calkins, Michael L. • Ciardi, David R. • Crossfield, Ian J. M. • Eastman, Jason D. • Esquerdo, Gilbert A. • Latham, David W. • Stassun, Keivan G. • Villanueva, Steven, Jr.

Abstract • We report the discovery of EPIC 246851721 b, a “tropical” Jupiter in a 6.18-day orbit around the bright (V = 11.439) star EPIC 246851721 (TYC 1283-739-1). We present a detailed analysis of the system using K2 and ground-based photometry, radial velocities, Doppler tomography, and adaptive optics imaging. From our global models, we infer that the host star is a rapidly rotating (v\sin {I}\star = 74.92 {km} {{{s}}}-1) F dwarf with {T}eff} = 6202 K, {R}\star =1.586 {R} and {M}\star =1.317 {M}. EPIC 246851721 b has a radius of 1.051 ± 0.044 {\text{}}{R}{{J}}, and a mass of 3.0{}-1.2+1.1 {\text{}}{M}{{J}}. Doppler tomography reveals an aligned spin-orbit geometry, with a projected obliquity of -1\buildrel{\circ}\over{.} {47} -0.86+0.87, making EPIC 246851721 the fourth hottest star to host a Jovian planet with P > 5 days and a known obliquity. Using quasi-periodic signatures in its light curve that appear to be spot modulations, we estimate the star’s rotation period, and thereby infer the true obliquity of the system to be 3\buildrel{\circ}\over{.} {7} -1.8+3.7. We argue that this near-zero obliquity is likely to be primordial rather than a result of tidal damping. The host star also has a bound stellar companion, a 0.4 {M} M dwarf at a projected separation of 2100 au, but the companion is likely incapable of emplacing EPIC 246851721 b in its current orbit via high-eccentricity Kozai-Lidov migration.


IPAC Authors


David Ciardi

Senior Scientist