HAT-P-54b: A Hot Jupiter Transiting a 0.6 M⊙ Star in Field 0 of the K2 Mission

We report the discovery of HAT-P-54b, a planet transiting a late K dwarf star in field 0 of the NASA K2 mission. We combine ground-based photometric light curves with radial velocity measurements to determine the physical parameters of the system. HAT-P-54b has a mass of 0.760\+/- 0.032 {{M}_J}, a radius of 0.944 ± 0.028 {{R}_J}, and an orbital period of 3.7998 days. The star has V=13.505\+/- 0.060, a mass of 0.645\+/- 0.020 {{M}}, a radius of 0.617\+/- 0.013 {{R}}, an effective temperature of {{T}_eff\star }=4390\+/- 50, and a subsolar metallicity of [Fe/H]=-0.127\+/- 0.080. We also detect a periodic signal with P = 15.6 days and 5.6 mmag amplitude in the light curve, which we interpret as due to the rotation of the star. HAT-P-54b has a radius that is smaller than 92% of the known transiting planets with masses greater than that of Saturn, while HAT-P-54 is one of the lowest-mass stars known to host a hot Jupiter. Follow-up high-precision photometric observations by the K2 mission promise to make this a well-studied planetary system.

Based on observations obtained with the Hungarian-made Automated Telescope Network (HATNet). Based in part on observations obtained at the W. M. Keck Observatory, using time granted by NASA (N133Hr). Based in part on observations obtained with the Tillinghast Reflector 1.5 m telescope and the 1.2 m telescope, both operated by the Smithsonian Astrophysical Observatory at the Fred Lawrence Whipple Observatory in Arizona.