HAT-P-54b: A hot jupiter transiting a 0.64 Msun star in field 0 of the K2 mission

Abstract

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 \(\pm\) 0.032 \(M_J\), a radius of 0.944 \(\pm\) 0.028 \(R_J\), and an orbital period of 3.7998 d. The star has V = 13.505 \(\pm\) 0.060, a mass of 0.645 \(\pm\) 0.020 \(M_{\odot}\), a radius of 0.617 \(\pm\) 0.013 \(R_{\odot}\), an effective temperature of Teff = 4390 \(\pm\) 50K, and a subsolar metallicity of [Fe/H] = -0.127 \(\pm\) 0.080. 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.