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. HA
T-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.
We summarize the contribution of the HATNet project to extrasolar planet science, highlighting published planets (HAT-P-1b through HAT-P-26b). We also briefly discuss the operations, data analysis, candidate selection and confirmation procedures, and
we summarize what HATNet provides to the exoplanet community with each discovery.
