The Discovery and Mass Measurement of a New Ultra-short-period Planet: K2-131b

Abstract

We report the discovery of a new ultra-short-period planet and summarize the properties of all such planets for which the mass and radius have been measured. The new planet, K2-131b, was discovered in K2 Campaign 10. It has a radius of and orbits a G dwarf with a period of 8.9 hr. Radial velocities obtained with Magellan /PFS and TNG/HARPS-N show evidence for stellar activity along with orbital motion. We determined the planetary mass using two different methods: (1) the “floating chunk offset” method, based only on changes in velocity observed on the same night; and (2) a Gaussian process regression based on both the radial velocity and photometric time series. The results are consistent and lead to a mass measurement of and a mean density of g cm −3 .