The discovery and mass measurement of a new ultra-short-period planet: EPIC~228732031b

The discovery and mass measurement of a new ultra-short-period planet: EPIC~228732031b

Authors:

Dai et al

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, EPIC~228732031b, was discovered in {\it K2} Campaign 10. It has a radius of 1.81+0.16−0.12 R⊕ and orbits a G dwarf with a period of 8.9 hours. 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 6.5±1.6 M⊕, and a mean density of 6.0+3.0−2.7~g~cm−3.