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

Fei Dai , Joshua N. Winn , Davide Gandolfi , Sharon X. Wang , Johanna K. Teske , Jennifer Burt , Simon Albrecht , Oscar Barrag\'an

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William D. Cochran Michael Endl Malcolm Fridlund Artie P. Hatzes Teruyuki Hirano Lea A. Hirsch Marshall C. Johnson Anders Bo Justesen John Livingston Carina M. Persson Jorge Prieto-Arranz Andrew Vanderburg Roi Alonso Giuliano Antoniciello Pamela Arriagada R.P. Butler Juan Cabrera Jeffrey D. Crane Felice Cusano Szil\'ard Csizmadia Hans Deeg Sergio B. Dieterich Philipp Eigm\"uller Anders Erikson Mark E. Everett Akihiko Fukui Sascha Grziwa Eike W. Guenther Gregory W. Henry Steve B. Howell John Asher Johnson Judith Korth Masayuki Kuzuhara Norio Narita David Nespral Grzegorz Nowak Enric Palle Martin P\"atzold Heike Rauer Pilar Monta\~N\'Es Rodr\'Iguez Stephen A. Shectman Alexis M.S. Smith Ian B. Thompson Vincent Van Eylen Michael W. Williamson Robert A. Wittenmyer

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classification 🌌 astro-ph.EP

keywords massplanetdiscoveryepicmeasurementoplusradiusultra-short-period

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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$^{+0.16}_{-0.12}~R_{\oplus}$ 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 $6.5 \pm 1.6~M_{\oplus}$, and a mean density of $6.0^{+3.0}_{-2.7}$~g~cm$^{-3}$.

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

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