# EPIC211682544b: A 50-day period sub-Neptune with a mass measurement using HARPS-N

A. Mortier, A. S. Bonomo, V. M. Rajpaul, L. A. Buchhave, A. Vanderburg, L. Zeng, M. López-Morales, L. Malavolta, A. Collier Cameron, C. D. Dressing, P. Figueira, V. Nascimbeni, K. Rice, A. Sozzetti, C. Watson, L. Affer, F. Bouchy, D. Charbonneau, A. Harutyunyan, R. D. HaywoodJ. A. Johnson, D. W. Latham, C. Lovis, A. F. Martinez Fiorenzano, M. Mayor, G. Micela, E. Molinari, F. Motalebi, F. Pepe, G. Piotto, D. Phillips, E. Poretti, D. Sasselov, D. Ségransan, S. Udry

Research output: Contribution to journalArticlepeer-review

## Abstract

This paper reports on the validation and mass measurement of EPIC211682544b, a sub-Neptune orbiting a quiet G9V star. Using K2 data from campaigns C5 and C16, we find this planet to have a period of$50.818947\pm 0.000094$ days and a radius of $2.41\pm0.12$ R$_{\oplus}$.We followed this system with HARPS-N to obtain 67 precise radial velocities. A combined fit of the transit and radial velocity data reveals that EPIC211682544b has a mass of $14.8\pm3.1$ M$_{\oplus}$. Its bulk density ($5.7_{-1.4}^{+1.6}$ g cm$^{-3}$) implies that this planet has a significant envelope of water or other volatiles around a rocky core. EPIC211682544b likely formed in a similar way as the cores of the four giant planets in our own Solar System, but for some reason, did not accrete much gas. The planetary mass was confirmed by an independent Gaussian process-based fit to both the radial velocities and the spectroscopic activity indicators. EPIC211682544b belongs to only a handful of confirmed K2 exoplanets with periods longer than 40 days. Itis among the longest periods for a small planet with a precisely determined mass using radial velocities.
Original language English 10 Monthly Notices of the Royal Astronomical Society 03 Sep 2018 Published - Dec 2018

## Keywords

• Astrophysics - Earth and Planetary Astrophysics

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