Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here we present the characterization of a new mini-Neptune planet orbiting the bright (V=9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from Sectors 2, 3, 29, and 30, with an orbital period of 4.138~days. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.5±4.6~M⊕. When we combine this with the measured radius from TESS, of 2.70±0.05~R⊕, we find a high planetary density of 7.1±1.4~g cm−3. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23% H2O and 77% Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy.
@article{arxiv.2210.07945,
title = {A dense mini-Neptune orbiting the bright young star HD 18599},
author = {Jose I. Vines and James S. Jenkins and Zaira Berdiñas and Maritza G. Soto and Matías R. Díaz and Douglas R. Alves and Mikko Tuomi and Robert A. Wittenmyer and Jerome Pitogo de Leon and Pablo Peña and Jack J. Lissauer and Sarah Ballard and Timothy Bedding and Brendan P. Bowler and Jonathan Horner and Hugh R. A. Jones and Stephen R. Kane and John Kielkopf and Peter Plavchan and Avi Shporer and C. G. Tinney and Hui Zhang Duncan J. Wright and Brett Addison and Matthew W. Mengel and Jack Okumura and Anya Samadi-Ghadim},
journal= {arXiv preprint arXiv:2210.07945},
year = {2022}
}