HD 183579b: A Warm Sub-Neptune Transiting a Solar Twin Detected by TESS

Abstract

We report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright ($V=8.75$ mag, $K=7.15$ mag) solar twin HD 183579, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located $56.8\pm 0.1$ pc away with a radius of $R_{\ast }=0.97\pm 0.02R_{\odot }$ and a mass of $M_{\ast }=1.03\pm 0.05M_{\odot }$. We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of $R_p=3.53\pm 0.13R_{\oplus }$ on a $17.47$ day orbit with a mass of $M_p=11.2\pm 5.4M_{\oplus }$ ($3\ddot{I}ƒ$ mass upper limit of $27.4M_{\oplus }$). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion.

20 pages, 15 figures, accepted for publication in MNRAS