A hot mini-Neptune in the radius valley orbiting solar analogue HD 110113

TL;DR

This paper reports the discovery and characterization of a mini-Neptune exoplanet orbiting a solar-analogue star, revealing its atmospheric composition, mass, radius, and the presence of an additional non-transiting planet.

Contribution

It presents the first detailed analysis of HD 110113 b, including its volatile atmosphere and the detection of a second non-transiting planet using combined photometry and radial velocity data.

Findings

HD 110113 b has a radius of 2.05 R_⊕ and a mass of 4.55 M_⊕.

The planet retains a 0.1-1% H-He atmosphere after 4 Gyr.

An additional non-transiting planet with 10.5 M_⊕ was confirmed.

Abstract

We report the discovery of HD 110113 b (TOI-755.01), a transiting mini-Neptune exoplanet on a 2.5-day orbit around the solar-analogue HD 110113 (Teff = 5730K). Using TESS photometry and HARPS radial velocities gathered by the NCORES program, we find HD 110113 b has a radius of $2.05\pm0.12$ $R_\oplus$ and a mass of $4.55\pm0.62$ $M_\oplus$. The resulting density of $2.90^{+0.75}_{-0.59}$ g cm^{-3} is significantly lower than would be expected from a pure-rock world; therefore, HD 110113 b must be a mini-Neptune with a significant volatile atmosphere. The high incident flux places it within the so-called radius valley; however, HD 110113 b was able to hold onto a substantial (0.1-1\%) H-He atmosphere over its $\sim4$ Gyr lifetime. Through a novel simultaneous gaussian process fit to multiple activity indicators, we were also able to fit for the strong stellar rotation signal with period $20.8\pm1.2$ d from the RVs and confirm an additional non-transiting planet with a mass of $10.5\pm1.2$ $M_\oplus$ and a period of $6.744^{+0.008}_{-0.009}$ d.