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

Abstract

We report the discovery of HD?110113?b (TESS object of interest-755.01), a transiting mini-Neptune exoplanet on a 2.5-d orbit around the solar-analogue HD?110113 (Teff = 5730 K). Using TESS photometry and High Accuracy Radial velocity Planet Searcher (HARPS) radial velocities gathered by the NCORES program, we find that HD?110113?b has a radius of 2.05 ± 0.12 ?R? and a mass of 4.55 ± 0.62 ?M?. 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 on to a substantial (0.1–1 per cent) H–He atmosphere over its ~4 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 ± 1.2 ?d from the RVs and confirm an additional non-transiting planet, HD 110113 c, which has a mass of 10.5 ± 1.2 ?M? and a period of 6.744+0.008-0.009 ?d.