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

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 (𝑇 eff = 5730K). Using TESS photometry and HARPS radial velocities gathered by the NCORES program, we find 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 onto a substantial (0.1-1%) H-He atmosphere over its ∼ 4Gyr 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 with a mass of 10.5 ± 1.2 M ⊕ and a period of 6.744 +0.008 −0.009 d.