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

H. P. Osborn, D. J. Armstrong, V. Zh. Adibekyan, K. A. Collins, E. Delgado Mena, S. B. Howell, C. Hellier, G. W. King, J. Lillo-Box, L. D. Nielsen, J. F. Otegi, N. C. Santos, C. Ziegler, D. R. Anderson, C. Briceño, C. Burke, D. Bayliss, D. Barrado, E. M. Bryant, D. J. A. Brown, S. C. C. Barros, F. Bouchy, D. A. Caldwell, D. M. Conti, R. F. Díaz, D. Dragomir, M. Deleuil, O. Demangeon, C. Dorn, T. Daylan, P. Figueira, R. Helled, S. Hoyer, J. M. Jenkins, E. L. N. Jensen, D. W. Latham, N. M. Law, D. R. Louie, A. W. Mann, A. Osborn, D. Pollacco, D. R. Rodriguez, B. V. Rackham, G. R. Ricker, N. J. Scott, S. G. Sousa, S. Seager, Stassun K. G., J. C. Smith, P. Strøm, S. Udry, J. Villaseñor, R. K. Vanderspek, R. D. West, P. J. Wheatley, J. N. Winn

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.

Keywords
planets and satellites: detection; stars: individual: HD110113; Astrophysics - Earth and Planetary Astrophysics

Monthly Notices of the Royal Astronomical Society
Volume 502, Issue 4, Page 4842
2021 April

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia