ajThe Astronomical JournalAJAstron. J.0004-62561538-3881The American Astronomical Societyajac314110.3847/1538-3881/ac3141ac3141AAS33963350The Solar System, Exoplanets, and AstrobiologyK2-79b and K2-222b: Mass Measurements of Two Small Exoplanets with Periods beyond 10 days that Overlap with Periodic Magnetic Activity Signals0000-0001-8838-3883NavaChantanelle1chantanelle.nava@cfa.harvard.edu0000-0003-3204-8183López-MoralesMercedes10000-0001-7254-4363MortierAnnelies230000-0003-1957-6635ZengLi140000-0001-6777-4797GilesHelen A. C.50000-0001-6637-5401BierylaAllyson10000-0001-7246-5438VanderburgAndrew60000-0003-1605-5666BuchhaveLars A.70000-0003-1200-0473PorettiEnnio890000-0001-7032-8480SaarSteven H.10000-0002-9332-2011DumusqueXavier50000-0001-9911-7388LathamDavid W.10000-0002-9003-484XCharbonneauDavid10000-0001-9984-4278DamassoMario100000-0002-6177-198XBonomoAldo S.10LovisChristophe5Collier CameronAndrew110000-0003-3773-5142EastmanJason D.10000-0002-7504-365XSozzettiAlessandro10CosentinoRosario80000-0002-5752-6260PedaniMarco8PepeFrancesco50000-0002-1742-7735MolinariEmilio120000-0001-7014-1771SasselovDimitar10000-0002-9352-5935MayorMichel5StalportManu50000-0002-6492-2085MalavoltaLuca1314RiceKen1516WatsonChristopher A.170000-0002-4272-4272Martinez FiorenzanoA. F.8Di FabrizioLuca8 Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA Astrophysics Group, Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, CH-1290 Sauverny, Switzerland Department of Astronomy, University of Wisconsin—Madison, WI 53706, USA DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 328, DK-2800 Kgs. Lyngby, Denmark Fundación Galileo Galilei-INAF, Rambla J. A. F. Perez, 7, E-38712, S.C. Tenerife, Spain INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate (LC), Italy INAF—Osservatorio Astrofisico di Torino, Via Osservaorio 20, I-10025 Pino Torinese, Italy Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK INAF—Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047, Selargius, Italy INAFOsservatorio Astronomico di Padova, Vicolo del l’Osservatorio 5, I-35122 Padova, Italy Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universitá di Padova, Vicolo del l’Osservatorio 3, I-35122 Padova, Italy SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK Centre for Exoplanet Science, University of Edinburgh, Edinburgh EH9 3FD, UK Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK 2202204012022040120221632417820212492021810202107082021© 2022. The Author(s). Published by the American Astronomical Society.2022 Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Abstract

We present mass and radius measurements of K2-79b and K2-222b, two transiting exoplanets orbiting active G-type stars observed with HARPS-N and K2. Their respective 10.99 day and 15.39 day orbital periods fall near periods of signals induced by stellar magnetic activity. The two signals might therefore interfere and lead to an inaccurate estimate of exoplanet mass. We present a method to mitigate these effects when radial velocity (RV) and activity-indicator observations are available over multiple observing seasons and the orbital period of the exoplanet is known. We perform correlation and periodogram analyses on subsets composed of each target's two observing seasons, in addition to the full data sets. For both targets, these analyses reveal an optimal season with little to no interference at the orbital period of the known exoplanet. We make a confident mass detection of each exoplanet by confirming agreement between fits to the full RV set and the optimal season. For K2-79b, we measure a mass of 11.8 ± 3.6 M and a radius of 4.09 ± 0.17 R . For K2-222b, we measure a mass of 8.0 ± 1.8 M and a radius of 2.35 ± 0.08 R . According to model predictions, K2-79b is a highly irradiated Uranus analog and K2-222b hosts significant amounts of water ice. We also present a RV solution for a candidate second companion orbiting K2-222 at 147.5 days.

Exoplanet astronomyStellar activityNASA Exoplanet Research ProgramNNX17AB59Gccc0004-6256/22/41+24$33.00crossmarkyes