K2-79b and K2-222b: Mass Measurements of Two Small Exoplanets with Periods beyond 10 days that Overlap with Periodic Magnetic Activity Signals

Chantanelle Nava*, Mercedes López-Morales, Annelies Mortier, Li Zeng, Helen A. C. Giles, Allyson Bieryla, Andrew Vanderburg, Lars A. Buchhave, Ennio Poretti, Steven H. Saar, Xavier Dumusque, David W. Latham, David Charbonneau, Mario Damasso, Aldo S. Bonomo, Christophe Lovis, Andrew Collier Cameron, Jason D. Eastman, Alessandro Sozzetti, Rosario CosentinoMarco Pedani, Francesco Pepe, Emilio Molinari, Dimitar Sasselov, Michel Mayor, Manu Stalport, Luca Malavolta, Ken Rice, Christopher A. Watson, A. F. Martinez Fiorenzano, Luca Di Fabrizio

*Corresponding author for this work

    Research output: Contribution to journalJournal articleResearchpeer-review

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    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.
    Original languageEnglish
    Article number41
    JournalAstronomical Journal
    Volume163
    Issue number2
    Number of pages23
    ISSN0004-6256
    DOIs
    Publication statusPublished - 2022

    Keywords

    • Exoplanet astronomy
    • Stellar activity

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