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 Cosentino; Marco 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

doi:10.3847/1538-3881/ac3141

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 journal › Article › peer-review

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 language	English
Article number	41
Number of pages	23
Journal	Astronomical Journal
Volume	163
Issue number	2
Early online date	4 Jan 2022
DOIs	https://doi.org/10.3847/1538-3881/ac3141
Publication status	Published - 1 Feb 2022

Keywords

Exoplanet astronomy
Stellar activity

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Nava_2022_AJ_K2-89b-and-K2-222b_CC
Copyright © 2022. The Author(s). Published by the American Astronomical Society. 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.
Final published version, 3.15 MBLicence: CC BY

https://arxiv.org/abs/2111.02608

Support for the PLATO Development: Support for the PLATO Development Phase 2017-2022: Planet candidate ranking and validation
Cameron, A. C. (PI)
Science & Technology Facilities Council
1/08/17 → 31/12/22
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Nava, C., López-Morales, M., Mortier, A., Zeng, L., Giles, H. A. C., Bieryla, A., Vanderburg, A., Buchhave, L. A., Poretti, E., Saar, S. H., Dumusque, X., Latham, D. W., Charbonneau, D., Damasso, M., Bonomo, A. S., Lovis, C., Collier Cameron, A., Eastman, J. D., Sozzetti, A., ... Di Fabrizio, L. (2022). K2-79b and K2-222b: mass measurements of two small exoplanets with periods beyond 10 days that overlap with periodic magnetic activity signals. Astronomical Journal, 163(2), Article 41. https://doi.org/10.3847/1538-3881/ac3141

@article{765e15e5077349bc96b59e37293f586c,

title = "K2-79b and K2-222b: mass measurements of two small exoplanets with periods beyond 10 days that overlap with periodic magnetic activity signals",

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.",

keywords = "Exoplanet astronomy, Stellar activity",

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

note = "Funding: The HARPS-N project was funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origin of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), University of St. Andrews, Queen's University Belfast, and University of Edinburgh. This work has been supported by the National Aeronautics and Space Administration under grant No. NNX17AB59G, issued through the Exoplanets Research Program. Parts of this work have been supported by the Brinson Foundation. A.Mo. acknowledges support from the senior Kavli Institute Fellowships. C.A.W. acknowledges support from Science and Technology Facilities Council (STFC) grant No. ST/P000312/1. S.H.S. acknowledges support by NASA Heliophysics LWS grant No. NNX16AB79G. L.Z. acknowledges support by the Sandia Z. Fundamental Science Program by the Department of Energy National Nuclear Security Administration under Awards DE-NA0003904 (to S.B.J.) (principal investigator) with Harvard University.",

year = "2022",

month = feb,

day = "1",

doi = "10.3847/1538-3881/ac3141",

language = "English",

volume = "163",

journal = "Astronomical Journal",

issn = "0004-6256",

publisher = "American Astronomical Society",

number = "2",

}

Nava, C, López-Morales, M, Mortier, A, Zeng, L, Giles, HAC, Bieryla, A, Vanderburg, A, Buchhave, LA, Poretti, E, Saar, SH, Dumusque, X, Latham, DW, Charbonneau, D, Damasso, M, Bonomo, AS, Lovis, C, Collier Cameron, A, Eastman, JD, Sozzetti, A, Cosentino, R, Pedani, M, Pepe, F, Molinari, E, Sasselov, D, Mayor, M, Stalport, M, Malavolta, L, Rice, K, Watson, CA, Martinez Fiorenzano, AF & Di Fabrizio, L 2022, 'K2-79b and K2-222b: mass measurements of two small exoplanets with periods beyond 10 days that overlap with periodic magnetic activity signals', Astronomical Journal, vol. 163, no. 2, 41. https://doi.org/10.3847/1538-3881/ac3141

TY - JOUR

T1 - K2-79b and K2-222b

T2 - mass measurements of two small exoplanets with periods beyond 10 days that overlap with periodic magnetic activity signals

AU - Nava, Chantanelle

AU - López-Morales, Mercedes

AU - Mortier, Annelies

AU - Zeng, Li

AU - Giles, Helen A. C.

AU - Bieryla, Allyson

AU - Vanderburg, Andrew

AU - Buchhave, Lars A.

AU - Poretti, Ennio

AU - Saar, Steven H.

AU - Dumusque, Xavier

AU - Latham, David W.

AU - Charbonneau, David

AU - Damasso, Mario

AU - Bonomo, Aldo S.

AU - Lovis, Christophe

AU - Collier Cameron, Andrew

AU - Eastman, Jason D.

AU - Sozzetti, Alessandro

AU - Cosentino, Rosario

AU - Pedani, Marco

AU - Pepe, Francesco

AU - Molinari, Emilio

AU - Sasselov, Dimitar

AU - Mayor, Michel

AU - Stalport, Manu

AU - Malavolta, Luca

AU - Rice, Ken

AU - Watson, Christopher A.

AU - Martinez Fiorenzano, A. F.

AU - Di Fabrizio, Luca

N1 - Funding: The HARPS-N project was funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origin of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), University of St. Andrews, Queen's University Belfast, and University of Edinburgh. This work has been supported by the National Aeronautics and Space Administration under grant No. NNX17AB59G, issued through the Exoplanets Research Program. Parts of this work have been supported by the Brinson Foundation. A.Mo. acknowledges support from the senior Kavli Institute Fellowships. C.A.W. acknowledges support from Science and Technology Facilities Council (STFC) grant No. ST/P000312/1. S.H.S. acknowledges support by NASA Heliophysics LWS grant No. NNX16AB79G. L.Z. acknowledges support by the Sandia Z. Fundamental Science Program by the Department of Energy National Nuclear Security Administration under Awards DE-NA0003904 (to S.B.J.) (principal investigator) with Harvard University.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - 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.

AB - 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.

KW - Exoplanet astronomy

KW - Stellar activity

U2 - 10.3847/1538-3881/ac3141

DO - 10.3847/1538-3881/ac3141

M3 - Article

SN - 0004-6256

VL - 163

JO - Astronomical Journal

JF - Astronomical Journal

IS - 2

M1 - 41

ER -

K2-79b and K2-222b: mass measurements of two small exoplanets with periods beyond 10 days that overlap with periodic magnetic activity signals

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Support for the PLATO Development: Support for the PLATO Development Phase 2017-2022: Planet candidate ranking and validation

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