Characterization of K2-167 b and CALM, a new stellar activity mitigation method

Zoe. L. De beurs; Andrew M. Vanderburg; Erica Thygesen; Joseph E. Rodriguez; Xavier Dumusque; Annelies Mortier; Luca Malavolta; Lars A. Buchhave; Christopher J. Shallue; Sebastian Zieba; L Kreidberg; John H. Livingston; R. D. Haywood; David W. Latham; Mercedes López-Morales; André M. Silva

doi:10.1093/mnras/stae207

Characterization of K2-167 b and CALM, a new stellar activity mitigation method

Zoe. L. De beurs^*, Andrew M. Vanderburg, Erica Thygesen, Joseph E. Rodriguez, Xavier Dumusque, Annelies Mortier, Luca Malavolta, Lars A. Buchhave, Christopher J. Shallue, Sebastian Zieba, L Kreidberg, John H. Livingston, R. D. Haywood, David W. Latham, Mercedes López-Morales, André M. Silva

^*Corresponding author for this work

Physics and Astronomy

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Abstract

We report precise radial velocity (RV) observations of HD 212657 (= K2-167), a star shown by K2 to host a transiting sub-Neptune-sized planet in a 10 day orbit. Using Transiting Exoplanet Survey Satellite (TESS) photometry, we refined the planet parameters, especially the orbital period. We collected 74 precise RVs with the HARPS-N spectrograph between August 2015 and October 2016. Although this planet was first found to transit in 2015 and validated in 2018, excess RV scatter originally limited mass measurements. Here, we measure a mass by taking advantage of reductions in scatter from updates to the HARPS-N Data Reduction System (2.3.5) and our new activity mitigation method called CCF Activity Linear Model (CALM), which uses activity-induced line shape changes in the spectra without requiring timing information. Using the CALM framework, we performed a joint fit with RVs and transits using EXOFASTv2 and find $M_p = 6.3_{-1.4}^{+1.4}$ $M_{\oplus}$ and $R_p = 2.33^{+0.17}_{-0.15}$ $R_{\oplus}$, which places K2-167 b at the upper edge of the radius valley. We also find hints of a secondary companion at a $\sim$ 22 day period, but confirmation requires additional RVs. Although characterizing lower-mass planets like K2-167 b is often impeded by stellar variability, these systems especially help probe the formation physics (i.e. photoevaporation, core-powered mass loss) of the radius valley. In the future, CALM or similar techniques could be widely applied to FGK-type stars, help characterize a population of exoplanets surrounding the radius valley, and further our understanding of their formation.

Original language	English
Article number	stae207
Journal	Monthly Notices of the Royal Astronomical Society
Early online date	19 Jan 2024
DOIs	https://doi.org/10.1093/mnras/stae207
Publication status	E-pub ahead of print - 19 Jan 2024

Bibliographical note

20 pages, 16 figures, accepted for publication in MNRAS

ACKNOWLEDGEMENTS We acknowledge helpful conversations and feedback from members of Dave Latham’s Coffee Club. We thank Dr. Sai Ravela for fruitful discussions on the best ways to choose the model input parameters and suggesting future directions for refining our process. The HARPS-N project has been funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origins of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), and the Italian National Astrophysical Institute (INAF), the University of St Andrews, Queen’s University Belfast, and the University of Edinburgh. ZLD would like to thank the generous support of the MIT Presidential Fellowship, the MIT Collamore-Rogers Fellowship and to acknowledge that this material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1745302. ZLD and AV acknowledge support from the TESS Guest Investigator Program under NASA grant 80NSSC19K0388. ZLD and AV acknowledge support from the D.17 Extreme Precision Radial Velocity Foundation Science program under NASA grant 80NSSC22K0848. AMS would like to acknowledge that this work was supported by FCT-Fundação para a Ciência e a Tecnologia through national funds by these grants: UIDB/04434/2020; UIDP/04434/2020". Funded/Cofunded by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. A.M.S acknowledges support from the Fundação para a Ciência e a Tecnologia (FCT) through the Fellowship 2020.05387.BD. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC)’s Ernest Rutherford Fellowship (grant number ST/V004735/1). This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

Keywords

astro-ph.EP
astro-ph.IM
astro-ph.SR

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Cite this

De beurs, Z. L., Vanderburg, A. M., Thygesen, E., Rodriguez, J. E., Dumusque, X., Mortier, A., Malavolta, L., Buchhave, L. A., Shallue, C. J., Zieba, S., Kreidberg, L., Livingston, J. H., Haywood, R. D., Latham, D. W., López-Morales, M., & Silva, A. M. (2024). Characterization of K2-167 b and CALM, a new stellar activity mitigation method. Monthly Notices of the Royal Astronomical Society, Article stae207. Advance online publication. https://doi.org/10.1093/mnras/stae207

@article{8996ff1e0aa54a82b8d50840079d312f,

title = "Characterization of K2-167 b and CALM, a new stellar activity mitigation method",

abstract = " We report precise radial velocity (RV) observations of HD 212657 (= K2-167), a star shown by K2 to host a transiting sub-Neptune-sized planet in a 10 day orbit. Using Transiting Exoplanet Survey Satellite (TESS) photometry, we refined the planet parameters, especially the orbital period. We collected 74 precise RVs with the HARPS-N spectrograph between August 2015 and October 2016. Although this planet was first found to transit in 2015 and validated in 2018, excess RV scatter originally limited mass measurements. Here, we measure a mass by taking advantage of reductions in scatter from updates to the HARPS-N Data Reduction System (2.3.5) and our new activity mitigation method called CCF Activity Linear Model (CALM), which uses activity-induced line shape changes in the spectra without requiring timing information. Using the CALM framework, we performed a joint fit with RVs and transits using EXOFASTv2 and find $M_p = 6.3_{-1.4}^{+1.4}$ $M_{\oplus}$ and $R_p = 2.33^{+0.17}_{-0.15}$ $R_{\oplus}$, which places K2-167 b at the upper edge of the radius valley. We also find hints of a secondary companion at a $\sim$ 22 day period, but confirmation requires additional RVs. Although characterizing lower-mass planets like K2-167 b is often impeded by stellar variability, these systems especially help probe the formation physics (i.e. photoevaporation, core-powered mass loss) of the radius valley. In the future, CALM or similar techniques could be widely applied to FGK-type stars, help characterize a population of exoplanets surrounding the radius valley, and further our understanding of their formation. ",

keywords = "astro-ph.EP, astro-ph.IM, astro-ph.SR",

author = "{De beurs}, {Zoe. L.} and Vanderburg, {Andrew M.} and Erica Thygesen and Rodriguez, {Joseph E.} and Xavier Dumusque and Annelies Mortier and Luca Malavolta and Buchhave, {Lars A.} and Shallue, {Christopher J.} and Sebastian Zieba and L Kreidberg and Livingston, {John H.} and Haywood, {R. D.} and Latham, {David W.} and Mercedes L{\'o}pez-Morales and Silva, {Andr{\'e} M.}",

note = "20 pages, 16 figures, accepted for publication in MNRAS ACKNOWLEDGEMENTS We acknowledge helpful conversations and feedback from members of Dave Latham{\textquoteright}s Coffee Club. We thank Dr. Sai Ravela for fruitful discussions on the best ways to choose the model input parameters and suggesting future directions for refining our process. The HARPS-N project has been funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origins of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), and the Italian National Astrophysical Institute (INAF), the University of St Andrews, Queen{\textquoteright}s University Belfast, and the University of Edinburgh. ZLD would like to thank the generous support of the MIT Presidential Fellowship, the MIT Collamore-Rogers Fellowship and to acknowledge that this material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1745302. ZLD and AV acknowledge support from the TESS Guest Investigator Program under NASA grant 80NSSC19K0388. ZLD and AV acknowledge support from the D.17 Extreme Precision Radial Velocity Foundation Science program under NASA grant 80NSSC22K0848. AMS would like to acknowledge that this work was supported by FCT-Funda{\c c}{\~a}o para a Ci{\^e}ncia e a Tecnologia through national funds by these grants: UIDB/04434/2020; UIDP/04434/2020{"}. Funded/Cofunded by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. A.M.S acknowledges support from the Funda{\c c}{\~a}o para a Ci{\^e}ncia e a Tecnologia (FCT) through the Fellowship 2020.05387.BD. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC){\textquoteright}s Ernest Rutherford Fellowship (grant number ST/V004735/1). This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.",

year = "2024",

month = jan,

day = "19",

doi = "10.1093/mnras/stae207",

language = "English",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

publisher = "SIPRI/Oxford University Press",

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De beurs, ZL, Vanderburg, AM, Thygesen, E, Rodriguez, JE, Dumusque, X, Mortier, A, Malavolta, L, Buchhave, LA, Shallue, CJ, Zieba, S, Kreidberg, L, Livingston, JH, Haywood, RD, Latham, DW, López-Morales, M & Silva, AM 2024, 'Characterization of K2-167 b and CALM, a new stellar activity mitigation method', Monthly Notices of the Royal Astronomical Society. https://doi.org/10.1093/mnras/stae207

TY - JOUR

T1 - Characterization of K2-167 b and CALM, a new stellar activity mitigation method

AU - De beurs, Zoe. L.

AU - Vanderburg, Andrew M.

AU - Thygesen, Erica

AU - Rodriguez, Joseph E.

AU - Dumusque, Xavier

AU - Mortier, Annelies

AU - Malavolta, Luca

AU - Buchhave, Lars A.

AU - Shallue, Christopher J.

AU - Zieba, Sebastian

AU - Kreidberg, L

AU - Livingston, John H.

AU - Haywood, R. D.

AU - Latham, David W.

AU - López-Morales, Mercedes

AU - Silva, André M.

N1 - 20 pages, 16 figures, accepted for publication in MNRAS ACKNOWLEDGEMENTS We acknowledge helpful conversations and feedback from members of Dave Latham’s Coffee Club. We thank Dr. Sai Ravela for fruitful discussions on the best ways to choose the model input parameters and suggesting future directions for refining our process. The HARPS-N project has been funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origins of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), and the Italian National Astrophysical Institute (INAF), the University of St Andrews, Queen’s University Belfast, and the University of Edinburgh. ZLD would like to thank the generous support of the MIT Presidential Fellowship, the MIT Collamore-Rogers Fellowship and to acknowledge that this material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1745302. ZLD and AV acknowledge support from the TESS Guest Investigator Program under NASA grant 80NSSC19K0388. ZLD and AV acknowledge support from the D.17 Extreme Precision Radial Velocity Foundation Science program under NASA grant 80NSSC22K0848. AMS would like to acknowledge that this work was supported by FCT-Fundação para a Ciência e a Tecnologia through national funds by these grants: UIDB/04434/2020; UIDP/04434/2020". Funded/Cofunded by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. A.M.S acknowledges support from the Fundação para a Ciência e a Tecnologia (FCT) through the Fellowship 2020.05387.BD. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC)’s Ernest Rutherford Fellowship (grant number ST/V004735/1). This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

PY - 2024/1/19

Y1 - 2024/1/19

N2 - We report precise radial velocity (RV) observations of HD 212657 (= K2-167), a star shown by K2 to host a transiting sub-Neptune-sized planet in a 10 day orbit. Using Transiting Exoplanet Survey Satellite (TESS) photometry, we refined the planet parameters, especially the orbital period. We collected 74 precise RVs with the HARPS-N spectrograph between August 2015 and October 2016. Although this planet was first found to transit in 2015 and validated in 2018, excess RV scatter originally limited mass measurements. Here, we measure a mass by taking advantage of reductions in scatter from updates to the HARPS-N Data Reduction System (2.3.5) and our new activity mitigation method called CCF Activity Linear Model (CALM), which uses activity-induced line shape changes in the spectra without requiring timing information. Using the CALM framework, we performed a joint fit with RVs and transits using EXOFASTv2 and find $M_p = 6.3_{-1.4}^{+1.4}$ $M_{\oplus}$ and $R_p = 2.33^{+0.17}_{-0.15}$ $R_{\oplus}$, which places K2-167 b at the upper edge of the radius valley. We also find hints of a secondary companion at a $\sim$ 22 day period, but confirmation requires additional RVs. Although characterizing lower-mass planets like K2-167 b is often impeded by stellar variability, these systems especially help probe the formation physics (i.e. photoevaporation, core-powered mass loss) of the radius valley. In the future, CALM or similar techniques could be widely applied to FGK-type stars, help characterize a population of exoplanets surrounding the radius valley, and further our understanding of their formation.

AB - We report precise radial velocity (RV) observations of HD 212657 (= K2-167), a star shown by K2 to host a transiting sub-Neptune-sized planet in a 10 day orbit. Using Transiting Exoplanet Survey Satellite (TESS) photometry, we refined the planet parameters, especially the orbital period. We collected 74 precise RVs with the HARPS-N spectrograph between August 2015 and October 2016. Although this planet was first found to transit in 2015 and validated in 2018, excess RV scatter originally limited mass measurements. Here, we measure a mass by taking advantage of reductions in scatter from updates to the HARPS-N Data Reduction System (2.3.5) and our new activity mitigation method called CCF Activity Linear Model (CALM), which uses activity-induced line shape changes in the spectra without requiring timing information. Using the CALM framework, we performed a joint fit with RVs and transits using EXOFASTv2 and find $M_p = 6.3_{-1.4}^{+1.4}$ $M_{\oplus}$ and $R_p = 2.33^{+0.17}_{-0.15}$ $R_{\oplus}$, which places K2-167 b at the upper edge of the radius valley. We also find hints of a secondary companion at a $\sim$ 22 day period, but confirmation requires additional RVs. Although characterizing lower-mass planets like K2-167 b is often impeded by stellar variability, these systems especially help probe the formation physics (i.e. photoevaporation, core-powered mass loss) of the radius valley. In the future, CALM or similar techniques could be widely applied to FGK-type stars, help characterize a population of exoplanets surrounding the radius valley, and further our understanding of their formation.

KW - astro-ph.EP

KW - astro-ph.IM

KW - astro-ph.SR

U2 - 10.1093/mnras/stae207

DO - 10.1093/mnras/stae207

M3 - Article

SN - 0035-8711

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

M1 - stae207

ER -

Characterization of K2-167 b and CALM, a new stellar activity mitigation method

Abstract

Bibliographical note

Keywords

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