K2-291b: A Rocky Super-Earth in a 2.2 day Orbit

Creators: Kosiarek, Molly R.; Blunt, Sarah; Lopez-Morales, Mercedes; Crossfield, Ian J. M.; Sinukoff, Evan; Petigura, Erik A.; Gonzales, Erica J.; Poretti, Ennio; Malavolta, Luca; Howard, Andrew W.; Isaacson, Howard; Haywood, Raphaelle D.; Ciardi, David R.; Bristow, Makennah; Cameron, Andrew Collier; Charbonneau, David; Dressing, Courtney D.; Figueira, Pedro; Fulton, Benjamin J.; Hardee, Bronwen J.; Hirsch, Lea A.; Latham, David W.; Mortier, Annelies; Nava, Chantanelle; Schlieder, Joshua E.; Vanderburg, Andrew; Weiss, Lauren; Bonomo, Aldo S.; Bouchy, Francois; Buchhave, Lars A.; Coffinet, Adrien; Damasso, Mario; Dumusque, Xavier; Lovis, Christophe; Mayor, Michel; Micela, Giusi; Molinari, Emilio; Pepe, Francesco; Phillips, David; Piotto, Giampaolo; Rice, Ken; Sasselov, Dimitar; Segransan, Damien; Sozzetti, Alessandro; Udry, Stephane; Watson, Chris

Abstract

K2-291 is a solar-type star with a radius of R * = 0.899 ± 0.034 R ⊙ and mass of M* = 0.934 ± 0.038 M⊙. From the K2 C13 data, we found one super-Earth planet (R_p = 1.589^(+0.095)_(-0.072) R⊕) transiting this star on a short period orbit (P = 2.225177^(6.6e-5)_(-6.8e5) days). We followed this system up with adaptive-optic imaging and spectroscopy to derive stellar parameters, search for stellar companions, and determine a planet mass. From our 75 radial velocity measurements using High Resolution Echelle Spectrometer on Keck I and High Accuracy Radial velocity Planet Searcher in the northern hemisphere on Telescopio Nazionale Galileo, we constrained the mass of K2-291 b to M_p = 6.49 ± 1.16 M⊕. We found it necessary to model correlated stellar activity radial velocity signals with a Gaussian process (GP) in order to more accurately model the effect of stellar noise on our data; the addition of the GP also improved the precision of this mass measurement. With a bulk density of ρ = 8.84^(+2.50)_(-2.03) g cm^(−3), the planet is consistent with an Earth-like rock/iron composition and no substantial gaseous envelope. Such an envelope, if it existed in the past, was likely eroded away by photoevaporation during the first billion years of the star's lifetime.

Additional Information

© 2019 The American Astronomical Society. Received 2018 August 16; revised 2019 January 3; accepted 2019 January 9; published 2019 February 13. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. Keck time has been granted by NASA, the University of Hawaii, the California Institute of Technology, and the University of California. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain). 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. A.W.H., I.J.M.C., and C.D.D. acknowledge support from the K2 Guest Observer Program. A.W.H. acknowledges support for our K2 team through a NASA Astrophysics Data Analysis Program grant and observing support from NASA at Keck Observatory. This work was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute (R.D.H., C.D.D., A.V.). Some of this work has been carried out within the framework of the NCCR PlanetS, supported by the Swiss National Science Foundation. M.R.K is supported by the NSF Graduate Research Fellowhsip, grant No. DGE 1339067. A.C.C. acknowledges support from STFC consolidated grant number ST/M001296/1. D.W.L. acknowledges partial support from the Kepler mission under NASA Cooperative Agreement NNX13AB58A with the Smithsonian Astrophysical Observatory. X.D. is grateful to the Society in Science-Branco Weiss Fellowship for its financial support. C.A.W. acknowledges support by STFC grant ST/P000312/1. L.M. acknowledges the support by INAF/Frontiera through the Progetti Premiali funding scheme of the Italian Ministry of Education, University, and Research. This material is based upon work supported by the National Aeronautics and Space Administration under grants No. NNX15AC90G and NNX17AB59G issued through the Exoplanets Research Program. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant Agreement No. 313014 (ETAEARTH). 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. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. This research has made use of NASA's Astrophysics Data System and 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. This research has made use of the corner.py code by Dan Foreman-Mackey at github.com/dfm/corner.py. This publication received support from a grant from the John Templeton Foundation. The opinions expressed are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Kepler/K2 Keck TNG:HARPS-N. Software: batman (Kreidberg 2015), corner.py (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), isoclassify (Huber et al. 2017), k2phot, scipy (Jones et al. 2001), PyORBIT (Malavolta et al. 2016, 2018), RadVel (Fulton et al. 2018), ReaMatch algorithm (Kolbl et al. 2015), SpecMatch-Syn (Petigura 2015), Spectroscopy Made Easy (SME) (Valenti & Piskunov 2012; Piskunov & Valenti 2017), TERRA algorithm (Petigura et al. 2018).

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