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Published December 2016 | Published + Submitted
Journal Article Open

Kepler-21b: A Rocky Planet Around a V = 8.25 Magnitude Star

Abstract

HD 179070, aka Kepler-21, is a V = 8.25 F6IV star and the brightest exoplanet host discovered by Kepler. An early detailed analysis by Howell et al. of the first 13 months (Q0–Q5) of Kepler light curves revealed transits of a planetary companion, Kepler-21b, with a radius of about 1.60 ± 0.04 R⊕ and an orbital period of about 2.7857 days. However, they could not determine the mass of the planet from the initial radial velocity (RV) observations with Keck-HIRES, and were only able to impose a 2σ upper limit of 10 M⊕. Here, we present results from the analysis of 82 new RV observations of this system obtained with HARPS-N, together with the existing 14 HIRES data points. We detect the Doppler signal of Kepler-21b with a RV semiamplitude K = 2.00 ± 0.65 m s^(-1), which corresponds to a planetary mass of 5.1 ± 1.7 M⊕. We also measure an improved radius for the planet of 1.639 +0.019/−0.015 R⊕, in agreement with the radius reported by Howell et al. We conclude that Kepler-21b, with a density of 6.4 ± 2.1 g cm^(-3), belongs to the population of small, ≾6 M⊕ planets with iron and magnesium silicate interiors, which have lost the majority of their envelope volatiles via stellar winds or gravitational escape. The RV analysis presented in this paper serves as an example of the type of analysis that will be necessary to confirm the masses of TESS small planet candidates.

Additional Information

© 2016 The American Astronomical Society. Received 2016 August 15; revised 2016 September 14; accepted 2016 September 22; published 2016 December 2. Based on observations made with the Italian Telescope Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. We thank the anonymous referee for helpful comments to the manuscript. 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, Queens University Belfast, and the University of Edinburgh. This publication was made possible through the support of 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. This material is based upon work supported by the National Aeronautics and Space Administration under grant No. NNX15AC90G 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). 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. P.F. acknowledges support by Fundação para a Cîencias e a Tecnologia (FCT) through Investigador FCT contract of reference IF/01037/2013 and POPH/FSE (EC) by FEDER funding through the program "Programa Operacional de Factores de Competitividade - COMPETE", and further support in the form of an exploratory project of reference IF/01037/2013CP1191/CT0001. L.Z. is supported by a grant from the Simons Foundation (SCOL, award #337090). A.V. is supported by the NSF Graduate Research Fellowship, Grant No. DGE 1144152. X.D. is grateful to the Society in Science-Branco Weiss Fellowship for its financial support. Facilities: TNG: HARPS-N, Keck: HIRES, TRES.

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Published - López-Morales_2016_AJ_152_204.pdf

Submitted - 1609.07617v1.pdf

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Additional details

Created:
August 19, 2023
Modified:
October 23, 2023