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

Mercedes López-Morales, Raphaëlle D. Haywood, Jeffrey L. Coughlin, Li Zeng, Lars A. Buchhave, Helen A. C. Giles, Laura Affer, Aldo S. Bonomo, David Charbonneau, Andrew Collier Cameron, Rosario Consentino, Courtney D. Dressing, Xavier Dumusque, Pedro Figueira, Aldo F. M. Fiorenzano, Avet Harutyunyan, John Asher Johnson, David W. Latham, Eric D. Lopez, Christophe LovisLuca Malavolta, Michel Mayor, Giusi Micela, Emilio Molinari, Annelies Mortier, Fatemeh Motalebi, Valerio Nascimbeni, Francesco Pepe, David F. Phillips, Giampaolo Piotto, Don Pollacco, Didier Queloz, Ken Rice, Dimitar Sasselov, Damien Segransan, Alessandro Sozzetti, Stephane Udry, Andrew Vanderburg, Chris Watson

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

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}\oplus 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}\oplus . 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}\oplus . We also measure an improved radius for the planet of 1.639 +0.019/-0.015 {R}\oplus , 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}\oplus 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. 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.
Original languageEnglish
Pages (from-to)204
JournalAstronomical Journal
Issue number6
Publication statusPublished - 1 Dec 2016

Keywords / Materials (for Non-textual outputs)

  • planets and satellites: formation
  • planets and satellites: individual: Kepler-21b
  • stars: individual: HD 179070
  • techniques: photometric
  • techniques: radial velocities
  • techniques: spectroscopic


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