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. (2012) of the first thirteen 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_earth and an orbital period of about 2.7857 days. However, they could not determine the mass of the planet from the initial radial velocity observations with Keck-HIRES, and were only able to impose a 2-sigma upper limit of 10 M_earth. Here we present results from the analysis of 82 new radial velocity 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 radial velocity semi-amplitude K = 2.00 +/- 0.65 m/s, which corresponds to a planetary mass of 5.1 +/- 1.7 M_earth. We also measure an improved radius for the planet of 1.639 (+0.019, -0.015) R_earth, in agreement with the radius reported by Howell et al. (2012). We conclude that Kepler-21b, with a density of 6.4 +/- 2.1 g/cm^3, belongs to the population of terrestrial planets with iron, magnesium silicate interiors, which have lost the majority of their envelope volatiles via stellar winds or gravitational escape. The radial velocity analysis presented in this paper serves as example of the type of analysis that will be necessary to confirm the masses of TESS small planet candidates.

52 pages, 13 figures, 1 long table. Accepted for publication in ApJ

References in corpus (20)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Most 1.6 Earth-Radius Planets are not Rocky
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Three regimes of extrasolar planets inferred from host star metallicities
• The Broadband Infrared Emission Spectrum of the Exoplanet HD 189733b
• Exoplanet population inference and the abundance of Earth analogs from noisy, incomplete catalogs
• The Mass of Kepler-93b and The Composition of Terrestrial Planets
• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
• A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars
• Correcting the spectroscopic surface gravity using transits and asteroseismology. No significant effect on temperatures or metallicities with ARES+MOOG in LTE
• A 1.9 Earth radius rocky planet and the discovery of a non-transiting planet in the Kepler-20 system
• Revisiting the transits of CoRoT-7b at a lower activity level
• The GAPS Programme with HARPS-N at TNG. III: The retrograde orbit of HAT-P-18b
• The GAPS programme with HARPS-N@TNG IV: A planetary system around XO-2S
• Rossiter-McLaughlin Observations of 55 Cnc e
• Characterization of the Kepler-101 planetary system with HARPS-N. A hot super-Neptune with an Earth-sized low-mass companion
• The GAPS Programme with HARPS-N@TNG VI: The Curious Case of TrES-4b

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