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arXiv · 1703.01430

Two massive rocky planets transiting a K-dwarf 6.5 parsecs away

Michael Gillon·Brice-Olivier Demory·Valerie Van Grootel·Fatemeh Motalebi·Christophe Lovis·Andrew Collier Cameron·David Charbonneau·David Latham·Emilio Molinari·Francesco A. Pepe·Damien Segransan·Dimitar Sasselov·Stephane Udry·Michel Mayor·Giuseppina Micela·Giampaolo Piotto·Alessandro Sozzetti
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Abstract

HD 219134 is a K-dwarf star at a distance of 6.5 parsecs around which several low-mass planets were recently discovered. The Spitzer space telescope detected a transit of the innermost of these planets, HD 219134 b, whose mass and radius (4.5 MEarth and 1.6 REarth respectively) are consistent with a rocky composition. Here, we report new highprecision time-series photometry of the star acquired with Spitzer revealing that the second innermost planet of the system, HD 219134 c, is also transiting. A global analysis of the Spitzer transit light curves and the most up-to-date HARPS-N velocity data set yields mass and radius estimations of 4.74+-0.19 MEarth and 1.602+-0.055 REarth for HD 219134 b, and of 4.36+-0.22 MEarth and 1.511+-0.047 REarth for HD 219134 c. These values suggest rocky compositions for both planets. Thanks to the proximity and the small size of their host star (0.778+-0.005 Rsun), these two transiting exoplanets - the nearest to the Earth to date - are well-suited for a detailed characterization (precision of a few percent on mass and radius, constraints on the atmospheric properties...) that could give important constraints on the nature and formation mechanism of the ubiquitous short-period planets of a few Earth masses.

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Michael Gillon, Brice-Olivier Demory, Valerie Van Grootel, Fatemeh Motalebi, Christophe Lovis, Andrew Collier Cameron, David Charbonneau, David Latham, Emilio Molinari, Francesco A. Pepe, Damien Segransan, Dimitar Sasselov, Stephane Udry, Michel Mayor, Giuseppina Micela, Giampaolo Piotto, Alessandro Sozzetti. 2017-03-04. Two massive rocky planets transiting a K-dwarf 6.5 parsecs away. https://doi.org/10.1038/s41550-017-0056

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