[en] HD 219134 is a K-dwarf star at a distance of 6.5 parsecs around which several low-mass planets were recently discovered[SUP]1,2[/SUP]. The Spitzer Space Telescope detected a transit of the innermost of these planets, HD 219134 b, whose mass and radius (4.5 M[SUB]⊕[/SUB] and 1.6 R[SUB]⊕[/SUB] respectively) are consistent with a rocky composition[SUP]1[/SUP]. Here, we report new high-precision time-series photometry of the star acquired with Spitzer revealing that the second innermost planet of the system, HD 219134c, 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 M[SUB]⊕[/SUB] and 1.602 ± 0.055 R[SUB]⊕[/SUB] for HD 219134 b, and of 4.36 ± 0.22 M[SUB]⊕[/SUB] and 1.511 ± 0.047 R[SUB]⊕[/SUB] 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 R[SUB]⊙[/SUB])[SUP]3[/SUP], these two transiting exoplanets — the nearest to the Earth yet found — are well suited for a detailed characterization (for example, precision of a few per cent on mass and radius, and 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.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Gillon, Michaël ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Demory, Brice-Olivier
Van Grootel, Valérie ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie
Motalebi, Fatemeh; Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland
Lovis, Christophe; Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland
Cameron, Andrew Collier; Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews Fife, KY16 9SS, UK
Charbonneau, David; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
Latham, David; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
Molinari, Emilio; INAF — Fundación Galileo Galilei, Rambla José Ana Fernandez Pérez 7, 38712 Berña Baja, Spain ; INAF — IASF Milano, via Bassini 15, 20133 Milano, Italy
Pepe, Francesco A.; Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland
Ségransan, Damien; Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland
Sasselov, Dimitar; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
Udry, Stéphane; Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland
Mayor, Michel; Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland
Micela, Giuseppina; INAF — Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
Piotto, Giampaolo; Dipartimento di Fisica e Astronomia G. Galilei. Universitá di Padova, Vicolo dell'Osservatorio , 35122, Padova, Italy ; INAF — Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122, Padova, Italy
Sozzetti, Alessandro; INAF — Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy)
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