Volume 584, December 2015
|Number of page(s)||12|
|Section||Planets and planetary systems|
|Published online||24 November 2015|
The HARPS-N Rocky Planet Search
I. HD 219134 b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun ⋆
Observatoire de Genève, Université de Genève, 51 chemin des
2 Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
4 Centre for Stars and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen, Denmark
5 Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
6 Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universita di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
7 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
8 SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH93 HJ, UK
9 SUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews Fife, KY16 9SS, UK
10 INAF–Fundación Galileo Galilei, Rambla José Ana Fernandez Pérez 7, 38712 Berña Baja, Spain
11 INAF–IASF Milano, via Bassini 15, 20133 Milano, Italy
12 INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
13 INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
14 Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
15 Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
16 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN, UK
Received: 24 June 2015
Accepted: 30 July 2015
We know now from radial velocity surveys and transit space missions that planets only a few times more massive than our Earth are frequent around solar-type stars. Fundamental questions about their formation history, physical properties, internal structure, and atmosphere composition are, however, still to be solved. We present here the detection of a system of four low-mass planets around the bright (V = 5.5) and close-by (6.5 pc) star HD 219134. This is the first result of the Rocky Planet Search programme with HARPS-N on the Telescopio Nazionale Galileo in La Palma. The inner planet orbits the star in 3.0935 ± 0.0003 days, on a quasi-circular orbit with a semi-major axis of 0.0382 ± 0.0003 AU. Spitzer observations allowed us to detect the transit of the planet in front of the star making HD 219134 b the nearest known transiting planet to date. From the amplitude of the radial velocity variation (2.25 ± 0.22 ms-1) and observed depth of the transit (359 ± 38 ppm), the planet mass and radius are estimated to be 4.36 ± 0.44 M⊕ and 1.606 ± 0.086 R⊕, leading to a mean density of 5.76 ± 1.09 g cm-3, suggesting a rocky composition. One additional planet with minimum-mass of 2.78 ± 0.65 M⊕ moves on a close-in, quasi-circular orbit with a period of 6.767 ± 0.004 days. The third planet in the system has a period of 46.66 ± 0.08 days and a minimum-mass of 8.94 ± 1.13 M⊕, at 0.233 ± 0.002 AU from the star. Its eccentricity is 0.46 ± 0.11. The period of this planet is close to the rotational period of the star estimated from variations of activity indicators (42.3 ± 0.1 days). The planetary origin of the signal is, however, thepreferred solution as no indication of variation at the corresponding frequency is observed for activity-sensitive parameters. Finally, a fourth additional longer-period planet of mass of 71 M⊕ orbits the star in 1842 days, on an eccentric orbit (e = 0.34 ± 0.17) at a distance of 2.56 AU.
Key words: techniques: radial velocities / techniques: photometric / stars: individual: HD 219134 / binaries: eclipsing / instrumentation: spectrographs
The photometric time series and radial velocities used in this work are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A72
© ESO, 2015
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