$Kepler$-21b: A 1.6 $R_{earth}$ planet transiting the bright oscillating F subgiant star HD 179070

Steve Howell (1, 2) , Jason Rowe (2) , Stephen Bryson (2) , Samuel Quinn (3) , Geoffrey Marcy (4) , Howard Isaacson (5) , David Ciardi (6) , William Chaplin (7, 8) , Travis Metcalfe (9) , Mario Monteiro (10) , Thierry Appourchaux (11) , Sarbani Basu (12) , Orlagh Creevey (13) , Ronald Gilliland , Pierre-Olivier Quirion (14) , Denis Stello , Hans Kjeldsen (15) , Jørgen Christensen-Dalsgaard (15) , Yvonne D Elsworth (16) , Rafael Garcia (17) , Günter Houdek (15) , Christoffer Karoff (18) , Joanna Molenda-Żakowicz (19) , Michael Thompson , Graham Verner , Guillermo Torres , François Fressin (20) , Justin Crepp , Elisabeth Adams , Andrea Dupree , Dimitar Sasselov , Courtney Dressing , William Borucki , David Koch (2) , Jack Lissauer (2) , David Latham , Lars Buchhave (21) , Thomas Gautier (22) , Mark Everett , Elliott Horch , Natalie Batalha , Edward Dunham , Paula Szkody , David Silva (23) , Ken Mighell , Jay Holberg , Jérôme Ballot (24) , Timothy R Bedding (25) , Hans Bruntt (25) , Tiago Campante , Rasmus Handberg (15) , Saskia Hekker (18) , Daniel Huber (26) , Savita Mathur (27) , Benoit Mosser (28) , Clara Régulo (29) , Timothy White , Jessie Christiansen , Christopher Middour , Michael Haas , Jennifer Hall , Jon Jenkins (2) , Sean Mccaulif , Michael Fanelli , Craig Kulesa , Don Mccarthy , Christopher Henze

1 NOAO - National Optical Astronomy Observatory
2 ARC - NASA Ames Research Center
3 CfA - Harvard-Smithsonian Center for Astrophysics
4 UC Berkeley - University of California [Berkeley]
5 EPS - Department of Earth and Planetary Science [UC Berkeley]
6 IPAC - Infrared Processing and Analysis Center
7 Department of Psychology
8 School of Physics and Astronomy [Birmingham]
9 Department of Space Studies [Boulder]
10 Universidade do Porto = University of Porto
11 IAS - Institut d'astrophysique spatiale
12 NUS - National University of Singapore
13 ULL - Universidad de La Laguna [Tenerife - SP]
14 CRIUGM - Centre de recherche de l'Institut universitaire de gériatrie de Montreal
15 SAC - Stellar Astrophysics Centre [Aarhus]
16 School of Physics and Astronomy [Birmingham]
17 VICOROB - Research institute of Computer Vision and Robotics [Girona]
18 School of Physics and Astronomy
19 Astronomical Institute [Wroclaw]
20 LG - Laboratoire Gemini
21 NBI - Niels Bohr Institute [Copenhagen]
22 JPL - Jet Propulsion Laboratory
23 CGUP - Geology Center of the University of Porto
24 IRAP - Institut de recherche en astrophysique et planétologie
25 SIfA - Sydney Institute for Astronomy
26 CLLE-ERSS - Cognition, Langues, Langage, Ergonomie
27 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
28 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
29 IAC - Instituto de Astrofisica de Canarias

We present $Kepler$ observations of the bright (V = 8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 $R_{earth}$ object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequency–power spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34 ± 0.06 M$_\odot$ and 1.86 ± 0.04 R$_\odot$, respectively, as well as yielding an age of 2.84 ± 0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3σ) that the transit event is caused by a 1.64 ± 0.04 $R_{earth}$ exoplanet in a 2.785755 ± 0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ∼10$M_{earth}$ (2σ). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.

Mots clés: Planetary systems; stars: activity; stars: individual (HD 179070: KIC 3632418); stars: interiors; stars: late-type; stars: magnetic field; stars: oscillations (including pulsations); techniques: photometric

Domaines: Physique [physics]; Astrophysique [astro-ph]

Steve Howell, Jason Rowe, Stephen Bryson, Samuel Quinn, Geoffrey Marcy, et al.. $Kepler$-21b: A 1.6 $R_{earth}$ planet transiting the bright oscillating F subgiant star HD 179070. The Astrophysical Journal, 2012, 746 (2), pp.123. ⟨10.1088/0004-637X/746/2/123⟩. ⟨hal-02909130⟩