Kepler-21b: A 1.6R_Earth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070

S. B. Howell, J. F. Rowe, S. T. Bryson, S. N. Quinn, G. W. Marcy, H. Isaacson, D. Ciardi, W. J. Chaplin, T. S. Metcalfe, M. J. P. F. G. Monteiro, T. Appourchaux, S. Basu, O. L. Creevey, R. L. Gilliland, P.-O. Quirion, D. Stello, H. Kjeldsen, J. Christensen-Dalsgaard, Y. Elsworth, R. A. García, G. Houdek, C. Karoff, J. Molenda-Żakowicz, M. J. Thompson, G. A. Verner, G. Torres, F. Fressin, J. R. Crepp, E. Adams, A. Dupree, D. Sasselov, C. D. Dressing, W. J. Borucki, D. Koch, J. J. Lissauer, D. W. Latham, T. N. Gautier III, M. Everett, E. P. Horch, N. Batalha, E. W. Dunham, P. Szkody, D. R. Silva, K. Mighell, J. Holberg, J. Ballot, T. R. Bedding, H. Bruntt, T. L. Campante, R. Handberg, S. Hekker, D. Huber, S. Mathur, B. Mosser, C. Régulo, T. R. White, J. L. Christiansen, C. K. Middour, M. R. Haas, J. R. Hall, J. M. Jenkins, S. McCauliff, M. N. Fanelli, C. Kulesa, D. McCarthy, C. E. Henze

Abstract
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 frequencypower 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&plusmin;0.06 M_☉ and 1.86&plusmin;0.04 R_☉ respectively, as well as yielding an age of 2.84&plusmin;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&plusmin;0.04 R_Earth exoplanet in a 2.785755&plusmin;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 MEarth (2-σ). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.

Keywords
planetary systems – stars: activity – stars: individual (HD 179070: KIC 3632418) – stars: interiors – stars: late-type – stars: magnetic field – stars: oscillations (including pulsations) 

The Astrophysical Journal
Volume 746, Page 123_1
February 2012

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