KEPLER-21B: a 1.6 Rearth PLANET TRANSITING the BRIGHT OSCILLATING F SUBGIANT STAR HD 179070 Steve B

The Astrophysical Journal, 746:123 (18pp), 2012 February 20 doi:10.1088/0004-637X/746/2/123 C 2012. The American Astronomical Society. All rights reserved. Printed in the U.S.A. ∗ KEPLER-21b: A 1.6 REarth PLANET TRANSITING THE BRIGHT OSCILLATING F SUBGIANT STAR HD 179070 Steve B. Howell1,2,36, Jason F. Rowe2,3,36, Stephen T. Bryson2, Samuel N. Quinn4, Geoffrey W. Marcy5, Howard Isaacson5, David R. Ciardi6, William J. Chaplin7, Travis S. Metcalfe8, Mario J. P. F. G. Monteiro9, Thierry Appourchaux10, Sarbani Basu11, Orlagh L. Creevey12,13, Ronald L. Gilliland14, Pierre-Olivier Quirion15, Denis Stello16, Hans Kjeldsen17,Jorgen¨ Christensen-Dalsgaard17, Yvonne Elsworth7, Rafael A. Garc´ıa18, Gunter¨ Houdek19, Christoffer Karoff7, Joanna Molenda-Zakowicz˙ 20, Michael J. Thompson8, Graham A. Verner7,21, Guillermo Torres4, Francois Fressin4, Justin R. Crepp23, Elisabeth Adams4, Andrea Dupree4, Dimitar D. Sasselov4, Courtney D. Dressing4, William J. Borucki2, David G. Koch2, Jack J. Lissauer2, David W. Latham4, Lars A. Buchhave22,35, Thomas N. Gautier III24, Mark Everett1, Elliott Horch25, Natalie M. Batalha26, Edward W. Dunham27, Paula Szkody28,36, David R. Silva1,36, Ken Mighell1,36, Jay Holberg29,36,Jeromeˆ Ballot30, Timothy R. Bedding16, Hans Bruntt12, Tiago L. Campante9,17, Rasmus Handberg17, Saskia Hekker7, Daniel Huber16, Savita Mathur8, Benoit Mosser31, Clara Regulo´ 12,13, Timothy R. White16, Jessie L. Christiansen3, Christopher K. Middour32, Michael R. Haas2, Jennifer R. Hall32,JonM.Jenkins3, Sean McCaulif32, Michael N. Fanelli33, Craig Kulesa34, Don McCarthy34, and Christopher E. Henze2 1 National Optical Astronomy Observatory, Tucson, AZ 85719, USA 2 NASA Ames Research Center, Moffett Field, CA 94035, USA 3 SETI Institute, Mountain View, CA 94043, USA 4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA 5 Department of Astronomy, University of California, Berkeley, CA 94720, USA 6 NASA Exoplanet Science Institute/Caltech, Pasadena, CA 91125, USA 7 School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK 8 High Altitude Observatory and Scientific Computing Division, National Center for Atmospheric Research, Boulder, CO 80307, USA 9 Centro de Astrof´ısica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal 10 Institut d’Astrophysique Spatiale, Universite´ Paris XI–CNRS (UMR8617), Batiment 121, 91405 Orsay Cedex, France 11 Department of Astronomy, Yale University, New Haven, CT 06520-8101, USA 12 Departamento de Astrof´ısica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain 13 Instituto de Astrof´ısica de Canarias, E-38200 La Laguna, Tenerife, Spain 14 Space Telescope Science Institute, Baltimore, MD 21218, USA 15 Canadian Space Agency, 6767 Boulevard de l’Aeroport,´ Saint-Hubert, QC, J3Y 8Y9, Canada 16 Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia 17 Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark 18 Laboratoire AIM, CEA/DSM–CNRS–Universite´ Paris Diderot-IRFU/SAp, 91191 Gif-sur-Yvette Cedex, France 19 Institute of Astronomy, University of Vienna, A-1180 Vienna, Austria 20 Astronomical Institute, University of Wrocław, 51-622 Wrocław, Poland 21 Astronomy Unit, Queen Mary, University of London, London E1 4NS, UK 22 Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark 23 California Institute of Technology, Department of Astrophysics, Pasadena, CA 91125, USA 24 Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA 91109, USA 25 Department of Physics, Southern Connecticut State University, New Haven, CT 06515, USA 26 Department of Physics and Astronomy, San Jose State University, San Jose, CA 95192, USA 27 Lowell Observatory, Flagstaff, AZ 86001, USA 28 Astronomy Department, University of Washington, Seattle, WA 94065, USA 29 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85726, USA 30 Laboratoire d’Astrophysique de Toulouse-Tarbes, Universite´ de Toulouse, CNRS, 31400 Toulouse, France 31 LESIA, CNRS, Universite´ Pierre et Marie Curie, Universite´ Denis Diderot, Observatoire de Paris, 92195 Meudon cedex, France 32 Orbital Sciences Corporation, NASA Ames Research Center, Moffett Field, CA 94035, USA 33 Bay Area Environmental Research Inst., NASA Ames Research Center, Moffett Field, CA 94035, USA 34 Steward Observatory, University of Arizona, Tucson, AZ 85726, USA 35 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark Received 2011 September 8; accepted 2011 November 21; published 2012 January 31 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 REarth 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 and 1.86 ± 0.04 R, 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 REarth 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 MEarth (2σ). HD 179070 is the brightest exoplanet host star yet discovered by Kepler. Key words: planetary systems – stars: activity – stars: individual (HD 179070: KIC 3632418) – stars: interiors – stars: late-type – stars: magnetic field – stars: oscillations (including pulsations) – techniques: photometric 1 The Astrophysical Journal, 746:123 (18pp), 2012 February 20 Howell et al. 1. INTRODUCTION 2. KEPLER OBSERVATIONS 2.1. Kepler Photometry The NASA Kepler mission, described in Borucki et al. (2010a), surveys a large area of the sky spanning the boundary The Kepler mission and its photometric performance since its of the constellations Cygnus and Lyra. The prime mission goal launch are described in Borucki et al. (2010a) while the CCD is to detect transits by exoplanets as their orbits allow them imager on board Kepler is described in Koch et al. (2010a) to pass in front of their parent star as viewed from the Earth. and van Cleve (2008). The Kepler observations of HD 179070 Exoplanets, both large and small and orbiting bright and faint used herein consist of data covering a time period of 460 days stars, have already been detected by the Kepler mission (see or Kepler observation Quarters 0 through 5 (JD 2,454,955 to Borucki et al. 2010b; Koch et al. 2010b; Batalha et al. 2010; 2,455,365). The photometric observations were reduced using Latham et al. 2010; Dunham et al. 2010; Jenkins et al. 2010a; the Kepler mission data pipeline (Jenkins et al. 2010b) and then Holman et al. 2010;Torresetal.2011;Howelletal.2010; passed through various consistency checks and exoplanet transit Lissauer et al. 2011) and many more exoplanet candidates are detection software as described in Van Cleve (2009) and Batalha known (Borucki et al. 2011). et al. (2011). Details of the Kepler light curves and the transit We report herein on one of the brightest targets in the Kepler model fitting procedures can be found in Howell et al. (2010), field, HD 179070 (KIC 3632418, KOI 975). This V = 8.3 Batalha et al. (2011), and Rowe et al. (2006). F6IV star has been observed prior to the Kepler mission as The top panel of Figure 1 shows the raw Kepler light curve a matter of course for essentially all of the Henry Draper of HD 179070 where the larger, low-frequency modulations do catalog stars. Catalog information37 for HD 179070 provides not likely represent real changes in the star. Thermal jumps in a Teff of 6137 K (spectral type F6 IV), a Hipparcos distance the focal plane temperature near days 100, 120, and 370 are of 108 ± 10 pc, [Fe/H] =−0.15, an age of 2.8 Gyr, a radial apparent (see Van Cleve 2009) due to safeing events in Q2 and − velocity (RV) of −28 km s 1, and E(b − y) = 0.011 mag. The Q5. Normalized and phase-folded light curves are produced and age, metallicity, and color excess reported in the catalog come the transit event in the phased light curve is modeled in an effort from the photometric study by Nordstrom¨ et al. (2004). Nothing to understand the transiting object. The middle panel of Figure 1 special distinguishes it from any other stars in the HD catalog. shows a blow-up (as highlighted in yellow) of a section of the HD 179070 is strongly saturated in the Kepler observations. raw light curve and represents a typical normalized result. The Techniques to obtain good photometry from saturated stars dotted lines mark the individual transit events and the entire are employed by the Kepler project and have been used to Kepler light curve shown here contains 164 individual transits. analyze light curves of other Kepler saturated stars (e.g., Welsh Taking random quarters of the total light curve and binning them et al. 2011). While a star will saturate the CCD detectors on on the transit period provide consistent results as shown in the Kepler if brighter than V ∼ R ∼ 11.5, collecting all the bottom panel of Figure 1 albeit of lower signal-to-noise ratio pixels which contain the starlight, including the bleed trail, (S/N). The bottom panel (Figure 1) shows the entire phase- allows a photometric study to be performed (see Gilliland folded light curve after detrending and binning all available et al. 2010). Kepler light curves of HD 179070 from the data.

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