Article, Preprint OPEN
Guzik, J.A. ; Houdek, G. ; Chaplin, W.J. ; Smalley, B. ; Kurtz, D.W. ; Gilliland, R.L. ; Mullally, F. ; Rowe, J.F. ; Bryson, S.T. ; Still, M.D. ; Antoci, V. ; Appourchaux, T. ; Basu, S. ; Bedding, T.R. ; Benomar, O. ; Garcia, R.A. ; Huber, D. ; Kjeldsen, H. ; Latham, D.W. ; Metcalfe, T.S. ; Papics, P.I. ; White, T.R. ; Aerts, C. ; Ballot, J. ; Boyajian, T.S. ; Briquet, M. ; Bruntt, H. ; Buchhave, L.A. ; Campante, T.L. ; Catanzaro, G. ... view all 55 authors (2016)
  • Publisher: American Astronomical Society
  • Related identifiers: doi: 10.3847/0004-637X/831/1/17
  • Subject: Astrophysics - Solar and Stellar Astrophysics | F500 | QB | asteroseismology | solar-type [stars] | interiors [stars] | fundamental parameters [stars]

$\theta$ Cygni is an F3 spectral-type main-sequence star with visual magnitude V=4.48. This star was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were obtained during Quarter 6 (June-September 2010) and subsequently in Quarters 8 and 12-17. We present analyses of the solar-like oscillations based on Q6 and Q8 data, identifying angular degree $l$ = 0, 1, and 2 oscillations in the range 1000-2700 microHz, with a large frequency separation of 83.9 plus/minus 0.4 microHz, and frequency with maximum amplitude 1829 plus/minus 54 microHz. We also present analyses of new ground-based spectroscopic observations, which, when combined with angular diameter measurements from interferometry and Hipparcos parallax, give T_eff = 6697 plus/minus 78 K, radius 1.49 plus/minus 0.03 solar radii, [Fe/H] = -0.02 plus/minus 0.06 dex, and log g = 4.23 plus/minus 0.03. We calculate stellar models matching the constraints using several methods, including using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses 1.35-1.39 solar masses and ages 1.0-1.6 Gyr. theta Cyg's T_eff and log g place it cooler than the red edge of the gamma Doradus instability region established from pre-Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show gamma Dor gravity-mode pulsations driven by the convective-blocking mechanism, with frequencies of 1 to 3 cycles/day (11 to 33 microHz). However, gravity modes were not detected in the Kepler data, one signal at 1.776 cycles/day (20.56 microHz) may be attributable to a faint, possibly background, binary. Asteroseismic studies of theta Cyg and other A-F stars observed by Kepler and CoRoT, will help to improve stellar model physics and to test pulsation driving mechanisms.
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