J. A. Guzik, G. Houdek, W. J. Chaplin, B. Smalley, D. W. Kurtz, R. L. Gilliland, F. Mullally, J. F. Rowe, S. T. Bryson, M. Still, V. Antoci, T. Appourchaux, S. Basu, T. R. Bedding, O. Benomar, R. Garcia, D. Huber, H. Kjeldsen, D. W. Latham, T. S. Metcalfe, P. I. Pápics, T. R. White, C. Aerts, J. Ballot, T. S. Boyajian, M. Briquet, H. Bruntt, L. A. Buchhave, T. L. Campante, G. Catanzaro, J. Christensen-Dalsgaard, G. R. Davies, G. Doǧan, D. Dragomir, A. P. Doyle, Y. Elsworth, A. Frasca, P. Gaulme, M. Gruberbauer, R. Handberg, S. Hekker, H. Lehmann, P. Mathias, S. Mathur, A. Miglio, J. Molenda-Żakowicz, B. Mosser, S. J. Murphy, C. Régulo, V. Ripepi, D. Salabert, S. G. Sousa, D. Stello, K. Uytterhoeven
Abstract
θ Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star that was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were first obtained during Quarter 6 (2010 June-September) and subsequently in Quarters 8 and 12-17. We present analyses of solar-like oscillations based on Q6 and Q8 data, identifying angular degree l = 0, 1, and 2 modes with frequencies of 1000-2700 μHz, a large frequency separation of 83.9 ± 0.4 μHz, and maximum oscillation amplitude at frequency ν max = 1829 ± 54 μHz. We also present analyses of new ground-based spectroscopic observations, which, combined with interferometric angular diameter measurements, give Teff = 6697 ± 78 K, radius 1.49 ± 0.03 R☉, [Fe/H] = -0.02 ± 0.06 dex, and log g = 4.23 ± 0.03. We calculate stellar models matching these constraints using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses of 1.35-1.39 M☉ and ages of 1.0-1.6 Gyr. θ Cyg’s T eff and log g place it cooler than the red edge of the γ Doradus instability region established from pre-Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show γ Dor gravity modes driven by the convective blocking mechanism, with frequencies of 1-3 cycles per day (11 to 33 μHz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 μHz) may be attributable to a faint, possibly background, binary.
Keywords
asteroseismology, stars: fundamental parameters, stars: interiors, stars: solar-type
The Astrophysical Journal
Volume 831, Number 1
2016 November
