학술논문
Detection of Solar-Like Oscillations, Observational Constraints, and Stellar Models for $\theta$ Cyg, the Brightest Star Observed by the {\it Kepler} Mission
Document Type
Working Paper
Author
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.; Pápics, P. I.; White, T. R.; Aerts, C.; Ballot, J.; Boyajian, T. S.; Briquet, M.; Bruntt, H.; Buchhave, L. A.; Campante, T. L.; Catanzaro, G.; Christensen-Dalsgaard, J.; Davies, G. R.; Doğan, G.; Dragomir, D.; Doyle, A. P.; Elsworth, Y.; Frasca, A.; Gaulme, P.; Gruberbauer, M.; Handberg, R.; Hekker, S.; Karoff, C.; Lehmann, H.; Mathias, P.; Mathur, S.; Miglio, A.; Molenda-Żakowicz, J.; Mosser, B.; Murphy, S. J.; Régulo, C.; Ripepi, V.; Salabert, D.; Sousa, S. G.; Stello, D.; Uytterhoeven, K.
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Subject
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Abstract
$\theta$ 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.
Comment: Accepted for Publication in The Astrophysical Journal, July 1, 2016
Comment: Accepted for Publication in The Astrophysical Journal, July 1, 2016