Detection of Solar-like Oscillations, Observational Constraints, and Stellar Models for θ Cyg, the Brightest Star Observed By the Kepler Mission

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.

Detection of Solar-like Oscillations, Observational Constraints, and Stellar Models for θ Cyg, the Brightest Star Observed By the Kepler Mission,
The Astrophysical Journal, Vol. 831, Issue 1


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 T eff = 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

Leave a Reply

Your email address will not be published. Required fields are marked *