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Centro de Astrofísica da Universidade do Porto

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

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

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.

asteroseismology, stars: fundamental parameters, stars: interiors, stars: solar-type

The Astrophysical Journal
Volume 831
October 2016

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Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

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