Detection of Solar-Like Oscillations, Observational Constraints, and Stellar Models for Θ Cyg, the Brightest Star Observed by the Kepler Mission

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 T eff = 6697±78 K, radius 1.49±0.03 R e , [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 e 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

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“…Therefore, we only considered the radial orders for the even-and odd-degree centroids where the l=0 and l=1 modes, respectively, were measured by their respective sources. For example, Guzik et al (2016) reported 39 radial and dipole modes in θ Cyg, therefore we extracted 39 centroid frequencies from the power spectrum.…”

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