4 research outputs found
DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR Ξ CYG, THE BRIGHTEST STAR OBSERVED BY THE KEPLER MISSION
Ξ 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 ïŹrst obtained during Quarter 6 (2010 JuneâSeptember) and subsequently in Quarters 8 and 12â17. 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 1000â2700 ÎŒHz, a large frequency separation of 83.9 ± 0.4 ÎŒHz, and maximum oscillation amplitude at frequency Îœmax = 1829 ± 54 ÎŒHz. 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 Re, [Fe/H] = â0.02 ± 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-ïŹt models have masses of 1.35â1.39 Me and ages of 1.0â1.6 Gyr. Ξ Cygâs Teff and log g place it cooler than the red edge of the Îł Doradus instability region established from pre-Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show Îł Dor gravity modes driven by the
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convective blocking mechanism, with frequencies of 1â3 cycles per day (11 to 33 ÎŒHz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 ÎŒHz) may be attributable to a faint, possibly background, binary