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Huber Daniel, Bedding Timothy R., Stello Dennis, Mosser Benoît, Mathur Savita, Kallinger Thomas, Hekker Saskia, Elsworth Yvonne P., Buzasi D. L., De Ridder Joris, Gilliland Ronald L., Kjeldsen Hans, Chaplin William J., Garcia Rafael A., Hale S. J., Preston H. L., White Timothy R., Borucki William J., Christensen-Dalsgaard Jörgen, Clarke B. D., Jenkins Jon M., Koch David

Asteroseismology of Red Giants from the First Four Months of Kepler Data: Global Oscillation Parameters for 800 Stars

The Astrophysical Journal, 2010, vol. 723, pp. 1607-1617

Référence DOI : 10.1088/0004-637X/723/2/1607
Référence ADS : 2010ApJ...723.1607H

Résumé :

We have studied solar-like oscillations in ~800 red giant stars using Kepler long-cadence photometry. The sample includes stars ranging in evolution from the lower part of the red giant branch to the helium main sequence. We investigate the relation between the large frequency separation (Deltanu) and the frequency of maximum power (nu<SUB>max</SUB>) and show that it is different for red giants than for main-sequence stars, which is consistent with evolutionary models and scaling relations. The distributions of nu<SUB>max</SUB> and Deltanu are in qualitative agreement with a simple stellar population model of the Kepler field, including the first evidence for a secondary clump population characterized by M >~ 2 M <SUB>sun</SUB> and nu<SUB>max</SUB> ~= 40-110 muHz. We measured the small frequency separations deltanu<SUB>02</SUB> and deltanu<SUB>01</SUB> in over 400 stars and deltanu<SUB>03</SUB> in over 40. We present C-D diagrams for l = 1, 2, and 3 and show that the frequency separation ratios deltanu<SUB>02</SUB>/Deltanu and deltanu<SUB>01</SUB>/Deltanu have opposite trends as a function of Deltanu. The data show a narrowing of the l = 1 ridge toward lower nu<SUB>max</SUB>, in agreement with models predicting more efficient mode trapping in stars with higher luminosity. We investigate the offset epsilon in the asymptotic relation and find a clear correlation with Deltanu, demonstrating that it is related to fundamental stellar parameters. Finally, we present the first amplitude-nu<SUB>max</SUB> relation for Kepler red giants. We observe a lack of low-amplitude stars for nu<SUB>max</SUB> >~ 110 muHz and find that, for a given nu<SUB>max</SUB> between 40 and 110 muHz, stars with lower Deltanu (and consequently higher mass) tend to show lower amplitudes than stars with higher Deltanu.

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