T. R. Bedding, D. Huber, D. Stello, Y. Elsworth, S. Hekker, T. Kallinger, S. Mathur, B. Mosser, H. L. Preston, J. Ballot, C. Barban, A.-M. Broomhall, D. L. Buzasi, W. J. Chaplin, R. A. García, M. Gruberbauer, S. J. Hale, J. De Ridder, S. Frandsen, W. J. Borucki, T. M. Brown, J. Christensen-Dalsgaard, R. L. Gilliland, J. M. Jenkins, H. Kjeldsen, D. Koch, K. Belkacem, L. Bildsten, H. Bruntt, T. L. Campante, S. Deheuvels, A. Derekas, M.-A. Dupret, M.-J. Goupil, A. Hatzes, G. Houdek, M. J. Ireland, C. Jiang, C. Karoff, L. L. Kiss, Y. Lebreton, A. Miglio, J. Montalbán, A. Noels, I. W. Roxburgh, V. Sangaralingam, I. R. Stevens, M. D. Suran, N. J. Tarrant, A. Weiss

Abstract
We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30-minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (Δν) and the frequency of maximum power (ν_max). We focus on a sample of 50 low-luminosity stars (ν_max > 100 µHz, L ≲ 30 L_☉) having high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star-formation rate in the local disk. We use a new technique to compare stars on a single échelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l = 3. Measuring the small separation between l = 0 and l = 2 allows us to plot the so-called C-D diagram of δν₀₂ versus δν. The small separation δν₀₁ of l = 1 from the midpoint of adjacent l = 0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l = 1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants.

Keywords
stars: oscillations

The Astrophysical Journal Letters
Volume 713, Number 2, Page L_176
2010 March

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