Solar-like oscillations in low-luminosity red giants: first results from Kepler
Bedding, T. R; Huber, D; Stello, D; Elsworth, Y. P; Hekker, S; Kallinger, T; Mathur, S; Mosser, B; Preston, H. L; Ballot, J; Barban, C; Broomhall, A. M; Buzasi, D. L; Chaplin, W. J; Garcia, R. A; Gruberbauer, M; Hale, S. J; De Ridder, J; Frandsen, S; Borucki, W. J; Brown, T; Christensen-Dalsgaard, J; Gilliland, R. L; Jenkins, J. M; Kjeldsen, H; Koch, D; Belkacem, K; Bildsten, L; Bruntt, H; Campante, T. L; Deheuvels, S; Derekas, A; Dupret, M. A; Goupil, M. J; Hatzes, A; Houdek, G; Ireland, M. J; Jiang, C; Karoff, C; Kiss, L. L; Lebreton, Y; Miglio, A; Montalban, J; Noels, A; Roxburgh, I. W; Sangaralingam, V; Stevens, I. R; Suran, M. D; Tarrant, N. J; Weiss, A
Date:
2010-04
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 (Delta nu) and the frequency of maximum power (nu_max). We focus on a sample of 50 low-luminosity stars (nu_max > 100 muHz, L <~ 30 L_sun) 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 echelle 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 delta nu_02 versus Delta nu. The small separation delta nu_01 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.
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