SCYON Abstract

Received on February 22 2007

Multisite campaign on the open cluster M67. II. Evidence for solar-like oscillations in red giant stars

AuthorsD. Stello (1,2,3), H. Bruntt (1,2,3), H. Kjeldsen (1,4), T.R. Bedding (2), T. Arentoft (1,2,4), R.L. Gilliland (5), J. Nuspl (6), S.-L. Kim (7), Y.B. Kang (7), J.-R. Koo (7), J.-A. Lee (7), C. Sterken (8), C.-U. Lee (7), H.R. Jensen (1), A.P. Jacob (2), R. Szabó (9,6), S. Frandsen (1,4), Z. Csubry (6), Z.E. Dind (2), M.Y. Bouzid (8), T.H. Dall (10) and L.L. Kiss (2)
(1) Institut for Fysik og Astronomi (IFA), Aarhus Universitet, 8000 Aarhus, Denmark
(2) School of Physics, University of Sydney, NSW 2006, Australia
(3) Department of Physics, US Air Force Academy, Colorado Springs, CO80840, USA
(4) Danish AsteroSeismology Centre, Aarhus Universitet, DK-8000 Aarhus, Denmark
(5) Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, USA
(6) Konkoly Observatory of the Hungarian Academy of Sciences, H-1525 Budapest, PO Box 67, Hungary
(7) Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea
(8) Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
(9) Physics Department, University of Florida, Gainesville, FL, 32611, USA
(10) European Southern Observatory, Casilla 19001, Santiago 19, Chile
Accepted byMonthly Notices of the Royal Astronomical Society
Links M67


Measuring solar-like oscillations in an ensemble of stars in a cluster, holds promise for testing stellar structure and evolution more stringently than just fitting parameters to single field stars. The most ambitious attempt to pursue these prospects was by (Gilliland 1993) who targeted 11 turn-off stars in the open cluster M67 (NGC 2682), but the oscillation amplitudes were too small (< 20 µmag) to obtain unambiguous detections. Like Gilliland (1993) we also aim at detecting solar-like oscillations in M67, but we target red giant stars with expected amplitudes in the range 50-500 µmag and periods of 1 to 8 hours. We analyse our recently published photometry measurements, obtained during a six-week multisite campaign using nine telescopes around the world. The observations are compared with simulations and with estimated properties of the stellar oscillations. Noise levels in the Fourier spectra as low as 27 µmag are obtained for single sites, while the combined data reach 19micromag, making this the best photometric time series of an ensemble of red giant stars. These data enable us to make the first test of the scaling relations (used to estimate frequency and amplitude) with an homogeneous ensemble of stars. The detected excess power is consistent with the expected signal from stellar oscillations, both in terms of its frequency range and amplitude. However, our results are limited by apparent high levels of non-white noise, which cannot be clearly separated from the stellar signal.