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Register a new userSolar-like oscillations in open cluster stars
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Asteroseismology of stellar clusters is potentially a powerful tool. The assumption of a common age, distance, and chemical composition provides constraints on each cluster member, which significantly improves the asteroseismic output. Driven by this great potential, we carried out multi-site observations aimed at detecting solar-like oscillations in the red giant stars in the open cluster M67 (NGC 2682) (Stello et al. 2006). Here we present the first analysis of our data, which show evidence of excess power in the Fourier spectra, shifting to lower frequencies for more luminous stars, consistent with expectations from oscillations. If the observed power excesses were due to stellar oscillations, this result would show great prospects for asteroseismology in stellar clusters.
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We present a brief overview of the history of attempts to obtain a clear detection of solar-like oscillations in cluster stars, and discuss the results on the first clear detection, which was made by the Kepler Asteroseismic Science Consortium (KASC) Working Group 2.
Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819 -- one of four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation and the frequency of maximum oscillation power. We find that the asteroseismic parameters allow us to test cluster-membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about two orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler.
The Hyades open cluster was targeted during Campaign 4 (C4) of the NASA K2 mission, and short-cadence data were collected on a number of cool main-sequence stars. Here, we report results on two F-type stars that show detectable oscillations of a quality that allows asteroseismic analyses to be performed. These are the first ever detections of solar-like oscillations in main-sequence stars in an open cluster.
The F5 subgiant Procyon A (alpha CMi, HR 2943) was observed with the Coralie fiber-fed echelle spectrograph on the 1.2-m Swiss telescope at La Silla in February 1999. The resulting 908 high-accuracy radial velocities exhibit a mean noise level in the amplitude spectrum of 0.11 m s^-1 at high frequency. These measurements show significant excess in the power spectrum between 0.6-1.6 mHz with 0.60 m s^-1 peak amplitude. An average large spacing of 55.5 uHz has been determined and twenty-three individual frequencies have been identified.
We have observed evidence for $p$-mode oscillations in the G0 IV star etaBoo (V = 2.68). This represents the first clear evidence of solar-like oscillations in a star other than the Sun. We used a new technique which measures fluctuations in the temperature of the star via their effect on the equivalent widths of the Balmer lines. The observations were obtained over six nights with the 2.5 m Nordic Optical Telescope on La Palma and consist of 12684 low-dispersion spectra. In the power spectrum of the equivalent-width measurements, we find an excess of power at frequencies around 850 microHz (period 20 minutes) which consists of a regular series of peaks with a spacing of $Delta u=40.3$ microHz. We identify thirteen oscillation modes, with frequency separations in agreement with theoretical expectations. Similar observations of the daytime sky show the five-minute solar oscillations at the expected frequencies.
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