Gilliland, R. L.; Brown, T. M.; Kjeldsen, H.; McCarthy, J. K.; Peri, M. L.; Belmonte, J. A.; Vidal, I.; Cram, L. E.; Palmer, J.; Frandsen, S.; Parthasarathy, M.; Petro, L.; Schneider, H.; Stetson, P. B.; Weiss, W. W.
Bibliographical reference
The Astronomical Journal (ISSN 0004-6256), vol. 106, no. 6, p. 2441-2476
Advertised on:
12
1993
Citations
120
Refereed citations
93
Description
Results are presented from a large observational project directed toward
the detection of solar-like oscillations in an ensemble of open cluster
stars. Seven groups collaborated in 1992 January to observe twelve stars
in M67 with 4 m class telescopes for a one week period. High quality
time series were collected on 22 telescope nights for a total of 156 h.
The technique of CCD ensemble photometry allowed precisions of about 250
micro-mag per minute to be reached in the best cases, and provided
robust results in conditions that sometimes were far from 'photometric.'
The longitude-distributed network, coupled with generally low noise
levels, provided a good window function and yielded detection thresholds
of about 20 micro-mag (five times solar) for solar-like oscillations in
the best ensembled stars. Sensitivity to solar-like oscillations over
our twelve ensemble stars ranges from 30% to a factor of three better
than obtained previously by any group. When our simulations results for
12 stars is taken into account this project provides a (multiplexed)
factor of 20 to 30 gain over previous experiments. For two stars we
derive interesting upper limits for oscillation amplitudes that are near
the lower range predicted by theory. Over half the stars in the ensemble
show suggestive evidence for oscillations; we develop the evidence for,
and the cautions against, claiming detections in these cases. We argue
that a more aggressive network campaign could provide a factor of two
sensitivity gain with a resulting high probability of attaining
unambiguous oscillation detections on most of the stars in the M67
ensemble.