  Scaling relations that link asteroseismic quantities to global stellar
properties are important for gaining understanding of the intricate physics
that underpins stellar pulsation. The common notion that all stars in an open
cluster have essentially the same distance, age, and initial composition,
implies that the stellar parameters can be measured to much higher precision
than what is usually achievable for single stars. This makes clusters ideal for
exploring the relation between the mode amplitude of solar-like oscillations
and the global stellar properties. We have analyzed data obtained with NASA's
Kepler space telescope to study solar-like oscillations in 100 red giant stars
located in either of the three open clusters, NGC 6791, NGC 6819, and NGC 6811.
By fitting the measured amplitudes to predictions from simple scaling relations
that depend on luminosity, mass, and effective temperature, we find that the
data cannot be described by any power of the luminosity-to-mass ratio as
previously assumed. As a result we provide a new improved empirical relation
which treats luminosity and mass separately. This relation turns out to also
work remarkably well for main-sequence and subgiant stars. In addition, the
measured amplitudes reveal the potential presence of a number of previously
unknown unresolved binaries in the red clump in NGC 6791 and NGC 6819, pointing
to an interesting new application for asteroseismology as a probe into the
formation history of open clusters.
