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Session 80 - Star Clusters in the Milky Way.
Display session, Friday, January 09
Exhibit Hall,
We have begun a program to monitor several thousand open cluster stars simultaneously in a search for small amplitude variable stars. Our targets are the well-known old open clusters, NGC 188, M67, NGC 6819 and NGC 7789, using the University of Illinois 1-meter telescope at the Mt. Laguna Observatory,
Among the phenomena we hope to uncover are short-period eclipsing systems, reflection effects in close, but non-eclipsing systems, \delta\ Scuti stars and indicators of stellar activity (starspots). In an initial analysis of our data for NGC 7789, we have recovered almost all the known and suspected variables, as well as at least one previously undetected eclipsing system and several other possible variables. A key consideration for the present project is the limiting precision of differential photometry. We find that the errors are dominated by Poisson statistics, with differential magnitude errors of well-exposed stars, averaged over several nights of observations, as low as \pm0.0030 mag.\ per three-minute (V) exposure. Summary information and light curves will be presented for the variables found to date.
