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M. Blackburn (West Virginia University), E. Rubenstein (Yale University)
Until recently, no dwarf novae have been found in globular clusters (Paresce & de Marchi, 1994). Tidal theory predicts the presence of many such binary stars, yet there is no evidence that this is a real process. Most stars form in binaries in the field, and it is expected that stars form the same way in globular clusters. Previous studies have found the binary fraction to be between 15 inner core. Dwarf novae are detectable because of their relatively short recurrence times, ranging from 20 to 300 days, as compared with the 10,000 (or more) year recurrence times of classical novae. Dwarf novae also have amplitude outbursts of 2-6 in magnitude, making them potentially detectable. 47 Tucanae has been chosen for observation, as it appears in the right location at the right time of year, and its moderately metal poor population is known to have many millisecond pulsars and therefore is assumed to have a high binary fraction. The composition is useful in that it serves as a bridge between extreme metal poor stars and solar composition. This helps minimize any difference in metallicity of the dwarf novae, while still allowing for study of these differences.
Data obtained over a period of five months from the 1m YALO telescope at Cerro Tololo Inter-American Observatory has been reduced and averaged. The average image has been subtracted from each individual image to make moderate amounts of residual radiation apparent. To date, several variable stars have been found through visual means, but no dwarf novae. Further analysis of this data, as well as new data, may provide a more optimistic outcome. If found, we plan to derive limits on their frequency from our data set after performing artificial star tests, and to provide a clearer look at the stellar dynamics of globular clusters.
I'd like to thank NSF for the funding of this project.