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B. J. Pritzl, T. E. Armandroff (NOAO/KPNO), G. H. Jacoby (WIYN), G. S. Da Costa (RSAA/ANU)
Dwarf galaxies play an important role in the understanding of galaxy formation. The Galactic dwarf spheroidal companions have great diversity in their star formation histories. In general, they also have a range in metallicity among their stars. The diversity in the stellar populations is reflected in the variable star content of these systems. In addition, the variable stars provide independent distance estimates to the dwarf galaxies.
We present the results of a variable star search of the M31 dwarf spheroidal companion Andromeda VI using HST/WFC2 observations. 111 RR Lyrae and 6 anomalous Cepheids were found. The Andromeda VI anomalous Cepheids follow the period-luminosity relations as defined by those in Galactic systems. Through various methods we show the Andromeda VI RR Lyrae have on average the same mean metallicity as was previously found in the galaxy ([Fe/H]=-1.58) by Armandroff, Jacoby, and Davies (1999). They are also found to be consistent with those from Galactic globular clusters of similar metallicities in a period-amplitude diagram. We find the RR Lyrae distance to Andromeda VI to be 810 kpc, which compares very well with the value of 775±5 kpc derived by Armandroff et al. from the tip of the red giant branch.
This research is supported in part by NASA through grant number GO-08272 from the Space Telescope Science Institute.