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M. Pappas, A. Sarajedini (Wesleyan University), B. Chaboyer (Dartmouth College)
We present a V- and I-band study of the halo field population in the Local Group galaxy, M33. Images were taken with the Echelle T2KB CCD camera attached to the Michigan-Dartmouth-MIT (MDM) 2.4-m telescope. Six exposures were obtained in V and twelve exposures in I, giving a total exposure time of 7200 s and 10,000 s, respectively.
The purpose of this study is to obtain accurate information on the mean metallicity and metallicity spread of the halo field as well as determining the distance to M33. This was done by performing photometry on the images through the application of the DAOPHOT point-spread function algorithm. Based on these reductions, a color-magnitude diagram in the VI passbands is constructed and analyzed. Using the concept that the absolute I magnitude of the RGB tip (TRGB) is constant, the distance to M33 using the TRGB of the halo population is determined. The mean dereddened color of the red-giant branch (RGB) provides an estimate of the mean metallicity of the halo population. Finally, the metallicity dispersion is determined by measuring the width of the RGB, after accounting for the photometric errors through artificial star experiments.