Carbon Stars and Other Luminous Stellar Populations in M33

The M33 galaxy is a nearby, relatively metal-poor, late-type spiral. Its proximity and almost face-on inclination means that it projects over a large area on the sky, making it an ideal candidate for wide-field CCD mosaic imaging. Photometry was obtained for more than 10⁶ stars covering a 74^'×56^' field centered on M33. Main-sequence, supergiant branch, red giant branch, and asymptotic giant branch (AGB) populations are identified and classified based on broadband V and I photometry. Narrowband filters are used to measure spectral features allowing, the AGB population to be further divided into C and M star types. The galactic structure of M33 is examined using star counts, color-color-, and color-magnitude-selected stellar populations. We use the C to M star ratio to investigate the metallicity gradient in the disk of M33. The C/M star ratio is found to increase and then flatten with increasing galactocentric radius, in agreement with viscous disk formation models. The C star luminosity function is found to be similar to M31 and the SMC, suggesting that C stars should be useful distance indicators. The ``spectacular arcs of carbon stars'' in M33 postulated recently by Block et al. are found in our work to be simply an extension of M33's disk.