| Abstract | Using the 3.6 m Canada-France-Hawaii Telescope (CFHT), we have obtained B, V, and R CCD images of a large field in the nearby galaxy NGC 253, sampling portions of both the inner and outer disk regions (Scoville et al. 1985). The data were recorded during conditions of exceptionally good seeing, permitting individual stars to be resolved over a large area of the galaxy. Two-color and color-magnitude diagrams are constructed, and it appears that the majority of the stars we have detected are supergiants of spectral types A, F, and G. We find that (1) the difference in mean visual extinction between the inner and outer disk is ~1 magnitude; (2) the apparent brightnesses of the most luminous stars in the inner and outer disk regions are similar which, given the difference in mean extinction, suggests that the former area contains stars which are intrinsically brighter, and hence more massive, than in the latter; and (3) if A_v_ does not exceed ~2 magnitudes, the majority of the stars we have detected have masses less than or equal to 40 M_sun_. Finally, the luminosity functions in all three bandpasses of stars in the outer disk region follow power laws, with slopes similar to those seen in other spiral galaxies. The brightest red supergiants occur at V ~ 19.0 and, if these stars are similar to those in other nearby galaxies, then the distance modulus of NGC 253 is less than or equal to 27.0. |
