| Abstract | Two disk fields in M31, one in Baade's field IV at 20 kpc from the nucleus of the galaxy and the other at 4 kpc, were surveyed for late-type stars using broad-band V and I filters (both fields) as well as narrow-band filters in the outer field. The carbon to late M star ratio in the outer field was found to be 0.15, almost identical to that in a field at 11 kpc studied earlier. The color-magnitude diagrams for both fields were constructed. The diagram for the outer field clearly shows a giant branch which extends well to the red of that of the most metal-rich globular cluster. The carbon stars occupy a relatively unique position in this diagram, being in general the most luminous objects in the field. The widths of the giant branches in both fields are much wider than can be accounted for by photometric errors. The most likely reason for this in the outer field is that stars with a range in mass of about a factor of 2 are funneling into this region of the color-magnitude diagram. Asymptotic giant branch (AGB) luminosity functions were assembled for the inner and outer fields and compared with that for a field at 11 kpc studied in an earlier paper. The functions in the outer two fields are identical within the errors, but the inner field exhibits a lack of luminous AGB stars together with an excess of faint ones. Finally, the distance to M31 is determined using the carbon stars. A true distance modulus of 24.45 is found. |
