Late-Type Stars in an Inner and Far Disk Field of M31

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 CM 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 fiels are much wider than can be accounted for by photometric errors. The distance to M31 is also determined using the carbon stars. A true distance modulus of 24.45 is found. 33 refs.