Studies of luminous stars in nearby galaxies. IV. Baade's field IV in M 31.

The spectra and luminosities of the brightest stars, the color-magnitude diagrams, the ages and dimensions of the associations, and even the ratio of blue to red supergiants in Baade's Field IV in the outer parts of M 31 are all very similar to those observed in the spiral features in our region of the Milky Way. These observations suggest that the stellar evolution of the Population I members of M 31 is very similar to that of the spiral arm population in the Galaxy, although the results apply to only one small region in one spiral feature. Further studies of the stellar content of other M 31 regions may reveal differences.