M31 UBVR photometry

The color-magnitude diagram shows a main sequence that reaches from Mv=-0.7 (at our photometric limit) to Mv=-6.2 and a well-populated giant region. The R, B-R diagram separates the stars rather clearly into three groups, the main sequence, intermediate-color stars (which include the brighter foreground stars), and the red giants.

Reddening is found to average E(B-V)=0.13+/-0.04. To determine a reliable luminosity function, we have eliminated foreground contamination and have evaluated our sample completeness, using a large number of artificial stars in the DAOPHOT reduction routine. The corrected luminosity function, which extends from Mv=-5 to -1, has a logarithmic slope of 0.57+/-0.07 for all stars and 0.53+/-0.06 for main-sequence stars only.