Three-Color Photometry in the Globular Cluster M3.

New three-color photometric data are presented for about 225 stars in the globular cluster M3. These stars permit conversion of the older mpg, m magnitude in M3 to the well-defined B, V system. A new color-magnitude diagram in V and B - V is given. An ultraviolet excess exists for the giant, subgiant, and main-sequence stars. This excess ranges from about A(U - B) = 0.20 mag. for the giants at B - V = 1.0 to A(U - B) = 0.55 mag. for main-sequence stars at B - V = 0.6. As in M13, the M3 stars along the blue-end horizontal branch appear to have an ultraviolet deficiency which may be due to the effect of low surface gravity on the Balmer jump. The difference in the energy distributions for the M3 stars compared with the nearby stars makes any identification of sequences dubious at this time.