We present UBV color-magnitude diagrams (CMDs) for the globular cluster M4. The CMDs show a sequence of four luminous blue stars (V<20, U-V<-0.6), which appear to be cluster hot subdwarfs. We present spectra for the three brightest ones. We also note the presence of a population of faint blue objects, likely to be hot, young white dwarfs belonging to the cluster. We have selected five objects above V=22mag, bright enough for follow-up ground-based spectroscopy, and present their coordinates and finding charts. We show a spectrum for variable V46, which suggests that it is a hot subdwarf, along with a new light curve obtained with the ISIS image subtraction package. The light curve is unstable, but only one period of variability is apparent. Two new variables have been discovered, both located on the cluster red giant branch. We also present a differential E(B-V) reddening map and a fiducial sequence for the main sequence, subgiant branch, and red giant branch on the V/B-V CMD for a selected region with uniform reddening. Based on a comparison with the M5 fiducial sequence, we obtain a reddening estimate of E(B-V)=0.41mag toward M4, consistent with previous determinations.

Cone search capability for table J/AJ/124/1486/m4wd (UBV photometry and astrometry of the white dwarfs)

Cone search capability for table J/AJ/124/1486/m4ubv (Astrometry and UBV photometry for 12121 stars in M4)