WHITE-DWARFS IN GLOBULAR-CLUSTERS - HUBBLE-SPACE-TELESCOPE OBSERVATIONS OF M4

Using WFPC2 on the Hubble Space Telescope, we have isolated a sample o f 258 white dwarfs (WDs) in the Galactic globular cluster M4. Fields a t three radial distances from the cluster center were observed, and si zable WD populations were found in all three. The location of these WD s in the color-magnitude diagram, their mean mass of 0.51(+/-0.03) M., and their luminosity function confirm basic tenets of stellar evoluti on theory and support the results from current WD cooling theory. The WDs are used to extend the cluster main-sequence mass function upward to stars that have already completed their nuclear evolution. The WD/r ed dwarf binary frequency in M4 is investigated and is found to be at most a few percent of all the main-sequence stars. The most ancient WD s found are similar to 9 Gyr old, a level that is set solely by the ph otometric limits of our data. Even though this is less than the age of M4, we discuss how these cooling WDs can eventually be used to check the turnoff ages of globular clusters and hence constrain the age of t he universe.