HUBBLE-SPACE-TELESCOPE OBSERVATIONS OF M31 ASSOCIATIONS

We have used HST WFPC-2 observations of five fields along the eastern spiral arm regions of M31 to study the stellar populations, We use fit s to stellar models to determine extinction individually for the stars in OB associations in these fields, The range of extinction within ea ch cluster is the major constraint on our ability to determine accurat e parameters for each association, We are able to determine ages of th e clusters to similar to 0.2 in log age, which is sufficient to distin guish between the older and younger associations, These observations p rovide us with the first measurement of the ages of young star clouds in M31 and allow us to make comparisons with other, less well-calibrat ed tracers of the association ages, in particular the H alpha and Hr m orphologies.