| Abstract
| - 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 fits to stellar models to determine extinction individually for the stars in OB associations in these fields. The range of extinction within each cluster is the major constraint on our ability to determine accurate parameters for each association. We are able to determine ages of the clusters to ∼0.2 in log age, which is sufficient to distinguish between the older and younger associations. These observations provide us with the first measurement of the ages of young star clouds in M31 and allow us to make comparisons with other, less well-calibrated tracers of the association ages, in particular the Ha and H i morphologies.
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