The Recent Evolution of the Dwarf Starburst Galaxy NGC 625 fromHubble Space TelescopeImaging

New HST/WFPC2 imaging of the dwarf starburst galaxy NGC 625 is presented.These data, 80% complete to V and I magnitudes of 26.0 and 25.3, respectively,allow us to study the recent star formation history of NGC 625. We derive a tipof the red giant branch (TRGB) distance modulus of 27.95+/-0.07, correspondingto a distance of 3.89+/-0.22 Mpc, and a location on the far side of theSculptor Group. NGC 625 has a well-defined radial stellar population gradient,evidenced by a central concentration of young MS stars and an RGB/AGB ratiothat increases with galactocentric distance. The prominent AGB is very red, andRGB stars are detected far from the central star forming regions. Using H Alphaand H Beta narrow band imaging and previous optical spectroscopy we identifysubstantial and varying internal extinction (A_V = 0.0 to 0.6 mag) associatedwith the central active star formation regions. To better understand theeffects of internal extinction on the analysis of young stellar populations,synthetic models are presented which, for the first time, examine and accountfor this effect. Using the luminous blue helium burning stars, we construct asimple model of the recent (< 100 Myr) star formation in which an elevated butdeclining star formation rate has been present over this entire period. This isat odds with the presence of spectroscopic W-R features in the major starformation region which imply a short duration (<= 5 Myr) for the recentstarburst. This suggests that starbursts displaying W-R features are notnecessarily all of a short duration. Finally, we speculate on the possiblecauses of the present burst of star formation in this apparently isolatedgalaxy, and compare it to other nearby, well-studied dwarf starburst systems.