Imaging of the Stellar Population of IC 10 with Laser Guide Star Adaptive Optics and theHubble Space Telescope

We present adaptive optics (AO) images of the central starburst region of thedwarf irregular galaxy IC10. The Keck 2 telescope laser guide star was used toachieve near diffraction-limited performance at H and K' (Strehls of 18% and32%, respectively). The images are centered on the putative Wolf-Rayet (W-R)object [MAC92]24. We combine our AO images with F814W data from HST. Bycomparing the K' vs. [F814W]-K' color-magnitude diagram (CMD) with theoreticalisochrones, we find that the stellar population is best represented by at leasttwo bursts of star formation, one ~ 10 Myr ago and one much older (150-500Myr). Young, blue stars are concentrated in the vicinity of [MAC92]24. Thispopulation represents an OB association with a half-light radius of about 3 pc.We resolve the W-R object [MAC92]24 into at least six blue stars. Four of thesecomponents have near-IR colors and luminosities that make them robust WN starcandidates. By matching the location of C-stars in the CMD with those in theSMC we derive a distance modulus for IC10 of about 24.5 mag. and a foregroundreddening of E(B-V) = 0.95. We find a more precise distance by locating the tipof the giant branch in the F814W, H, and K' luminosity functions. We find aweighted mean distance modulus of 24.48 +/- 0.08. The systematic error in thismeasurement, due to a possible difference in the properties of the RGBpopulations in IC10 and the SMC, is +/- 0.16 mag.Comment: 13 pages, 13 figures, ApJ in pres