Stellar populations of the dwarf irregular galaxy WLM

We have obtained V-band photometry for 8000 stars, and I-band photometry for 16000 stars in the field of the dwarf irregular galaxy WLM, a member of the Local Group. From the VI color-magnitude diagram we infer metallicities and ages for the stellar populations in the main body and in the halo of WLM. The youngest stars in the galaxy have an age of similar to 10(7) Gyr. For the oldest stars we derive an age of > 10(10) Gyr and a metallicity of [Fe/H] = - 1.45 +/- 0.2. We construct a deep luminosity function, obtaining an accurate distance modulus m - M = 24.75 +/- 0.1 for this galaxy based on the I-magnitude of the RGB tip and adopting E(V - I) = 0.03. We establish the presence of an extended, slightly flattened halo consisting of Population II stars. Cluster D of Ables & Ables (1977, ApJS, 34, 245) is confirmed as the only globular cluster present in the main body of this galaxy. There are no other clusters brighter than I = 19.5. The B - V color gradient observed by Ables & Ables (1977) is shown to be caused by a stellar-population transition, and not a metallicity gradient or dust extinction. (C) 1997 American Astronomical Society.