STELLAR POPULATIONS OF THE DWARF IRREGULAR GALAXY WLM

We have obtained V-band photometry for 8000 stars, and I-band photomet ry for 16000 stars in the field of the dwarf irregular galaxy WLM, a m ember of the Local Group. From the VI color-magnitude diagram we infer metallicities and ages for the stellar populations in the main body a nd 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(1 0) Gyr and a metallicity of [Fe/H] = - 1.45 +/- 0.2. We construct a de ep 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 extende d, slightly flattened halo consisting of Population II stars. Cluster D of Ables & Ables (1977, ApJS, 34, 245) is confirmed as the only glob ular cluster present in the main body of this galaxy. There are no oth er 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) 199 7 American Astronomical Society.