The Metallicity Distribution in the Outer Halo of M33
  We present the results of deep I and V-band photometry of the halo stars near the southeast minor axis of the Local Group spiral galaxy M33. An (I,V-I) color-magnitude diagram distinctly reveals the red giant branch stars at the bright end of the color-magnitude diagram. A luminosity function in the I-band which utilizes a background field to remove the contaminating effects of Galactic foreground stars and distant, unresolved galaxies reveals the presence of the tip of the red giant branch at (m-M)_{I}=20.70. Assuming an absolute magnitude of the tip of the red giant branch of M_{I,TRGB}=-4.1 and a foreground reddening of E(V-I)=0.054, the distance modulus of M33 is determined to be (m-M)=24.72 (880 kpc). The metallicity distribution function derived by interpolating between evolutionary tracks of red giant branch models is dominated by a relatively metal poor stellar population, with a mean metallicity of [m/H]=-0.94 or [Fe/H]=-1.24. We fit a leaky-box chemical enrichment model to the halo data, which shows that the halo is well represented by a single-component model with an effective yield of y_{eff}=0.0024. 
R. Scott Brooks, Christine D. Wilson, William E. Harris