| Abstract | Deep VI CCD photometry of ~4200 stars in a 3.9' x 3.9' central field of NGC 3109, a bright Magellanic-type spiral galaxy (Sm IV), has been obtained. The tip of the red giant branch (TRGB) of low-mass stars is found to be at I_TRGB_ = 21.55 +/- 0.1 mag and (V - I)_TRGB_ = 1.7+/-0.2 mag. The mean metallicity of the red giant branch (RGB) stars has been measured using the color of the RGB stars at M_I_ = -3.5 mag, (V - I)_-3.5_ = 1.41 +/- 0.07 mag: [Fe/H] = -1.6+/-0.2 dex. The distance modulus to NGC 3109 has been estimated using the I magnitude of the TRGB to be (m - M)_0_ = 25.45 +/- 0.15 mag for an adopted foreground extinction of A_I_ = 0.08 mag, showing a very good agreement with the Cepheid distance modulus estimate based on very recent CCD photometry, (m - M)_0_ = 25.5 +/- 0.2 mag (Capaccioli, Piotto, & Bresolin). |
