Stellar Populations of the Dwarf Galaxy UKS 2323−326 in the Sculptor Group

We present deep BVRI CCD photometry of the stars in the dwarf irregulargalaxy UKS 2323-326 in the Sculptor Group. The color-magnitude diagrams of themeasured stars in UKS 2323-326 show a blue plume which consists mostly of youngstellar populations, and a well-defined red giant branch (RGB). The tip of theRGB is found to be at I_TRGB = 22.65 +/- 0.10 mag. From this the distance tothis galaxy is estimated to be d = 2.08 +/- 0.12 Mpc. The correspondingdistance of this galaxy from the center of the Local Group is 1.92 Mpc, showingthat it is located outside the Local Group. The large distance, combined withits velocity information, indicates that it is very likely to be a member ofthe Sculptor Group. The mean metallicity of the red giant branch is estimatedto be [Fe/H] = -1.98 +/- 0.17 dex. Total magnitudes of UKS 2323-326 (< r_H = 70arcsec) are derived to be B^T=14.07 mag, V^T=13.50 mag, R^T=13.18 mag, andI^T=12.83 mag, and the corresponding absolute magnitudes are M_B=-12.58 mag,M_V=-13.14 mag, M_R=-13.45 mag, and M_I=-13.79 mag. Surface brightness profilesof the central part of UKS 2323-326 are approximately consistent with a Kingmodel with a core concentration parameter c = log (r_t / r_c) ~= 1.0, and thoseof the outer part follow an exponential law with a scale length of 21 arcsec.The magnitudes and colors of the brightest blue and red stars in UKS 2323-326(BSG and RSG) are measured to be, respectively, _{BSG} = 20.33 +/- 0.25mag, <(B-V)(3)>_{BSG} = 0.14 +/- 0.07 mag, _{RSG} = 20.74 +/- 0.18 mag,and <(B-V)(3)>_{RSG} = 1.35 +/- 0.08 mag. The corresponding absolute magnitudesare derived to be _{BSG} = -6.31 mag and _{RSG} = -5.91 mag,which are about half magnitude fainter than those expected from conventionalcorrelations with galaxy luminosity.Comment: Latex file, 16 pages with 9 figures, uses emulateapj.sty To appear in the AJ (in August 1999