STELLAR POPULATIONS IN THE DWARF ELLIPTIC GALAXY NGC-147

Deep V and I CCD images in a central and an outer field of the Local G roup dwarf elliptical galaxy NGC 147 have been obtained with the Wide Field and Planetary Camera-2 (WFPC2) on board of the Hubble Space Tele scope. The color-magnitude diagram shows a number of interesting featu res, including a well defined red giant branch (RGB); a red horizontal branch (HB), a strong red clump, and a small number of extended asymp totic giant branch (EAGB) stars. A mean distance modulus of (m-M)(0)=2 4.39 is derived based on both the HB and the RGB tip brightness. The m etallicity [Fe/H] as determined from the RGB color has a mean value of -0.91 in the central field, and -1.0 in the outer field; and the oute r field shows a weak tendency of increasing metallicity with galactoce ntric radius. A metallicity dispersion is also present in the galaxy, and it shows a clear radial variation in the sense that a larger dispe rsion is seen at smaller radii. The small population of EAGB stars ind icates the presence of intermediate-aged (several Gyr) stars in the ga laxy, while the absence of the main sequence stars with M(V)<1 shows t hat star formation ceased at least 1 Gyr ago. The distribution of the EAGB stars indicates that the younger stars are more centrally concent rated than the majority of older stars. A similar age gradient is also implied by the relative distribution of the HB stars, which appear to be more populous at larger radii. These results are considered within the context of theoretical models for the evolution of dwarf elliptic al galaxies. (C) 1997 American Astronomical Society.