Color‐Magnitude Diagrams of Resolved Stars in Virgo Cluster Dwarf Galaxies

The Advanced Camera for Surveys (ACS) on HST has been used to image twofields in the core of the Virgo cluster that contain a number of dwarfelliptical galaxies. The combined F555W and F814W images have resolved redgiant stars in these galaxies, down to 1 mag below the giant branch tip. Two ofthe galaxies were targeted because of their extremely low central surfacebrightnesses (Bo > 27.0), thus the successful resolution into stars confirmsthe existence of such tenuous galaxies. Red giant stars were also found thatare not ostensibly associated with any galaxy. Color-magnitude diagrams in Vand I have been derived and used to derive distances and metallicities via themagnitude and mean color of the red giant branch tip. The mean abundances ofstars in the dwarfs range from -1.2 [Fe/H] < -2.4, and fall along the relationbetween galaxy luminosity and metallicity found for Local Group and M81 groupdwarf ellipticals. The mean distance modulus of the six Virgo galaxies is 31.0+/- 0.05, or 16.1 +/- 0.4 Mpc, whereas that for the intracluster stars in thosefields is 31.2 +/- 0.09 (17.4 +/- 0.7 Mpc).