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Session 38 - Dwarf Galaxies.
Display session, Tuesday, January 14
Metropolitan Ballroom,

[38.04] HST WFPC2 Observations of Two Dwarf Spheroidal Galaxies in the M81 Group

T. E. Armandroff (KPNO/NOAO), N. Caldwell (FLWO), G. S. Da Costa (MSSSO), P. Seitzer (U. Mich.)

The M81 group is one of the nearest groups of galaxies to our own, but its properties are quite different from those of the Local Group. It has therefore provided a different evolutionary environment for its member galaxies. This team has carried out a CCD survey of the M81 group to search for analogs to the Local Group dwarf spheroidal (dSph) galaxies. We have recovered all of the M81 dwarf candidates previously identified in photographic surveys and, in addition, have discovered several new systems whose surface brightnesses place them within the range of values found for the Local Group dSphs. We have obtained WFPC2 images with the F555W and F814W filters for two M81 dSph candidates: F8D1 and BK5N. We have performed photometry on these images and constructed color--magnitude diagrams that show the upper two magnitudes of the giant branch. Based on the resulting I magnitude of the giant branch tip, the distances for both galaxies are consistent with membership in the M81 group. Although similar in central surface brightness, F8D1 is 3.5 magnitudes more luminous than BK5N. Thus, F8D1 is likely related to the large low-surface-brightness galaxies found in the Virgo cluster by Impey et al.\ (1988, ApJ, 330, 634). The mean color of the giant branch is used to establish the mean abundance of each galaxy through comparison with the giant branches of standard globular clusters. F8D1, the more luminous galaxy, is significantly more metal rich than BK5N. A full discussion of our results will be given in the poster.

Program listing for Tuesday