AAS Meeting #193 - Austin, Texas, January 1999
Session 8. Galactic Morphology and Stellar Populations
Display, Wednesday, January 6, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[8.05] HST/WFPC2 Observations of the Andromeda II Dwarf Spheroidal Galaxy

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

Images have been obtained with the Hubble Space Telescope WFPC2 camera of the central regions of Andromeda II, a dwarf spheroidal (dSph) galaxy that lies in the outer halo of M31. The resulting color--magnitude diagrams reveal for the first time the morphology of the horizontal branch in this system. We find that, in a similar fashion to many of the Galactic dSph systems, the horizontal branch of And II is predominantly red, though blue horizontal branch stars and RR Lyrae variable stars are also found. A comparison with the giant branches of standard Galactic globular clusters indicates a mean abundance for And II that is somewhat more metal rich than And I (for which <[Fe/H]> = --1.45 dex). The color width of the And II red giant branch is significantly larger than the photometric errors, indicating a range of metal abundance in And II. We will comment further on the metal abundance distribution at the meeting. Given the abundance distribution and the horizontal branch morphology, And II exhibits the second parameter effect, although in a more modest manner than And I (which has a somewhat redder horizontal branch and is somewhat more metal poor). The distance to And II has been determined based on the magnitude of the blue horizontal branch stars. We find that And II has a somewhat smaller distance modulus than M31 and And I by a few tenths of a magnitude. Full results will be presented at the meeting.

The author(s) of this abstract have provided an email address for comments about the abstract: armand@noao.edu

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