170 research outputs found
The Stellar Populations of the Carina Dwarf Spheroidal Galaxy: I. a New Color-Magnitude Diagram for the Giant and Horizontal Branches
We report on the first in a series of studies of the Carina dwarf spheroidal
galaxy, a nearby satellite of our Galaxy. Our two major results are: 1) precise
BI photometry (\sigma_{B-I} \simlt 0.05 for V \simlt 22) for 11,489 stars
in the Carina field, and 2) the detection of two, morphologically distinct,
horizontal branches, which confirms that star formation in Carina occurred in
two well-separated episodes. The old horizontal branch and RR Lyrae instability
strip belong to a > 10 Gyr stellar population, while the populous red-clump
horizontal branch belongs to an approximately 6 Gyr stellar population. We
derive a distance modulus for Carina from the apparent
magnitudes of the old horizontal branch and the tip of the red giant branch,
and discuss modifications to the previously estimated distance, total
magnitude, and stellar ages. Using the color of the red giant branch, we
estimate the metallicities of the younger and older populations to be [Fe/H] =
-2.0 and -2.2, respectively.Comment: 18 pages, 9 figures, uses AAS LaTex macros, PostScript figures
available through anonymous ftp, accepted for publication in the Astronomical
Journal, DAO-tsh94-
Constraints on the Origin of Manganese from the Composition of the Sagittarius Dwarf Spheroidal Galaxy and the Galactic Bulge
The trend of [Mn/Fe] in the Galactic bulge follows the solar-neighborhood
relation, but most stars in the Sagittarius dwarf spheroidal galaxy show
[Mn/Fe] deficient by approximately 0.2 dex. This leads us to conclude that the
Mn yields from both type Ia and type II SNe are metallicity-dependent. Our
observations militate against the idea, suggested by Gratton, that Mn is
over-produced by type Ia SNe, relative to type II SNe. We predict Mn/Fe ratios,
lower than the solar neighborhood relation, for the younger populations of
nearly all dwarf galaxies, and that Mn/Fe ratios may be useful for tracing the
accretion of low-mass satellites into the Milky Way.Comment: 10 pages, 3 figures, accepted for publication in ApJ
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