An Internal Second-Parameter Problem in the Sculptor Dwarf Spheroidal Galaxy
Abstract
We present BV photometry of the Sculptor dwarf galaxy to V=22. These data give evidence for a bimodality in Sculptor's metallicity distribution based on a discontinuity in the luminosities of horizontal-branch (HB) stars and by the presence of two distinct red giant branch (RGB) bumps. A consistent picture of the evolved stars in Sculptor is given by the presence of (1) a metal-poor population of [Fe/H]~-2.3 with an exclusively blue HB and that corresponds to the blueward side of the Sculptor RGB and the more luminous RGB bump, and (2) a less metal-poor population of [Fe/H]~-1.5 required to explain the less luminous red HB, the red side of the RGB, and a second, less luminous RGB bump. Best fits to the HB populations are obtained with enhanced oxygen abundances, [O/Fe]~+0.5. Variations in the global HB and RGB morphology of Sculptor can be explained by differences in the radial distribution of the two different [Fe/H] populations. The presence of these two populations shows that the Sculptor dwarf galaxy has an internal second-parameter problem.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1999
- DOI:
- 10.1086/312133
- arXiv:
- arXiv:astro-ph/9905238
- Bibcode:
- 1999ApJ...520L..33M
- Keywords:
-
- GALAXIES: ABUNDANCES;
- GALAXIES: DWARF;
- GALAXIES: INDIVIDUAL: NAME: SCULPTOR;
- GALAXIES: STELLAR CONTENT;
- GALAXIES: LOCAL GROUP;
- STARS: HORIZONTAL-BRANCH;
- Galaxies: Abundances;
- Galaxies: Dwarf;
- Galaxies: Individual: Name: Sculptor;
- Galaxies: Stellar Content;
- Galaxies: Local Group;
- Stars: Horizontal-Branch;
- Astrophysics
- E-Print:
- 15 pages, 4 figures, LaTeX, uses aastex. Accepted by ApJ Letters