SPECTROSCOPY OF GIANT STARS IN THE DRACO AND URSA MINOR DWARF GALAXIES

• Published in: Publications of the Astronomical Society of the Pacific Vol. 96; no. 576; pp. 128 - 142
• Main Author: STETSON, PETER B.
• Format: Journal Article
• Language: English
• Published: Chicago, IL The Astronomical Society of the Pacific 01.02.1984; University of Chicago Press
• Subjects: Astronomy; Carbon stars; Dwarf spheroidal galaxies; Dwarf stars; Earth, ocean, space; Exact sciences and technology; Giant and subgiant stars; Giant stars; Globular star clusters; Horizontal branch stars; Metal abundance; Normal stars (by class): general or individual; Radial velocity; Stars; Stellar spectra; Globular cluster; Radial velocity; Giant; Dwarf galaxies; Spectroscopical observation
• ISSN: 0004-6280; 1538-3873
• DOI: 10.1086/131311

Spectroscopic observations are presented for giant stars in the Draco and Ursa Minor dwarf spheroidal galaxies and in the galactic globular clusters M3, M92, M15, and M2. In Draco, strong star-to-star variations in the strengths of the H and lines of ionized calcium are found; when compared to line strengths of stars in the fiducial globular clusters the data suggest that [Fe/H] ranges from — 1.8 to — 2.9 in Draco, in agreement with other published data. Similar, though less numerous observations of Ursa Minor stars suggest a smaller range of metallicity— from — 1.8 to — 2.2 in [Fe/H], which may merely reflect the observational scatter. The strengths of the G bands of CH in the Draco and Ursa Minor spectra also show star-to-star scatter. On the average, the G bands in the dwarf spheroidal giants seem anomalously strong compared to globular cluster giants of similar metallicity, although some individual stars have globular cluster-like G: H + ratios. Radial velocities derived from these spectra are subject to systematic errors that are not wholly understood, but they are adequate to suggest the following: (1) one candidate UV-bright star in the Draco field is a nonmember while all other Draco stars observed, including a UV-bright star, a carbon star, and a blue suprahorizontal-branch star in addition to the normal red giants, are probable members; (2) all Ursa Minor stars observed are probable members; (3) the systemic radial velocities of Draco and Ursa Minor are close to -296 ± 5 km s" 1 and -255 ± 7 km s" 1 , respectively; and (4) an internal velocity dispersion as large as 10 km s" 1 in Draco is unlikely at about the 95% confidence level, although a smaller dispersion cannot be ruled out with confidence.