The chemical inhomogeneity of the Draco dwarf spheroidal galaxy
Spectra of 7-A resolution have been obtained of six red giants in the Draco dwarf spheroidal galaxy by using the Multiple Mirror Telescope. Indices sensitive to the strength of the lambda3883 CN band, the Ca II H and K lines, and the lambda4300 G band have been measured. Stars in the globular clusters M13 and M92 were observed for comparison. The new spectra confirm that a range in calcium abundance exists among the Draco giants, a result found previously by Zinn and by Kinman, Kraft, and Suntzeff. The calcium variations are also accompanied by correlated variations of the CN and G bands. Most Draco stars appear to be intermediate between M92 and M13 in their heavy-element abundances. However, the present spectrum of star 119 confirms Kinman, Kraft, and Suntzeff's discovery of a calcium abundance that is considerably lower than that of M92. The MMT spectra also indicate that one star, 361, has a (C/Fe) ratio higher than is typical of globular clusters. A reanalysis of DDO photometry published by Hartwick and McClure indicates that (C/Fe) enhancements are present among other Draco giants. A possible origin for the Draco anomalies is discussed, and similarities to the globular cluster ..omega.. Cen are pointed out. It is suggested that Draco formed from a relatively massive (approx.10/sup 6/ M/sub sun/) gas cloud in which the star formation was very inefficient. Supernova activity not only produced chemical inhomogeneities among the Draco stars, but also caused the removal of approx.90% of this system's original gas. Globular clusters, on the other hand, are postulated to be much more efficient at forming stars and have lost a smaller percentage of their initial mass.
- Research Organization:
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138
- OSTI ID:
- 6747063
- Journal Information:
- Astron. J.; (United States), Vol. 89:6
- Country of Publication:
- United States
- Language:
- English
Similar Records
Dwarf spheroidal galaxy in Draco. IV. On the mean metal abundance and metal-abundance range of the red giant stars
Metal abundance range in the Draco dwarf galaxy
Related Subjects
GENERAL PHYSICS
GALAXIES
CHEMICAL COMPOSITION
RED GIANT STARS
VISIBLE SPECTRA
ABUNDANCE
CALCIUM
GALACTIC EVOLUTION
ORIGIN
PHOTOMETRY
STAR CLUSTERS
ALKALINE EARTH METALS
ELEMENTS
GIANT STARS
METALS
SPECTRA
STARS
640105* - Astrophysics & Cosmology- Galaxies
640102 - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources