Back to Volume
Paper: The Composition of the Sagittarius Dwarf Spheroidal Galaxy, and Implications for Nucleosynthesis and Chemical Evolution
Volume: 336, COSMIC ABUNDANCES as Records of Stellar Evolution and Nucleosynthesis in honor of David L. Lambert
Page: 221
Authors: McWilliam, A.; Smecker-Hane, T.A.
Abstract: We outline the results of a study of the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). For the Sgr dSph stars with [Fe/H] ≥ −1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the α-elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old metal-poor population, including products of AGB stars and type Ia supernovae (SN).

We suggest two scenarios to explain the observations: First, is chemical enrichment over long time-scales in a galaxy which has experienced significant mass-loss during its evolution. The second possibility is that we are seeing the products of chemical enrichment from a system which experienced a large burst of star-formation, followed by a quiescent period of many Gyr. Both of these scenarios can lead to the situation where newly synthesized material from AGB stars and type Ia SN overwhelms nucleosynthesis products from a minor population of young, metal-rich, stars. It is likely that both mechanisms operate in the Sgr dSph.

Since these conditions should be generally applicable to low-mass systems, we expect to find similar abundance patterns in other dwarf galaxies. This is supported by the chemical composition of stars in the Galactic globular cluster ω Cen and in the Fornax dwarf galaxy, suggesting that both shared a history similar to the Sagittarius dwarf spheroidal galaxy.

Back to Volume