Extremely metal-poor stars. IX. CS 22949-037 and the role of hypernovae

Abstract

We have obtained high-resolution spectra of the extremely metal-poor star CS 22949-037 ([Fe/H] = -3.79) in the region of the ultraviolet NH bands at 3360-3370 Å, which confirm our earlier report that it exhibits extreme nitrogen enhancement. We find [N/Fe] = 2.3 ± 0.4. The star is also known to have large relative overabundances, of order 0.5-1 dex, of carbon and the α-elements. This abundance pattern is not explained by any standard Galactic chemical enrichment model of which we are aware. The large N enhancement is, however, predicted by the zero heavy element, M ≳ 200 M⊙, hypernova models of Woosley & Weaver and Fryer, Woosley, & Heger. If the rotating models of Fryer et al. are relevant to the enrichment of CS 22949-037, one might expect it to possess a large overabundance of oxygen, with a mass fraction similar to or larger than that of nitrogen, and an [O I] λ6300.3 line strength of ∼ 2-8 mÅ. Show more