NUCLEOSYNTHESIS AND THE INHOMOGENEOUS CHEMICAL EVOLUTION OF THE CARINA DWARF GALAXY

Abstract

The detailed abundances of 23 elements in nine bright RGB stars in the Carina\ndSph are presented based on high resolution spectra gathered at the VLT and\nMagellan telescopes. A spherical model atmospheres analysis is applied using\nstandard methods to spectra ranging from 380 to 680 nm. The stars in this\nanalysis range from -2.9 < [Fe/H] < -1.3, and adopting the ages determined by\nLemasle et al. (2012), we are able to examine the chemical evolution of\nCarina's old and intermediate-aged populations. One of the main results from\nthis work is the evidence for inhomogeneous mixing in Carina; a large\ndispersion in [Mg/Fe] indicates poor mixing in the old population, an offset in\nthe [alpha/Fe] ratios between the old and intermediate-aged populations (when\nexamined with previously published results) suggests that the second star\nformation event occurred in alpha-enriched gas, and one star, Car-612, seems to\nhave formed in a pocket enhanced in SN Ia/II products. This latter star\nprovides the first direct link between the formation of stars with enhanced SN\nIa/II ratios in dwarf galaxies to those found in the outer Galactic halo (Ivans\net al. 2003). Another important result is the potential evidence for SN II\ndriven winds. We show that the very metal-poor stars in Carina have not been\nenhanced in AGB or SN Ia products, and therefore their very low ratios of\n[Sr/Ba] suggests the loss of contributions from the early SNe II. Low ratios of\n[Na/Fe], [Mn/Fe], and [Cr/Fe] in two of these stars support this scenario, with\nadditional evidence from the low [Zn/Fe] upper limit for one star. It is\ninteresting that the chemistry of the metal-poor stars in Carina is not similar\nto those in the Galaxy, most of the other dSphs, or the UFDs, and suggests that\nCarina may be at the critical mass where some chemical enrichment events are\nlost through SN II driven winds.\n