The cosmic origin of carbon and manganese

Abstract

We have determined carbon abundances for 51 dwarf stars and manganese abundances for 95 dwarf stars in two distinct and well defined stellar populations the Galactic thin and thick disks. As these two populations have different chemical histories we have been able to, through a differential abundance analysis using high-resolution spectra, constrain the formation sites for carbon and manganese in the Galactic disk(s). The analysis of carbon is based on the forbidden [C I] line at 872.7 nm which is an abundance indicator that is insensitive to errors in the stellar atmosphere parameters. Combining these data with our previously published oxygen abundances, based on the forbidden [O I] line at 630.0 nm, we can form very robust [C/O] ratios that we then used to investigate the origin of carbon and the chemical evolution of the Galactic thin and thick disks. We find that the [C/Fe] versus [Fe/H] abundance trends for the thin and thick disks are totally merged and being flat for sub-solar metallicities. The thin disk that extends to higher metallicities then shows a shallow decline in [C/Fe] from [Fe/H] ≈ 0 and up to [Fe/H] ≈ +0.4. The [C/O] versus [O/H] trends are well separated between the two disks (due to differences in the oxygen abundances) and bear great resemblance with the [Fe/O] versus [O/H] trends. Our interpretation of our abundance trends is that the sources that are responsible for the carbon enrichment in the Galactic thin and thick disks have operated on a time-scale very similar to those that are responsible for the Fe and Y enrichment (i.e., SN Ia and AGB stars, respectively). For manganese, when comparing our Mn abundances with O abundances for the same stars we find that the abundance trends in the stars with kinematics typical of the thick disk can be explained by metallicity dependent yields from SN II. Furthermore, the [Mn/O] versus [O/H] trend in the halo is flat. We conclude that the simplest interpretation of our data is that manganese most likely is produced in SN II and that the Mn yields for such SNae must be metallicity dependent.