Carbon isotopic abundance ratios in S-type stars

Magnesium isotopic abundance ratios in cool stars

From high resolution spectra of 61 cool dwarfs and giants, Mg isotopic abundance ratios Mg:Mg:Mg are derived from spectral synthesis of the MgH A-X lines near 5140Å. Our sample spans the range −2.5 ≤ [Fe/H] ≤ 0.1, including the first measurements of Mg isotope ratios in stars with metallicities below [Fe/H]=−2.0. We confirm the decrease in Mg/Mg with decreasing [Fe/H] as predicted by recent mod...

Quantitative analysis of carbon isotopic ratios in carbon stars

We present the result of a quantitative analysis of 12C/13C ratios in 26 J-type carbon stars. The 12C/13C ratios are determined from lines of the CN red system around 8000 Å, using the iso-intensity method and line-blanketed model atmospheres. The average of 12C/13C ratios in the 26 stars is 4.7 ± 2.8 (standard deviation). All the stars studied, except for two stars, have 12C/13C ratios smaller...

Abundance Ratios in the Oldest Stars

Quantitative analysis of carbon isotopic ratios in carbon stars II. The effect of model atmosphere on the iso-intensity method

We discuss the analysis of 12C/13C ratios in cool carbon stars presented by de Laverny & Gustafsson (1998), who questioned the reliability of the iso-intensity method used by Ohnaka & Tsuji (1996). We show that the systematic discrepancy of 12C/13C ratios between Lambert et al. (1986) and Ohnaka & Tsuji (1996) cannot be attributed to the uncertainty of the iso-intensity method. The analysis of ...

Abundance Ratios in Early-Type Galaxies

Although evidence is accumulating that abundance ratios in galaxies are often non-solar, they are far from understood. I resume the current evidence for non-solar abundance ratios, supplementing the recent review by Worthey (1998) with some new results. It appears that the Mg/Fe abundance ratio only depends on the mass of the galaxy, not on the formation time-scale. For massive galaxies [Mg/Fe]...