AN ABUNDANCE ANALYSIS OF THE BRIGHT RV TAURI VARIABLE R SCUTI.

Abstract

ABSTRACT A fine-analysis of the bright RV Tauri-type variable R Scuti is given. The analysis derives from a single high-dispersion echellogram obtained near secondary light minimum. The derived atmospheric parameters at that time were as follows: effective temperature, 4400 K; log g, 0.0; and Fe/H abundance ratio, -0.9. The light metals are present with solar ratios, but the s-process elements are underabundant by factors close to 10. This abundance pattern is strikingly different from that seen in normal halo and old-disk dwarfs and red giants, which exhibit nonsolar s-process abundance ratios only when the Fe/H ratio is less than -2. Several W Virginis variables with only modest iron deficiencies, however, are known to show similar s-process underabundances. The results may indicate that s-process production in the early stages of disk formation was spatially inhomogeneous. If such s-process deficiencies are confined to the RV Tauri and W Virginis variables, however, an alternative hypothesis is that these are highly evolved, hydrogen-deficient halo stars that originally had very low iron contents.