Masses of RRd variables using Livermore opal capacities

Abstract

The new Livermore opacities are used to construct 27 new stellar envelope models in order to determine if the discrepancy between the masses of the double-mode RR Lyrae variables using pulsation and evolution theories can be reconciled. For these extreme Population II variables, the large opacity increases found from the extensive line absorptions of iron around 250,000 K seen in Population I compositions are not realized. It is discovered that the opacity decreases below a temperature of 10{sup 5} K, due to more narrow lines of hydrogen than those used in the Los Alamos opacities, can also decrease theoretical period ratios. This opacity decrease, as with the higher temperature increases, produces steeper temperature increases and more shallow density gradients in the regions where the pulsation eigenvectors can feel the stellar structure. Small opacity increases at about 250,000 K can increase the more-metal-content RRd variables in the Oosterhoff I clusters by 0.1 solar mass. This essentially eliminates the inconsistency between masses from the two globular cluster types and between those determined from pulsation and evolution theories. 28 refs.