A New CEMP-s RR Lyrae Star

TL;DR

This paper identifies SDSS J1707+58 as a rare, extremely metal-poor RR Lyrae star with significant carbon and barium enhancements, expanding the known class of CEMP-s RR Lyrae stars and providing new insights into their properties.

Contribution

It reclassifies SDSS J1707+58 as a CEMP-s RR Lyrae star and reports the discovery of other potential CEMP candidates among RR Lyrae stars.

Findings

SDSS J1707+58 is one of the most metal-poor RR Lyrae stars known.

It has extreme [C/Fe] and [Ba/Fe] enhancements.

Twelve other RR Lyrae stars with high [C/Fe] are identified as candidates.

Abstract

We show that SDSS J170733.93+585059.7 (hereafter SDSS J1707+58), previously identified by Aoki and collaborators as a carbon-enhanced metal-poor star (with s-process-element enhancements; CEMP-s), on the assumption that it is a main-sequence turn-off star, is the RR Lyrae star VIII-14 identified by the Lick Astrograph Survey. Revised abundances for SDSS J1707+58 are [Fe/H] = -2.92, [C/Fe] = +2.79, and [Ba/Fe] = +2.83. It is thus one of the most metal-poor RR Lyrae stars known, and has more extreme [C/Fe] and [Ba/Fe] than the only other RR Lyrae star known to have a CEMP-s spectrum (TY Gru). Both stars are Oosterhoff II stars with prograde kinematics, in contrast to stars with [C/Fe] < +0.7, such as KP Cyg and UY CrB, which are disk stars. Twelve other RR Lyrae stars with [C/Fe] >= +0.7 are presented as CEMP candidates for further study.