A New CEMP-s RR Lyrae Star
T. D. Kinman (1), W. Aoki (2), T. C. Beers (1), W.R. Brown (3) ((1), National Optical Astronomy Observatory, Tucson, AZ, USA, (2) National, Astronomical Observatory of Japan, Tokyo, Japan, (3) Smithsonian, Astrophysical Observatory, Cambridge, MA, USA)

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.
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