A NEW CEMP-s RR LYRAE STAR

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 metalpoor 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.

CEMP-s and CEMP-s/r stars: last update

“…It is noteworthy that SDSS J1707+58 is now discovered to be an RR Lyrae star (Kinman et al 2012;see Stancliffe et al 2013 for a theoretical interpretation), instead of a main-sequence CEMP-s star . SDSS J1707+58 is one of the most metal-poor RR Lyrae stars known to date with [Fe/H] = −2.92, about 0.4 dex lower than that found by Aoki et al (2008).…”

Improving the cosmic distance ladder. Distance and structure of the Large Magellanic Cloud

“…A few high resolution spectroscopic studies of elemental abundances of RR Lyrae stars are also found in the literature (Butler et al 1976(Butler et al , 1979Clementini et al 1995;Lambert et al 1996;Kolenberg et al 2010;For et al 2011;Kinman et al 2012;Govea et al 2014, Pancino et al 2014, submitted to MNRAS). For variables in globular clusters, individual metal abundances can be inferred from the accepted metallicities of the host clusters 2 .…”

Seven New Carbon-Enhanced Metal-Poor Rr Lyrae Stars

“…The RR Lyrae stars observed for this pilot program, listed in Kinman et al (2012), were selected from the Hamburg/ESO objective-prism survey, cross-matched with previously recognized RR Lyraes. The benefit of drawing CEMP candidates from the Hamburg/ESO Survey (HES) is that (rather crude) preliminary estimates of [Fe/H] and [C/Fe] from their low-resolution spectra are available (Christlieb et al 2008).…”

“…Like the RR Lyrae variables studied in globular clusters, RR Lyrae field stars have been shown to exhibit properties of both Oo I and Oo II systems (Kinemuchi et al 2006), although the separation between the two populations is far less distinct. Following Kinman et al (2012), we study the Oosterhoff types of the CEMP RR Lyrae field stars in order to compare to classical Oosterhoff systems, as well as to explore how the presence of carbon in the atmosphere might affect the nature of the pulsation.…”

“…Prior to our observational program, only two CEMP RR Lyrae stars had been recognized (Preston et al 2006;Kinman et al 2012). Now, the sample size has increased by more than a factor of four, as we have identified seven new CEMP RR Lyrae stars.…”