Near-infrared spectroscopy of carbon-enhanced metal-poor stars. I. A SOAR/OSIRIS pilot study

We report on an abundance analysis for a pilot study of seven carbon-enhanced metal-poor (CEMP) stars, based on medium-resolution optical and near-infrared spectroscopy. The optical spectra are used to estimate [Fe/H], [C/Fe], [N/Fe], and [Ba/Fe] for our program stars. The near-infrared spectra, obtained during a limited early science run with the new SOAR 4.1 m telescope and the Ohio State Infrared Imager and Spectrograph, are used to obtain estimates of [O/Fe] and C-12/C-13. The chemical abundances of CEMP stars are of importance for understanding the origin of CNO in the early Galaxy, as well as for placing constraints on the operation of the astrophysical s-process in very low metallicity asymptotic giant branch stars. This pilot study includes a few stars with previously measured [Fe/H], [C/Fe], [N/Fe], [O/Fe], C-12/C-13, and [Ba/Fe], based on high-resolution optical spectra obtained with large-aperture telescopes. Our analysis demonstrates that we are able to achieve reasonably accurate determinations of these quantities for CEMP stars from moderate-resolution optical and near-infrared spectra. This opens the pathway for the study of significantly larger samples of CEMP stars in the near future. Furthermore, the ability to measure [Ba/Fe] for (at least the cooler) CEMP stars should enable one to separate stars that are likely to be associated with s-process enhancements (the CEMP-s stars) from those that do not exhibit neutron-capture enhancements (the CEMP-no stars).