A New Survey for Carbon-Enhanced Metal-Poor Stars in the Halo(es) of the Galaxy

Carbon-enhanced metal-poor (CEMP) stars are of astrophysical interest for a host of reasons, including their use as probes of the nucleosynthesis history of stellar populations in the Milky Way and other Local Group galaxies, and likely association with the same progenitors as the recently discovered carbon-rich damped Lyman-alpha clouds -- that is, the very first generations of stars. In the past, CEMP stars were discovered by targeting low-metallicity stellar candidates, based on their weak CaII K lines in objective-prism surveys, and hence passed over many CEMP stars with [Fe/H] > -2.5, or by targeting stars that exhibit strong carbon signatures based on the sum of carbon-line strengths in their spectra, biasing the selection towards cool stars. As a result, these schemes have likely MISSED large numbers of CEMP stars, particularly at intermediate metallicity (-2.5 < [Fe/H] < -1.0), a region sampling the inner-halo and metal-weak thick-disk populations of the Galaxy. A list of previously unidentified candidate CEMP stars from the Hamburg/ESO prism survey has been compiled, based on the strength of a newly developed CH G-band index. Follow-up medium-resolution spectroscopy for a sample of 441 candidates has thus far been obtained with GEMINI, SOAR, and the ESO/NTT (through semester 2012A). Of these, 130 stars possess [Fe/H] < -2 (74 with [C/Fe] > +0.5), 28 with [Fe/H] < -3.0 (17 with [C/Fe] > +0.5), and 3 with [Fe/H] < -4.0 (2 with [C/Fe] > +0.5). This has been one of the most successful searches dedicated to CEMP stars, and the outcome of this survey is of a great value for further analysis of the observed targets. High-resolution spectroscopy with the VLT, Magellan, and the AAT is already underway, and will provide full abundance analyses for the most interesting targets, enabling the classification of the sample into the CEMP-s and CEMP-no categories.