The Nature of Metal-Poor Carbon-Enhanced Stars in the Galaxy

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"The Nature of Metal-Poor Carbon-Enhanced Stars in the Galaxy"AST-0098549For the first time, there is now an adequate sample of stars to use as probes in decoding the initial phases of galactic evolution thanks to surveys that were carried out in the 1990s by the PI and colleagues for extremely metal poor stars. New surveys covering a volume in space 4 times as large are now underway with Hamburg/ESO objective prism material. Among the most metal poor stars, carbon enhancements become common and it is already clear that the mechanism responsible for this must be very different from that which provides carbon excesses in the atmospheres of more metal rich stars. The work carried out under this award will be a spectroscopic follow-up to the survey to identify the cause of the enhancement. Various suggestions have been made including contamination of the pre-stellar material by supernovae type II or by a type of nuclear burning which is not found in more metal-rich stars. Medium-resolution spectroscopy for a large sample of these stars is planned in order to identify trends. This will be complemented by high-resolution spectroscopy for a representative subsample to provide the constraints on plausible nucleosynthesis pathways and evolutionary scenarios.