This dissertation focuses on abundance analyses of carbon-enhanced metal-poor (CEMP)Galactic halo stars. Different methods for determining carbon, nitrogen, oxygen, andalso some barium abundances are described. The study of these abundances in suchstars serves to investigate the means by which the Universe became enriched in metals.Due to the different kinds of CEMP stars observed in the Milky Way, it can onlybe assumed that there is certainly more than one method of carbon-enhancement atearly times. Complete abundance analyses for as many of these archaeological relicsas possible are needed in order to constrain the astrophysical sites of early carbonproduction.There are three main parts of this dissertation. The first part describes new techniquesto determine oxygen abundances from spectra of the near-infrared molecularCO bands. With the near-IR OSIRIS spectrograph on the SOAR 4.1-m telescope, 57CEMP stars were observed. A wide range of oxygen abundances were estimated, andthe results were statistically compared to high-resolution estimates for both carbonenhancedand carbon-normal metal-poor stars. Abundance patterns of the samplestars were compared to yield predictions for very metal-poor asymptotic giant branch(AGB) stars. The majority of the sample exhibit patterns consistent with CEMPstars having s-process-element enhancements, and thus have very likely been pollutedby carbon- and oxygen-enhanced material transferred from a metal-poor AGBcompanion.The second part delineates a new survey effort implemented in order to identifynew CEMP stars. For the initial pilot study, a new selection technique was developedbased solely on the strength of the CH G band at 4300 °A. This technique eliminatedprevious temperature and metallicity biases present in other CEMP surveys. Observationsof the pilot sample were carried out with the Goodman HTS spectrographon the SOAR 4.1-m telescope. Of the over 120 candidate stars observed, over 35%were found to be CEMP stars. The selection technique was then improved to includea second index for the strength of the G band, and the survey was continued onboth the SOAR and Gemini telescopes. After this extension, the success rate of thisprogram increased to 50%.The final part of this dissertation contains details of a pilot study of known metalpoorstars using the X-Shooter spectrograph on the Very Large Telescope (VLT).With three spectrograph arms (near-ultraviolet, optical, and near-infrared), this instrumentwas used to calculate carbon, nitrogen, oxygen, and barium abundances fora sample of 27 CEMP stars. The broad spectral range of this instrument is unprecedented,and it is an efficient way to estimate abundances for several pertinent speciesin just one exposure per star. Of the 27 stars, many proved to be enhanced in carbon.The majority appear to be consistent with s-process-element enhancement, but therewas one extremely metal-poor star which falls into the rare family of CEMP starswith no neutron-capture-element enhancement.
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