A detailed study of giants and horizontal branch stars in M68 : atmospheric parameters and chemical abundances




Schaeuble, Marc-Andre

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In this thesis, I present a detailed high-resolution spectroscopic study of post main sequence stars in the Globular Cluster M68. My sample, which covers a range of 4000 K in Teff, and 3.5 dex in log(g), is comprised of members from the red giant, red horizontal, and blue horizontal branch, making this the first high-resolution globular cluster study covering such a large evolutionary and parameter space. Initially, atmospheric parameters were determined using photometric as well as spectroscopic methods, both of which resulted in unphysical and unexpected Teff, log(g), vt, and [Fe/H] combinations. I therefore developed a hybrid approach that addresses most of these problems, and yields atmospheric parameters that agree well with other measurements in the literature. Furthermore, my derived stellar metallicities are consistent across all evolutionary stages, with <[Fe/H]> = 2.42 ( sigma = 0.14) from 25 stars. Chemical abundances obtained using my methodology also agree with previous studies and bear all the hallmarks of globular clusters, such as a Na-O anti-correlation, constant Ca abundances, and mild r-process enrichment.



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