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Element Abundances of Evolved Stars in the Galactic Globular Cluster M5

Ramesh Kumar, Karthigeyan

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

I present the iron abundance and abundance ratios for 9 elements: Si I, Ca I, Ti I and Ti II, Cr I, Y II, Ce II, Nd II and Er II with respect to Fe in a sample of 55 stars along the RGB and AGB of the globular cluster M5. The spectra were obtained using the Hectochelle spectrograph at the Multiple Mirror Telescope. The spectral coverage was from 5070 Å to 5390 Å, 6010 Å to 6510 Å and 6391 Å to 6873 Å. An average iron abundance [Fe/H]=−1.29±0.15 dex was found, consistent with Harris (2010). The cluster averages of [Si/Fe], [Ca/Fe], [Ti I/Fe], [Ti II/Fe], [Cr/Fe], [Ce/Fe], [Nd/Fe] and [Er/Fe] are 0.16 ± 0.17, 0.13 ± 0.12, 0.4 ± 0.15, 0.31 ± 0.13, 0.10 ± 0.41, 0.01 ± 0.16, 0.13 ± 0.13, 0.52 ± 0.14, 1.27 ± 0.18 dex, respectively. The [Ti II/Fe] matches the literature value. The [Si I/Fe] and [Ca/Fe] are found to be lower than the reported values while the other elements of this study show a higher abundance.An anti-correlation is found between the abundance ratios and the iron abundance which can be explained due to an artificially high spread in [Fe/H]. The combined behaviour of α-elements is also studied and we report an enhancement of α-elements relative to iron seen in this cluster. The abundance variations do not show any trend with the distance from the cluster centre. The obtained spectroscopic temperatures are found to match the photometric temperatures within the error margins except for three stars. An attempt is made to differentiate the RGB and AGB stars using their derived masses. The systematic offset in ∆Tef f between RGB and AGB prevents us from accurately calculating the mass loss in the RGB.