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The Chemistry and Properties of Stars in NGC 362

Ben Assayag, Lucas

[Thesis]. Manchester, UK: The University of Manchester; 2014.

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Abstract

Abundance studies in Galactic globular clusters increase knowledge of the chemical enrichment of the Universe and the formation of stars or galaxies.This thesis presents chemical abundances for iron, calcium, silicon and titanium in 56 stars in the Galactic globular cluster NGC 362 from spectra obtained with FLAMES, the multi-object spectrograph at the Very Large Telescope. The abundances were derived using equivalent width measurements. This study covered wavelengths from 6300 to 6900 A.The average iron abundance derived is [Fe/H] = –1.26 +/- 0.03 dex, consistent with previous studies. An unexpected scatter was found, explained by the presence of blended stars and the decision to determine each atmospheric parameter (T_eﬀ ,log(g), v_t and [Fe/H]) independently of photometric measurements. It might be better to ﬁx one of them for future studies.The average sodium, silicon and calcium abundances are also in agreement with the literature. We determined [Na/Fe] = 0.11 +/- 0.18 dex, [Si/Fe] = 0.25 +/- 0.13dex and [Ca/Fe] = 0.38 +/- 0.06 dex. The titanium abundance determined in this thesis is higher by ∼ 0.40 dex than previous studies, due to eﬀects caused by theproximity of the 6562 A Hα line. The measured abundance for this study is [Ti/Fe] = 0.56 +/- 0.20 dex.The enhancement of the α elements (Si, Ca and Ti) suggests an enrichment fromType II Supernovae (SNe) and minimal contributions from Type Ia SNe.