A Search for Metal-Poor Stars in the Halo of the Milky Way

Mohammed, Aruba and Sobral, David and Simmons, Brooke (2023) A Search for Metal-Poor Stars in the Halo of the Milky Way. Masters thesis, Lancaster University.

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Abstract

Metal-poor stars are essential in developing an understanding of the nature of the early Universe and the first stars. This study is based on the investigation by Jenkins et al. (2019), which used the data that Sobral et al. (2017) gathered from the COSMOS field using the Isaac Newton Telescope (INT) between 2013 and 2015, for the CALYMHA survey. The catalogue contained 123,505 sources and the aim of the investigation was to discover Pop III stars or their direct descendants. The goal of this research was the same; to discover potential metal-poor candidate stars in the halo of the Milky Way, with an emphasis on extremely metal-poor (EMP: [Fe/H] Using the same catalogue of sources as Jenkins et al. (2019), I was able to initially adopt and improve their approach to identify 165 metal-poor candidates. I used 102 theoretical spectra from the Pollux database with complete integer metallicities ([Fe/H]) of 0 to -5 to compute magnitude values for multiple filters: NB392, g, u and i, which were then used to estimate metallicities of the 165 candidate metal-poor stars via colour-colour plots and metallicity heatmaps. 16 EMP and 38 UMP candidate stars were identified. The correlation between temperature and g-i values was also explored and used to classify the 165 candidates. The distance of the stars with a [Fe/H] < -3 was estimated based on approximations and I found that 41 UMP and EMP candidates sit within 66kpc, and therefore can be reasonably approximated to sit within the Milky Way Halo. Number densities for the candidate F,G and K-type stars identified in this study are (1.50±0.81)×10−13 pc−3, (7.64±1.89) ×10−12 pc−3 and (1.91±0.34) × 10−9 pc−3 respectively, which follows the pattern reported in literature. Finally, I created a metallicity distribution function (MDF) for the candidate stars which follows the predicted MDF and F-type stars are shown to peak around [Fe/H] = -1.5 which is close to the literature value of [Fe/H] = -1.6.