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

Research output: ThesisMaster's Thesis

  • Aruba Mohammed
Publication date2023
Number of pages84
QualificationMasters by Research
Awarding Institution
Award date15/02/2022
  • Lancaster University
<mark>Original language</mark>English


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.