Tracing the outer galactic halo with Blue Horizontal Branch stars

Titulaer, Lei (2021) Tracing the outer galactic halo with Blue Horizontal Branch stars. Bachelor's Thesis, Astronomy.

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Abstract

We present a new method to select Blue Horizontal Branch (BHB) stars from a sample of A-stars. BHB stars are used as standard candles to trace outward into the galactic halo, but in order to use them as such they need to be distinguished from contaminating Blue Straggler (BS) stars that have similar temperatures. Firstly, the method presented by Starkenburg et al. (2019) is applied to a new, larger sample of stars. The wide-field SDSS ugr-bands and the narrow-band Pristine CaHK-band are used to separate the BHB sequence from the BS sequence in the u−CaHK, g−r color-color space. We then extend the method and use the deeper CFIS u-band in combination with Pan-STARRS gr-bands and Pristine CaHK-band in order to be able to improve the selection of stars at distances further out. From the inferred heliocentric distances of the sample of BHB stars we are able to identify multiple known substructures and globular clusters in the halo. The Sagittarius stream is analysed and we are able to detect a recently discovered outward ‘spur’ feature by Sesar et al. (2017). The density profile of the ‘smooth’ component of the galactic halo is modelled by fitting a negative power law. This improves the result by Starkenburg et al. (2019) for the ‘smooth’ halo component. Using the new method utilising the CFIS u-band, we are not able to necessarily probe deeper into the halo, but we demonstrate that the completeness at distances over ∼ 75 kpc is largely improved, providing a clearer picture of the halo substructure in the 75 − 120 kpc regime.

Item Type:	Thesis (Bachelor's Thesis)
Supervisor name:	Starkenburg, E.
Degree programme:	Astronomy
Thesis type:	Bachelor's Thesis
Language:	English
Date Deposited:	23 Aug 2021 12:51
Last Modified:	25 Aug 2021 16:47
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/25625

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