Martin, Alexander john (2017) Spectropolarimetric analysis of magnetic stars. Doctoral thesis, Keele University.

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Abstract

The spectra of Ap and Bp stars show evidence of non-homogenous distributions of chemical elements both vertically and horizontally, along with the presence of largescale ordered magnetic fields. The atomic diffusion theory in stellar atmospheres explains the presence of the non-homogenous element distributions as a result of the magnetic field’s effect on the radiative pressure in the photosphere. Recent modelling of the abundance distributions in Ap and Bp stars has questioned the results determined theoretically. In addition, there has been a debate over the uniqueness and reliability of
the results determined using Zeeman/Magnetic Doppler Imaging (Z/MDI). To provide the tools necessary to determine further observational constraints for diffusion theory and to check the uniqueness and reliability of current MDI measurements, this thesis presents the development of two codes: Sparti Simple for the analysis of spectra formed in non-magnetic stellar atmospheres; and Sparti for the analysis of Stokes IQUV profiles formed in magnetic stellar atmospheres.
Before the application of these two codes to observational data, testing was carried out to confirm the functionality and ability to cope with the challenges introduced as a result of the observation of Stokes IQUV profiles.
The analysis of non-magnetic stellar spectra is a first step in the analysis of magnetic stellar spectra and also provides important observational constraints to diffusion theory.
The member stars of the cluster NGC6250 were analysed using Sparti Simple as part of a larger collaborative effort to analyse the member stars of a variety of open
stellar clusters. A cluster membership analysis of the stars in NGC6250 was performed and the fundamental parameters and photospheric chemical abundances were determined for each of the 19 member stars. Finally, the magnetic roAp star HD24712 and Ap star HD137909 were analysed using Sparti to determine its ability to recover
unique and reliable results.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QB Astronomy
Divisions: Faculty of Natural Sciences > School of Geography, Geology and the Environment
Depositing User: Lisa Bailey
Date Deposited: 16 Mar 2017 10:55
Last Modified: 16 Mar 2017 10:55
URI: http://eprints.keele.ac.uk/id/eprint/3030

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