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Chemical Abundances in Mercury-Manganese Stars

Over the past few of decades interest in HgMn stars has grown substantially. These stars offer a unique opportunity to test and confirm the theories of diffusion, accretion of super nova ejection and selective magnetic accretion from the interstellar medium.

Under supervision of Dr Mike Dworetsky, Alex Dyer has focussed his Master's project on the analysis of Strontium and Yttrium ratios in two dozen Mercury-Manganese stars. His research has contributed to the mounting evidence in favour of the diffusion model to explain the substantial excess in manganese in such stars as 53Tau.

Spectra of the stars were collected at the Lick observatory between 1994 and 1997. The data were reduced with DIPSO and IRAF and analysed using UCLSYN, a specialist program co-written by Dr Dworetsky himself. 450 line profiles were synthesised for the project and curves-of-growth of both Yttrium and Strontium abundances were examined.

Since the diffusion model's invention in 1970 it has evolved into a parameter free model for non-magnetic A and B stars. One of the main problems left for this parameter free models is: can it account for the vast diversity in elemental abundance for stars with very similar physical properties (effective temperature, rotational velocity and surface gravity) as seen throughout the HgMn Class?