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Chemical abundances in normal and chemically peculiar AB stars

MSci student Rosie Willatt, under the supervision of Dr Mike Dworetsky, analysed spectroscopic data taken over 5 years by UCL astronomy students at OHP. These data were used to infer physical and chemical characteristics of target stars. Abundances of the noble gases were deduced in so-called mercury-manganese stars – objects with higher than normal amounts of those elements present. These stars offer a unique opportunity to test competing theories of diffusion, accretion of supernova ejecta, and selective magnetic accretion from the interstellar medium.

Read the Nuffield Foundation page on this project or the pre-print paper prepared by Rosie Willatt and Dr Mike Dworetsky for more information.

Alex Dyer focussed his Master's project on the analysis of Strontium and Yttrium ratios in two dozen Mercury-Manganese stars. He used pectra obtained at Lick Observatory, analysing them using UCLSYN, a specialist program co-written by Dr Dworetsky.

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. Since it was devised in 1970, the diffusion model has evolved into a parameter-free model for non-magnetic A and B stars. One of the main problems left 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?