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.
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?