The Search for Additional Ultra-Weak Magnetic Field A-type Stars and discovery of the Evolving Chemical Abundance Distributions in Alhena

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Hollett, Angelo
Among intermediate mass stars, only the chemically peculiar Ap/Bp stars have been historically found to be magnetic, with magnetic field strengths of a few hundred up to over 10 thousand gauss. In recent literature, a small number of early A type stars exhibiting magnetic field strengths of order 1 G or less have been reported. These ‘ultra-weak’ field stars are separated from their Ap/Bp counterparts by a so-called ‘magnetic desert’. The physical processes that give rise to ultra-weak field magnetism are still debated in literature. This is largely an issue of sample size, as only 5 ultra-weak field stars are currently known to exist. In an effort to continue the search for additional ultra-weak field stars, we derive a sample of intermediate mass stars that display similar observable qualities as previously detected ultra-weak field stars. We present the results of an observing proposal to ESPaDOnS at CFHT of the A star o Pegasi and report a constraint on the presence of an ultra-weak magnetic field. An outstanding member of our sample is the Am star Alhena, within the magnetic desert. We attempt to reproduce results of a previous study of this star, and in doing so uncover new evidence for evolving abundance distributions on time scales of a few years. We believe that this is the first instance of such behaviour observed in an Am or Ap star.
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