On the Origins of Heavy Element Anomalies in HgMn Stars

Details On the Origins of Heavy Element Anomalies in HgMn Stars On the Origins of Heavy Element Anomalies in HgMn Stars

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998baas...30..760p&link_type=abstract

American Astronomical Society Meeting, 191, #125.03

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The element mercury is overabundant, relative to solar system abundances, by as much as five orders of magnitude in most HgMn stars. Similar overabundances of platinum, gold, and thallium are found in a number of these stars. Several of these elements also show large isotope anomalies in the cooler HgMn stars, with mixtures weighted much more strongly towards the heavier stable isotopes than in standard mixtures. Nucleosynthesis explanations of these isotope anomalies appear implausible, and they are presumed to result from diffusive separation. While radiatively driven diffusion undoubtedly plays a key role in the creation of these extreme abundance and isotope anomalies, the detailed mechanisms by which they form remain obscure. Our radiative force calculations have shown that radiation pressure in the stellar atmosphere cannot by itself support the mercury or thallium abundances observed in cool HgMn stars. Other mechanisms, such as mass loss, mixing, light induced drift, or magnetic fields must also play an important role. We have made quantitative estimates of how several of these mechanisms might influence abundances and isotope separation. The magnetic fields required to affect atmospheric abundances appear to be substantially larger than allowed by existing observations. Light induced drift might be able to cause some isotope separation within a static distribution, but appears incapable of supporting the observed abundances. Mass loss rates would need to be > 10(-14) M_sun yr(-1) to support the observed mercury enhancement. Such a large mass loss rate would have profound implications for the origins of all abundance anomalies in HgMn stars.

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