Speaker
John Cowan
(University of Oklahoma)
Description
Abundance observations indicate the presence of
rapid-neutron capture (i.e., r-process) elements in
old Galactic halo and globular cluster stars. These
observations provide insight into the nature of the earliest
generations of stars in the Galaxy -- the progenitors of the
halo stars -- responsible for neutron-capture synthesis of
the heavy elements.
The large
star-to-star scatter observed in the abundances of
neutron-capture element/iron ratios at low metallicities --
which disappears with increasing metallicity or [Fe/H] --
suggests the formation of these heavy elements (presumably
from certain types of supernovae) was rare in the early
Galaxy. The stellar abundances also indicate a change from
the r-process to the slow neutron capture ( i.e.,
s-) process at higher metallicities in the Galaxy and
provide insight into Galactic chemical evolution. Finally,
the detection of thorium and uranium in halo and globular
cluster stars offers an independent age-dating technique
that can put lower limits on the age of the Galaxy, and
hence the Universe.
Author
John Cowan
(University of Oklahoma)
