Speaker
Prof.
Anna Frebel
(Massachusetts Institute of Technology)
Description
We report the discovery of J0949-1617, the first bonafide CEMP-r+s
star identified. This class of objects has previously been suggested
to explain stars with neutron-capture element patterns that originate
from neither the r- or s-process alone. We find J0949-1617 to be a
CEMP stars with s-process enhancement that must have formed from gas
enriched by a prior r-process event. The light neutron-capture
elements follow a low-metallicity s-process pattern, while the heavier
neutron-capture elements above Eu follow an r-process pattern. The Pb
abundance is high, in line with an s-process origin. Thorium is also
detected, as expected from an r-process origin. We employ
nucleosynthesis model predictions that take an initial r-process
enhancement into account, and then determine the mass transfer of
carbon and s-process material from a putative, more massive companion
onto the observed star. The resulting abundances agree well with the
observed pattern. We speculate that J0949-1617 formed in an
environment similar to those of ultra-faint dwarf galaxies like Tucana
III and Reticulum II, which were enriched in r-process elements by one
or multiple neutron star mergers at the earliest times.
This star was found as part of the R-Process Alliance, a new effort to
uncover metal-poor halo stars with enhancements in neutron-capture
elements. We thus present the results of a high-resolution (R~35,000),
high signal-to-noise (S/N>200) Magellan/MIKE spectrum of the star RAVE
J094921.8-161722, a bright (V=11.3) metal-poor red giant star with
[Fe/H] = -2.2, identified as a carbon-enhanced metal-poor (CEMP) star
from the RAVE survey.
Primary author
Prof.
Anna Frebel
(Massachusetts Institute of Technology)
Co-authors
Alliance R-Process
(JINA)
Ms
Maude Gull
(MIT)