Origin of the CEMP-no Group Morphology in the Milky Way. (arXiv:1904.02758v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yoon_J/0/1/0/all/0/1">Jinmi Yoon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beers_T/0/1/0/all/0/1">Timothy C. Beers</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tian_D/0/1/0/all/0/1">Di Tian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Whitten_D/0/1/0/all/0/1">Devin W. Whitten</a>
The elemental-abundance signatures of the very first stars are imprinted on
the atmospheres of CEMP-no stars, as various evidence suggests they are
bona-fide second-generation stars. It has recently been recognized that the
CEMP-no stars can be sub-divided into at least two groups, based on their
distinct morphology in the $A$(C)-[Fe/H] space, indicating the likely existence
of multiple pathways for their formation. In this work, we compare the halo
CEMP-no group morphology with that of stars found in satellite dwarf galaxies
of the Milky Way — a very similar $A$(C)-[Fe/H] pattern is found, providing
clear evidence that halo CEMP-no stars were indeed accreted from their host
mini-halos, similar in nature to those that formed in presently observed
ultra-faint dwarfs (UFDs) and dwarf spheroidal (dSph) galaxies. We also infer
that the previously noted “anomalous” CEMP-no halo stars (with high $A$(C) and
low [Ba/Fe] ratios) that otherwise would be associated with Group I may have
the same origin as the Group III CEMP-no halo stars, by analogy with the
location of several Group III CEMP-no stars in the UFDs and dSphs and their
distinct separation from that of the CEMP-$s$ stars in the $A$(Ba)-$A$(C)
space. Interestingly, CEMP-no stars associated with UFDs include both Group II
and Group III stars, while the more massive dSphs appear to have only Group II
stars. We conclude that understanding the origin of the CEMP-no halo stars
requires knowledge of the masses of their parent mini-halos, which is related
to the amount of carbon dilution prior to star formation, in addition to the
nature of their nucleosynthetic origin.
The elemental-abundance signatures of the very first stars are imprinted on
the atmospheres of CEMP-no stars, as various evidence suggests they are
bona-fide second-generation stars. It has recently been recognized that the
CEMP-no stars can be sub-divided into at least two groups, based on their
distinct morphology in the $A$(C)-[Fe/H] space, indicating the likely existence
of multiple pathways for their formation. In this work, we compare the halo
CEMP-no group morphology with that of stars found in satellite dwarf galaxies
of the Milky Way — a very similar $A$(C)-[Fe/H] pattern is found, providing
clear evidence that halo CEMP-no stars were indeed accreted from their host
mini-halos, similar in nature to those that formed in presently observed
ultra-faint dwarfs (UFDs) and dwarf spheroidal (dSph) galaxies. We also infer
that the previously noted “anomalous” CEMP-no halo stars (with high $A$(C) and
low [Ba/Fe] ratios) that otherwise would be associated with Group I may have
the same origin as the Group III CEMP-no halo stars, by analogy with the
location of several Group III CEMP-no stars in the UFDs and dSphs and their
distinct separation from that of the CEMP-$s$ stars in the $A$(Ba)-$A$(C)
space. Interestingly, CEMP-no stars associated with UFDs include both Group II
and Group III stars, while the more massive dSphs appear to have only Group II
stars. We conclude that understanding the origin of the CEMP-no halo stars
requires knowledge of the masses of their parent mini-halos, which is related
to the amount of carbon dilution prior to star formation, in addition to the
nature of their nucleosynthetic origin.
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