20,372 research outputs found
The Most Metal-Poor Stars. V. The CEMP-no Stars in 3D and Non-LTE
We explore the nature of carbon-rich ([C/Fe]_{1D,LTE} > +0.7), metal-poor
([Fe/H_{1D,LTE}] < -2.0) stars in the light of post 1D,LTE literature analyses,
which provide 3D-1D and NLTE-LTE corrections for iron, and 3D-1D corrections
for carbon (from the CH G-band, the only indicator at lowest [Fe/H]).
High-excitation C~I lines are used to constrain 3D,NLTE corrections of G-band
analyses. Corrections to the 1D,LTE compilations of Yoon et al. and Yong et al.
yield 3D,LTE and 3D,NLTE Fe and C abundances. The number of CEMP-no stars in
the Yoon et al. compilation (plus eight others) decreases from 130 (1D,LTE) to
68 (3D,LTE) and 35 (3D,NLTE). For stars with -4.5 < [Fe/H] < -3.0 in the
compilation of Yong et al., the corresponding CEMP-no fractions change from
0.30 to 0.15 and 0.12, respectively.
We present a toy model of the coalescence of pre-stellar clouds of the two
populations that followed chemical enrichment by the first zero-heavy-element
stars: the C-rich, hyper-metal-poor and the C-normal, very-metal-poor
populations. The model provides a reasonable first-order explanation of the
distribution of the 1D,LTE abundances of CEMP-no stars in the A(C) and [C/Fe]
vs. [Fe/H] planes, in the range -4.0 < [Fe/H] < -2.0.
The Yoon et al. CEMP Group I contains a subset of 19 CEMP-no stars (14% of
the group), 4/9 of which are binary, and which have large [Sr/Ba]_{1D,LTE}
values. The data support the conjectures of Hansen et al. (2016b, 2019) and
Arentsen et al. (2018) that these stars may have experienced enrichment from
AGB stars and/or "spinstars".Comment: ApJ in pres
Can the nuclear symmetry potential at supra-saturation densities be negative?
In the framework of an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU)
transport model, for the central Au+Au reaction at an incident
beam energy of 400 MeV/nucleon, effect of nuclear symmetry potential at
supra-saturation densities on the pre-equilibrium clusters emission is studied.
It is found that for the positive symmetry potential at supra-saturation
densities the neutron to proton ratio of lighter clusters with mass number
() is larger than that of the weighter clusters with
mass number (), whereas for the negative symmetry potential
at supra-saturation densities the is \emph{smaller} than that
of the . This may be considered as a probe of the negative
symmetry potential at supra-saturation densities.Comment: 5 pages, 3 figures, 1 table, to be publishe
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