Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chemical composition of metal-poor stars in Coma Berenices ultra-faint
  dwarf galaxy as a proxy to individual chemical enrichment events   We present NLTE abundances and atmospheric parameters for three metal-poor
stars ([Fe/H]<-2) in Coma Berenices ultra-faint dwarf galaxy (UFD). The derived
results are based on new photometric observations obtained with the 2.5-m
telescope of the SAI MSU Caucasian observatory and spectra from the archive of
the 10-m Keck telescope. Effective temperatures were determined from V-I, V-K,
V-J colours. For each star, Teffs derived from different colours agree within
20K. Surface gravities (log g) were calculated using a relation between log g,
MV, BC, distance, Teff, and mass, adopted as 0.8MSun. The NLTE abundances for
Na, Mg, Ca, Ti, Fe, Ni, Sr, and Ba were determined. A revision of atmospheric
parameters and abundances, based on new photometric observations and accurate
modelling of spectral line formation resulted in reinterpretation of the star
formation history in Coma Berenices UFD. The derived chemical abundance
patterns for three stars differ from each other and from that, which is typical
for the MW halo stars of similar [Fe/H]. The S1 star shows solar [alpha/Fe] and
unprecedentedly low [Na/Mg] of -1.46, which is the lowest value among
metal-poor stars known to date. Abundance pattern of the S1 star is well
reproduced by nucleosynthesis model in metal-free massive stars explosion. The
stars S2 and S3, in contrast to S1, show high [alpha/Fe] ratios, for example,
[Mg/Fe]=0.8 in S2, while stars with -3.5<[Fe/H]<-2 in the other dwarf galaxies
and the MW show a typical ratio [Ca,Mg/Fe] of 0.3 dex. All the three stars show
low Sr and Ba abundances. These peculiarities in chemical composition argue for
a small number of nucleosynthesis events contributed to chemical abundances of
these stars. A wide range of metallicity, 0.65 dex, observed in Coma Berenices
is likely produced by inhomogeneous mixing of the interstellar medium, but not
an increase in [Fe/H] during a prolonged star formation.

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The categories of this paper are: q-fin
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an