Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-LTE calculations for neutral Na in late-type stars using improved
  atomic data   Neutral sodium is a minority species in the atmospheres of late-type stars,
and line formation in local thermodynamic equilibrium (LTE) is often a poor
assumption, in particular for strong lines. We present an extensive grid of
non-LTE calculations for several NaI lines in cool stellar atmospheres,
including metal-rich and metal-poor dwarfs and giants. For the first time, we
constructed a Na model atom that incorporates accurate quantum mechanical
calculations for collisional excitation and ionisation by electrons as well as
collisional excitation and charge exchange reactions with neutral hydrogen.
Similar to LiI, the new rates for hydrogen impact excitation do not affect the
statistical equilibrium calculations, while charge exchange reactions have a
small but non-negligible influence. The presented LTE and non-LTE
curves-of-growth can be interpolated to obtain non-LTE abundances and abundance
corrections for arbitrary stellar parameter combinations and line strengths.
The typical corrections for weak lines are -0.1...-0.2dex, whereas saturated
lines may overestimate the abundance in LTE by more than 0.5dex. The non-LTE Na
abundances appear very robust with respect to uncertainties in the input
collisional data.

23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics