Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nitrogen isotopes in AGB carbon stars and presolar SiC grains: a
  challenge for stellar nucleosynthesis   Isotopic ratios of C, N, Si, and trace heavy elements in presolar SiC grains
from meteorites provide crucial constraints to nucleosynthesis. A long-debated
issue is the origin of the so-called A+B grains, as for them no stellar
progenitor has so far been clearly identified on observational grounds. We
report the first spectroscopic measurements of 14N/15N ratios in Galactic
carbon stars of different spectral types and show that J- and some SC-type
stars might produce A+B grains, even for 15N enrichments previously attributed
to novae. We also show that most mainstream (MS) grains are compatible with the
composition of N-type stars, but might also descend, in some cases, from SC
stars. From the theoretical point of view, no astrophysical scenario can
explain the C and N isotopic ratios of SC, J and N-type carbon stars together,
as well as those of many grains produced by them. This poses urgent questions
to stellar physics.

11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
25
The categories of this paper are: patt-sol