Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: R4 and its circumstellar nebula: evidence for a binary merger?   We present new, NTT longslit spectroscopy of the B[e] supergiant in the
binary system R4 in the Small Magellanic Cloud. The data show extended,
forbidden N and S emissions which are typical signatures of circumstellar
matter. Their extension along the space axis of the slit defines an angular
size of 8.6'' which translates into a linear size of 2.4 pc. The N emission
lines also show the velocity structure of a bipolar outflow expanding at 100
km/s on average. This implies that, for a measured radius of 1.2 pc, the
outflow originated about 12000 yrs ago. The line flux ratio [NII]6584/[SII]6717
indicates that the nebula is nitrogen enriched and therefore it has been
ejected from the central star. This is the first bipolar, ejection nebula
detected around a well-established B[e] supergiant. The bipolar morphology and
the chemical enrichment shown by the nebula associated with R4 are consistent
with the picture of a binary merger (Langer & Heger 1998), in which R4 was
originally a system composed by a close pair and a third star (the observed A
companion). The close pair merged into a single star and the merging process
produced a circumstellar nebula that was later shaped by the ensueing B star
wind.

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The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci