Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Four open questions in massive star evolution   We discuss four questions dealing with massive star evolution. The first one
is about the origin of slowly rotating, non-evolved, nitrogen rich stars. We
propose that these stars may originate from initially fast rotating stars whose
surface has been braked down. The second question is about the evolutionary
status of alpha-Cygni variables. According to their pulsation properties, these
stars should be post red supergiant stars. However, some stars at least present
surface abundances indicating that they should be pre red supergiant stars. How
to reconcile these two contradictory requirements? The third one concerns the
various supernova types which are the end point of the evolution of stars with
initial masses between 18 and 30 Msun, i.e. the most massive stars which go
through a red supergiant phase during their lifetime. Do they produce types
IIP, IIL, IIn, IIb or Ib supernovae or do they end without producing any SN
event? Finally, we shall discuss reasons why so few progenitors of type Ibc
supernovae have yet been detected?

1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph