Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: WR20a: a massive cornerstone binary system comprising two extreme
  early-type stars   We analyse spectroscopic observations of WR20a revealing that this star is a
massive early-type binary system with a most probable orbital period of \sim
3.675 days. Our spectra indicate that both components are most likely of WN6ha
or O3If^*/WN6ha spectral type. The orbital solution for a period of 3.675 days
yields extremely large minimum masses of 70.7 \pm 4.0 and 68.8 \pm 3.8
M_{\odot} for the two stars. These properties make WR20a a cornerstone system
for the study of massive star evolution.

28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ