Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New massive members of Cygnus OB2   The Cygnus complex is one of the most powerful star forming regions at a
close distance from the Sun (~1.4 kpc). Its richest OB association Cygnus OB2
is known to harbor many tens of O-type stars and hundreds of B-type stars,
providing a large homogeneous population of OB stars that can be analyzed. Many
studies of its massive population have been developed in the last decades,
although the total number of OB stars is still incomplete. Our aim is to
increase the sample of O and B members of Cygnus OB2 and its surroundings by
spectroscopically classifying 61 candidates as possible OB-type members of
Cygnus OB2. We have obtained new blue intermediate-resolution spectra suitable
for spectral classification of the 61 candidates in Cygnus OB2 and
surroundings. We thus performed a spectral classification of the sample using
He I-II and metal lines rates, as well as the Marxist Ghost Buster (MGB)
software for O-type stars and the IACOB standards catalog for B-type stars. Out
of the 61 candidates, we have classified 42 stars as new massive OB-type stars,
earlier than B3, in Cygnus OB2 and surroundings, including 11 O-type stars. The
other candidates are discarded as they display later spectral types
inconsistent with membership in the association. However, the magnitude cutoff
and dust extinction introduce an incompleteness. Many O and early B stars at B
> 16 mag are still undiscovered in the region. Finally, we have studied the age
and extinction distribution of our sample within the region, placing them in
the Hertzsprung-Russell Diagram using different stellar models in order to
assess age uncertainties. Massive star formation in Cygnus OB2 seems to have
proceeded from lower to higher Galactic longitudes, regardless of the details
of the models used. The correlation between age and Galactic longitude
previously found in the region is now confirmed.

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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: funct-an
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The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: hep-ph
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The categories of this paper are: q-alg
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin