Bibcode
Berlanas, S. R.; Herrero, A.; Comerón, F.; Pasquali, A.; Motta, C. Bertelli; Sota, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 612, id.A50, 20 pp.
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4
2018
Journal
Citations
30
Refereed citations
28
Description
Context. 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. Aim. 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,
using new intermediate resolution spectroscopy. Methods: We have
obtained intermediate resolution (R 5000) spectra for all of the
OB-type candidates between 2013 and 2017. We thus performed a spectral
classification of the sample using HeI-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. Results: From the whole
sample of 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. We have also obtained visual extinctions for all the new
confirmed massive OB members, placing them in a Hertzsprung-Russell
Diagram using calibrations for Teff and luminosity. Finally,
we have studied the age and extinction distribution of our sample within
the region. Conclusions: We have obtained new blue
intermediate-resolution spectra suitable for spectral classification of
61 OB candidates in Cygnus OB2 and surroundings. The confirmation of 42
new OB massive stars (earlier than B3) in the region allows us to
increase the young massive population known in the field. We have also
confirmed the correlation between age and Galactic longitude previously
found in the region. We conclude that many O and early B stars at B >
16 mag are still undiscovered in Cygnus.
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