Astronomy and Astrophysics – Astronomy
Scientific paper
May 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...202.2701h&link_type=abstract
American Astronomical Society Meeting 202, #27.01; Bulletin of the American Astronomical Society, Vol. 35, p.733
Astronomy and Astrophysics
Astronomy
Scientific paper
New optical MK classification spectra have been obtained for 14 OB star candidates identified by Comerón et al. (2002 A&A, 389, 874) and presumed to be possible members of the Cyg OB2 cluster as recently described by Knödlseder (2000 A&A, 360, 539). All 14 candidate OB stars observed are indeed early-type stars, strongly suggesting the remaining 31 candidates by Comerón et al. are also early-type stars. However, of these 14 new OB stars, as many as half appear to be older (in a more evolved evolutionary state) than the previously studied optical cluster, making their membership in Cyg OB2 doubtful. So while some of the newly identified OB stars may represent a more extended halo of the Cyg OB2 cluster, the survey of Comerón et al. also picked up a larger fraction of non-members. Presently, estimates of the very high mass of this cluster (total M ≈ 104 Msun and over 100 O stars) first made by Knödlseder remain higher than our study can support. Despite this, the recognition of Cyg OB2 being a more massive and extensive star cluster than previously realized using 2MASS images, along with the recently recognized super star cluster Westerlund 1 only a few kpc away (Clark & Negueruela 2002 A&A, 396, L25), reminds us that we are woefully under-informed about the massive star cluster population in our Galaxy. Radio surveys may not be detecting these massive clusters if they are more than a few million years old. Our best hope for remedying this shortfall is through deep infrared searches and follow up near-infrared spectroscopic observations, as was used to identify candidate members of the Cyg OB2 association. This program is supported by NSF grant AST-9973922 to the University of Cincinnati.
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