New optical MK classification spectra have been obtained for 14 OB star candidates identified by Comerón et al .
( 2002 ) and presumed to be possible members of the Cyg OB2 cluster as recently described by Knödlseder ( 2000 ) .
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 .
A thorough investigation of the properties of these new candidate members compared to the properties of the Cyg OB2 cluster star have been completed , using traditional as well as newly revised effective temperature scales for O stars .
The cooler O-star , effective temperature scale of Martins et al .
( 2002 ) gives a very close distance for the cluster ( DM = 10.4 ) .
However , even using traditional effective temperature scales , Cyg OB2 appears to be slightly closer ( DM = 10.8 ) than previous studies determined ( DM = 11.2 ; Massey & Thompson 1992 ) , when the very young age of the stellar cluster ( \sim 2 x 10 ^ { 6 } yrs ) is taken into account in fitting the late-O and early-B dwarfs to model isochrones .
Of the 14 new OB stars observed for this study , as many as half appear to be significantly older than the previously studied optical cluster , making their membership in Cyg OB2 suspect .
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 large fraction of non-members .
Presently , estimates of the very high mass of this cluster ( M _ { cl } \approx 10 ^ { 4 } M _ { \odot } and over 100 O stars ) first made by Knödlseder ( 2000 ) remain higher than this 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 candidate super star cluster Westerlund 1 only a few kpc away ( Clark & Negueruela 2002 ) , reminds us that we are woefully under-informed about the massive cluster population in our Galaxy .
Extrapolations of the locally derived cluster luminosity function indicate 10s to perhaps 100 of these very massive open clusters ( M _ { cl } \approx 10 ^ { 4 } M _ { \odot } , M _ { V } \approx - 11 ) should exist within our galaxy .
Radio surveys will not detect 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 by Comeron et al .
( 2002 ) to identify candidate members of the Cyg OB2 association .