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tokens: The centres of the two groups projected on the sky are not very different. Given the low density and extended nature of the foreground population, it is possible that it extends beyond our field of view. The statistical parameters obtained for each group distribution ( d N and σ N of Model 2, see Table 1 ) suggest that the two groups are spatially separate. We consider the larger population to be the main Cygnus OB2 association (Group 2) and consider the foreground population to be a separate group approximately ∼400 pc in the foreground (Group 1). The distance of the foreground group of ∼1350 pc puts it at a similar distance to Cygnus-X as a whole (see Rygl et al. 2012 ) suggesting that the main part of Cygnus OB2 is actually behind Cygnus-X by several hundred parsecs (though the line-of-sight depth of Cygnus-X is not well constrained). Consequently, the main group is more distant than previously thought, and therefore its stellar content will both be more luminous (approximately 1.5 times more luminous compared to the estimates in Wright et al. 2015 ) and more massive. Interestingly, this puts the distance to the main part of Cygnus OB2 closer to that originally derived by Massey Thompson ( 1991 ). 5.2 The foreground group We have identified 19 stars in the foreground group ( of the sample), seven of them classified as O-type stars. The bright BD + 40 4212 double system ( G = 9.39 mag) is included in this group, as well as the star HD 195213 ( G = 8.38 mag). This group includes approximately 10 of the total population of O-type stars in Cygnus OB2, and thus its total mass can be estimated as a similar fraction of the total mass of 16 500 M ⊙ estimated by Wright et al. ( 2015 ), i.e. 1650 M ⊙ , similar to that of the Orion Nebula Cluster (although according to our results, the estimation by Wright et al. 2015 will have to be corrected upwards). We note that the foreground group is appreciably more dispersed on the sky than the main group. The proper motions also suggest it to be more diffuse and less likely to be a bound group. This could suggest that it is a part of older foreground population that extends further outside our field of view. However, a detailed study of the physical properties of its stellar content is needed to establish the most probable scenario. 5.3 Potential contaminants Here, we discuss the sources identified as probable foreground or background contaminants (Group 3) and not part of either the main Cyg OB2 population or the foreground group. Foreground contaminants : HD 196305 is a very luminous star and has a parallax that places it at a distance of pc, in agreement with previous studies that suggest it to be a foreground contaminant (Chentsov et al. 2013 ). CCDMJ20323 + 4152AB has been reported as a visual double star by Gili Bonneau ( 2001 ) and therefore its binary nature could be affecting the parallax. MT91-426 and MT-170 also appear as foreground sources, despite the fact that Wright et al. ( 2015 ) proposed them