1994A&A...285..640G

Measurements of interstellar absorption lines in the (1,0) band of the C₂ Phillips system, around 1.015 µm, are reported for the stars Nos. 12 and 5 of the Cyg OB2 association. The R(0), Q(2), and Q(4) lines, at a resolving power of 65,000, show a complex structure, with four discrete components in No. 12 and three in No. 5. The radial velocities of the various components, spread over a range of 22 km/s , agree in both stars, suggesting their origin in similar spatio-kinematic structures. The relative intensities between the various components are not the same in the two stars, but the net C₂ column densities derived for the two stars result nearly proportional to their respective B-V color excesses, as it has been found in stars of smaller reddening. A typical clump of absorbing gas, in the close neighborhood or within the association, has been characterized by an upper limit of 5 pc in linear dimensions and a mass of 200 M_☉. The low emission of the association in the free-free radio continuum is suggested to be a result of the removal of HII-gas by the powerful winds known to be emitted by its members.