Streaming motions of molecular clouds, ionized hydrogen, and OB stars in the Cygnus arm

The radial velocity fields of molecular clouds, OB stars, and ionized hydro gen in the Cygnus arm (l similar to 72 degrees -85 degrees) are analyzed. A gradient DeltaV(LSR)/Delta/ in the mean line-of-sight velocities of molecu lar clouds and ionized hydrogen due to differential Galactic rotation is de tected, and two groups of physically and genetically associated objects mov ing with different line-or-sight velocities are identified. One of the two molecular-cloud complexes (l similar to 77.3 degrees -80 degrees) is locate d within 1 kpc of the Sun, closer to the inner edge of the arm, whereas the other complex (l similar to 78.5 degrees -85 degrees) lies 1-1.5 kpc from the Sun and is farther from the inner edge of the arm. The residual azimuth al velocities of the objects in both groups are analyzed. The residual azim uthal velocities of the first molecular-cloud complex are directed opposite to the Galactic rotation (V- similar to -7 km/s), while those of the secon d complex are near zero or in the direction of Galactic rotation, independe nt of the distance to the complex (V- greater than or equal to 1 km/s). Lik e the molecular clouds, stars of the Cygnus arm form two kinematic groups w ith similar azimuthal velocities. On the whole, the mean azimuthal velociti es V- for the ionized hydrogen averaged over large areas agree with the vel ocities of either the hi-st or second molecular-cloud complex. In terms of density-wave theory, the observed differences between the magnitudes and di rections of the azimuthal velocities of the kinematic groups considered cou ld be due to their different locations within the arm. (C) 2001 MAIK "Nauka /Interperiodica".