R-associations. III. Local optical spiral structure

The galactic distribution of R-associations is investigated. They show that the local (Cygnus) spiral feature extends over 2 kpc in the direction of Vela (l approx. 265degree), and is clearly separated from the next inner (Carina--Sagittarius) spiral feature. There is some evidence for a concentration of the dust towards the inner edge of the local optical spiral feature, a phenomenon which is observed in external galaxies (Lynds 1970, 1972). The R-associations are combined with other good spiral tracers to produce a new map of optical spiral structure. A possible interpretation of this map is suggested in which the angle of inclination of the spiral arms is 13degreeplus-or-minus4degree