All Figures

Figure 1: The space velocity of field O stars. Note that not all field O stars under study have Hipparcos proper motions. The peculiar tangential velocities of the field O stars are derived from Hipparcos propermotions. The uncertainty has been calculated by propagating a 30% uncertainty in the distance. Symbols are as follows: filled asterisks indicate absolute uncertainty less than 10 km s-1, filled circles an uncertainty between 10-20 km s-1, and empty circles >20 km s-1. Some field O stars have space velocities negligibly different from the bulk of the Galactic field. Five stars with clusters discussed in Paper I are encircled.

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In the text

Figure 2: Height above the Galactic plane (Z) as function of the galactic longitude for O field stars. The empty asterisks are suspected runaway stars from Table 2 and stars associated with clusters of Table 3. The five filled and encircled symbols have indication of a nearby cluster. All open circles indicate associations of OB stars within 3 kpc of the Sun from Mel'Nik & Efremov (1995). The size of each open circle is proportional to the estimated richness of the association.

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In the text

Figure 3: Both panels show the calculated cumulative distribution for the total number of stars per cluster (lower full curves) and the number of O-type stars per cluster (upper full curves). The simulations have been done for 2 stellar IMFs (see text), therefore there are 2 upper and 2 lower full curves, although the latter are hardly distinguishable. An O-type star in the simulation is a star more massive than . The dashed curves correspond to observed number fraction for Galactic OB-associations. The point with the errorbar corresponds to the observed number of Galactic field O-type stars, following the analysis in this paper. The left panel is for a CMF with slope and the right panel for . The right panel fits the observations.

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In the text