2. Selection of targets
The proper motion of a star is related directly to the (total) tangential velocity by the well-known transformation
where K = 4.740. Thus, the detection of runaways with can be made out to for a nominal precision of at the level. Such is the case with Hipparcos, although more distant stars will often be fainter and have larger errors.
Guided by this, we first selected all Galactic WR stars from the catalogue of van der Hucht et al. (1981) with mag (slightly revised magnitudes are found in van der Hucht et al. 1988). This is a nice coincidence with the observability limit of the catalogue: . In actual fact, due to feasibility constraints of Hipparcos, only 67 WR stars were observed, which includes all Galactic WR stars down to , except: WR25 (at , one of 22 stars to ; this is unfortunate, since WR25 exhibits the largest X-ray flux known for any Galactic WR star); WR85, 92 (2 of 18 stars with ; this excludes WR43, the dense core of the cluster NGC 3603); WR12,30,75,93,143,152 (6 of 24 stars with ); and the addition of WR61, 121 (2 of 26 stars with ). These 67 stars are thus nearly complete to , and represent about one third of all presently known WR stars in the Galaxy (van der Hucht 1996).
A total of 66 O stars were selected from the catalogue of Cruz-Gonzalez et al. (1974), among the 72 stars with peculiar radial velocity components , after subtracting off the Solar motion and Galactic rotation according to their recipe. Six of these 72 stars were not observable with Hipparcos. This selection is nearly complete to mag, i.e. about two mags brighter than the WR sample.
© European Southern Observatory (ESO) 1998
Online publication: March 3, 1998