4 Radial velocities

Our observed radial velocities are listed in Table 7 (Col. 5) and correspond to the median point of the 21-cm line profile measured at 20% level of maximum intensity. 540 of these measurements have been made in velocity search mode (see Fouqué et al. 1990); part of them has been already published in two previous papers (Bottinelli et al. 1992, 1993). For the other 1572 velocities, we have used the existing published data to "sight'' directly the appropriate frequency band.

The internal mean error on V₂₀ is calculated according to Fouqué et al. 1990 as follows:

$$\sigma(V_{20}) = \frac{4 \cdot (R \cdot \alpha)^{1/2}}{S/N}$$

where R is the actual spectral resolution, $\alpha = (W_{20}-W_{50})/2$ is the slope of the line profile, and S/N is the signal to noise ratio. The average of $\sigma (V_{20})$ is about 8 km s^-1.