  We report the results of our radial-velocity monitoring of spectroscopic
binary systems in a sample of X-ray sources from the ROSAT All Sky Survey south
of the Taurus-Auriga star-forming region. The original sample of approximately
120 sources by Neuhaeuser et al. was selected on the basis of their X-ray
properties and the visual magnitude of the nearest optical counterpart, in such
a way as to promote the inclusion of young objects. Roughly 20% of those
sources have previously been confirmed to be very young. We focus here on the
subset of the original sample that shows variable radial velocities (43
objects), a few of which have also been flagged previously as being young. New
spectroscopic orbits are presented for 42 of those systems. Two of the
binaries, RXJ0528.9+1046 and RXJ0529.3+1210, are indeed weak-lined T Tauri
stars likely to be associated with the Lambda Orionis region. Most of the other
binaries are active objects of the RS CVn-type, including several W UMa and
Algol systems. We detect a strong excess of short-period binaries compared to
the field, and an unusually large fraction of double-lined systems, as well as
an overall high frequency of binaries out of the original sample. These results
can be understood as selection effects. A short description of the physical
properties of each binary is provided, and a comparison with evolutionary
tracks is made using the stellar density as a distance-independent measure of
evolution (abridged).
