The structure and dynamics of the Small Magellanic Cloud (SMC) remain poorly understood, despite the increased volume and quality of data that have become available in recent years. A fundamental question is the extent to which the dynamics of the SMC are influenced by its interaction with the Large Magellanic Cloud (LMC). Most of the kinematical studies to date concentrated on young stars and gas (see e.g. Torres & Carranza 1987 for a review; Mathewson et al. 1988), or they were limited to the central regions of the SMC. However, most of the gravitating mass of the SMC is associated with the intermediate-age and old populations. Therefore a complete understanding of the SMC dynamics and of the interaction between the LMC and the SMC requires kinematical studies of relatively old populations. Another reason for selecting old stars for such a study is that the kinematics of gas and young stars (formed from it) can be significantly affected by hydrodynamic processes. These may be associated both with interactions between the gaseous components of the two galaxies during a close encounter, and with the star formation mechanisms themselves, through the interactions of stellar winds and supernovae with the interstellar medium. The very complicated picture of the kinematical field in the SMC, arising from the latter processes, can be seen clearly in the new high resolution 21-cm hydrogen maps constructed by Staveley-Smith et al. (1995).
There have been four major studies of the
kinematics of older populations in the SMC published to date.
Hardy et al. (1989) derived radial velocities for a sample of 150
carbon stars located in the central 1-2 kpc
of the SMC.
They found no evidence for rotation or of velocity splitting in their sample.
Similar results had been found earlier by Dopita et al. (1985)
from a
study of the kinematics of 44 planetary nebulae lying mostly in the main body
of the SMC.
It is difficult however to extrapolate these results to the SMC as a whole,
the radial extent of which is >6 kpc in projection (see e.g.
Morgan & Hatzidimitriou 1995).
In the outer regions of the SMC there have
been two kinematical studies of old
stars. However, both were restricted to small regions, and contain relatively
small numbers of stars. Suntzeff et al. (1986)
derived the radial
velocities of 11 "halo'' giants located close to the star cluster NGC 121. There
was no evidence in their sample of a bimodal velocity distribution,
though the sample was too small for any firm results.
Hatzidimitriou et al. (1993) studied the radial velocity distribution
of a sample of 29 red horizontal-branch stars to the NE of
the SMC, distributed within a 40 arcmin field, at a projected distance of
kpc from the optical centre of the SMC. The sample was
located in a region of alleged large
depth along the line of sight (Hatzidimitriou & Hawkins 1989).
The data showed a well-defined correlation between
distance along the line of sight and radial velocity, which was tentatively
interpreted as the result of the tidal interaction between the LMC and the SMC.
This result is suggestive of disturbed dynamics along the line of
sight, at least in one particular direction.
It reinforces the usefulness of kinematical
studies of older stars in the outer parts of the SMC, where
the stars are less strongly bound to their parent galaxy and hence may be
more easily seen to reflect the gravitational
effects of the SMC-LMC interaction.
Nevertheless, it is obvious that kinematical information for much
larger samples of old stars distributed over larger areas is
necessary to understand properly the kinematics of the SMC.
Carbon stars are very well suited for this type of study: by being
easily found and unambiguously recognised they provide an
observationally well-defined sample;
astrophysically they belong to a reasonably well-understood
intermediate-age population and are often used as tracers of such
populations in nearby galaxies. In the
Magellanic Clouds in particular, carbon stars are sufficiently numerous
and bright to be particularly useful
for kinematical and dynamical studies.
It is important to note that the population of carbon stars in the SMC
maps closely the distribution of intermediate-age and old stars,
as can be seen by a comparison of their spatial distribution with
that of clump/red horizontal-branch stars, which are generally older
than 
Gyr (Gardiner & Hatzidimitriou 1992;
Morgan & Hatzidimitriou 1995)
and with that of RR Lyrae stars (Hatzidimitriou 1993).
In this paper, we present the kinematical study of a sample of 71 outlying carbon stars in the SMC. We also observed a small sample of 16 carbon star candidates in the LMC halo on the side nearest to the SMC. Sect. 2 describes the observations and reductions; in Sect. 3 the resulting radial velocities and their accuracy are presented, while in Sect. 4 we discuss the significance of the results.