  Since 1999, we have been conducting a radial velocity survey of 179 K giants
using the CAT at UCO/Lick observatory. At present ~20-100 measurements have
been collected per star with a precision of 5 to 8 m/s. Of the stars monitored,
145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43
exhibit significant periodicities. Our aim is to investigate possible
mechanism(s) that cause these observed RV variations. We intend to test whether
these variations are intrinsic in nature, or possibly induced by companions, or
both. In addition, we aim to characterise the parameters of these companions. A
relation between log g and the amplitude of the RV variations is investigated
for all stars in the sample. Furthermore, the hypothesis that all periodic RV
variations are caused by companions is investigated by comparing their inferred
orbital statistics with the statistics of companions around main sequence
stars. A strong relation is found between the amplitude of the RV variations
and log g in K giant stars, as suggested earlier by Hatzes & Cochran (1998).
However, most of the stars exhibiting periodic variations are located above
this relation. These RV variations can be split in a periodic component which
is not correlated with log g and a random residual part which does correlate
with log g. Compared to main-sequence stars, K giants frequently exhibit
periodic RV variations. Interpreting these RV variations as being caused by
companions, the orbital param eters are different from the companions orbiting
dwarfs. Intrinsic mechanisms play an important role in producing RV variations
in K giants stars, as suggested by their dependence on log g. However, it
appears that periodic RV variations are additional to these intrinsic
variations, consistent with them being caused by companions.
