  We present an analysis of spectral line bisector variations for a few stars
observed in the SARG high precision radial velocity planet survey, and discuss
their relationship with differential radial velocities. The spectra we consider
are the same used for determining radial velocities. The iodine cell lines
employed in the measurement of radial velocities were removed before bisector
analysis. The line bisectors were then computed from average absorption
profiles obtained by cross correlation of the stellar spectra with a mask made
from suitable lines of a solar catalog. Bisector velocity spans were then
determined: errors in these quantities compare well with theoretical
expectations based on resolution, S/N and line shape. The plot of bisector
velocity span against radial velocity was studied to search for correlations
between line asymmetries and radial velocity variations. A correlation was seen
for HD 166435 due to stellar activity, and for HD 8071B due to spectral
contamination by the companion. No correlation was seen for 51 Peg and rho CrB,
stars hosting planets. We conclude that this technique may be useful to
separate radial velocity variations due to barycenter motion from spurious
signals in spectra acquired with the iodine cell.
