We present an analysis of how bisectors of spectral lines
vary,
for a few stars
observed during the high-accuracy
radial-velocity planet survey ongoing
at the Telescopio Nazionale Galileo (TNG) using the
Galileo High Resolution
Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG),
and discuss their relation with differential radial velocities. The iodine cell
lines employed in the radial velocity measurements were used to improve the wavelength
calibration and then 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 determined and the run of bisector velocity span against radial velocity
was studied to search for correlations between line asymmetries and radial velocity
variations. We present an analysis of spectra of HD 216122B that show a slight contamination
likely to be due to a stellar companion, and an analysis of spectra of HD 76036A, a case where the
line bisectors are useful for improving the RV measurements. These systems are part of
a survey sample being observed with adaptive optics (AdOpt at the TNG since 2006) in an
attempt to visually resolve stellar companions.