  We intend to investigate separately the photospheric and circumstellar (CS)
magnetic field components in seven Herbig Ae stars. The study is based on
low-resolution (R ~ 2000 and 4000) spectropolarimetric data collected from 2003
to 2005 at the Very Large Telescope (ESO, Chile) with the multi-mode instrument
FORS1. We show that the spectropolarimetric results strongly depend on the
level of CS contribution to the stellar spectra. We have improved the
determination accuracy of magnetic fields up to the 7 sigma level in the two
Herbig Ae stars HD139614 and HD144432, observed in 2005 when these objects were
at a low level state of their CS activity. We have established that at a higher
level state of CS activity the polarisation signatures are related mainly to
the CS matter. The presence of CS polarisation signatures formed in the stellar
wind supports the assumption that the magnetic centrifuge is a principal
mechanism of wind acceleration. We conclude that the most effective way to
investigate the magnetism of Herbig Ae stars is to monitor their
spectropolarimetric behaviour at different states of CS activity. Obviously,
higher resolution spectropolarimetric observations would extend the sample of
spectral lines to be used for the measurements of magnetic fields at different
levels in the stellar atmosphere and CS envelope. Such observations will give a
more complete insight into the magnetic topology in Herbig Ae stars.
