  We are investigating the magnetic characteristics of pre-main sequence Herbig
Ae/Be stars, with the aim of (1) understanding the origin and evolution of
magnetism in intermediate-mass stars, and (2) exploring the influence of
magnetic fields on accretion, rotation and mass-loss at the early stages of
evolution of A, B and O stars. We have begun by conducting 2 large surveys of
Herbig Ae/Be stars, searching for direct evidence of photospheric magnetic
fields via the longitudinal Zeeman effect. From observations obtained using
FORS1 at the ESO-VLT and ESPaDOnS at the Canada-France-Hawaii Telescope, we
report the confirmed detection of magnetic fields in 4 pre-main sequence A- and
B-type stars, and the apparent (but as yet unconfirmed) detection of fields in
2 other such stars. We do not confirm the detection of magnetic fields in
several stars reported by other authors to be magnetic: HD 139614, HD 144432 or
HD 31649. One of the most evolved stars in the detected sample, HD 72106A,
shows clear evidence of strong photospheric chemical peculiarity, whereas many
of the other (less evolved) stars do not. The magnetic fields that we detect
appear to have surface intensities of order 1 kG, seem to be structured on
global scales, and appear in about 10% of the stars studied. Based on these
properties, these magnetic stars appear to be pre-main sequence progenitors of
the magnetic Ap/Bp stars.
