  The interpretation of X-ray detections from Herbig Ae/Be stars is disputed as
it is not clear if these intermediate-mass pre-main sequence stars are able to
drive a dynamo and ensuing phenomena of magnetic activity. Alternative X-ray
production mechanisms, related to stellar winds, star-disk magnetospheres, or
unresolved late-type T Tauri star companions have been proposed. In a series of
papers we have been investigating high-resolution X-ray Chandra images of
Herbig Ae/Be and main-sequence B-type stars to test the T Tauri hypothesis by
spatially resolving known visual companions from the primaries. Here we report
on six as yet unpublished Chandra exposures from our X-ray survey of Herbig
stars. The target list comprises six Herbig stars with known cool companions,
and three further A/B-type stars that are serendipitously in the Chandra
field-of-view. In this sample we record a detection rate of 100%, i.e. all
A/B-type stars display X-ray emission at levels of log(L_x/L_bol) ~ -5...-7.
The analysis of hardness ratios confirms that HAeBe's have hotter and/or more
absorbed X-ray emitting plasma than more evolved B-type stars. Radiative winds
are ruled out as exclusive emission mechanism on basis of the high X-ray
temperatures. Confirming earlier results, the X-ray properties of Herbig Ae/Be
stars are not vastly different from those of their late-type companion stars
(if such are known). The diagnostics provided by the presently available data
leave open if the hard X-ray emission of Herbig stars is due to young age or
indicative of further coronally active low-mass companion stars. In the latter
case, our detection statistics imply a high fraction of higher-order multiple
systems among Herbig stars.
