  Young A-type stars in the pre--main-sequence (PMS) evolutionary phase are
particularly interesting objects since they cover the mass range (1.5-4 solar
ma sses) which is most sensitive to the internal conditions inherited during
the protostellar phase. In particular, they undergo a process of thermal
relaxation from which they emerge as fully radiative objects contracting
towards the main sequence. A-type stars also show intense surface activity
(including winds, accretion, pulsations) whose origin is still not completely
understood, and infrared excesses related to the presence of circumstellar
disks and envelopes. Disks display significant evolution in the dust
properties, likely signalling the occurrence of protoplanetary growth. Finally,
A-type stars are generally found in multiple systems and small aggregates of
lower mass companions.
