We present visible, near IR, and mm-wave observations of RCW 108, a molecular
cloud complex in the AraOB1 association that is being eroded by the energetic
radiation of two O-type stars in the nearby cluster NGC 6193. The western part
of the RCW108 cloud contains an embedded compact HII region, IRAS 16362-4845,
ionized by an aggregate of early-type stars. We notice a lack of stars later
than A0 in the aggregate and speculate that this might be a consequence of its
extreme youth. We examine the distribution of stars displaying IR excesses
projected across the molecular cloud. While many of them are located in the
densest area of the molecular cloud near IRAS16362-4845, we also find a group
concentrating towards the edge of the cloud that faces NGC 6193, as well as
some other stars beyond the edge of the molecular cloud. The intense ionizing
radiation field by the O stars in NGC6193 is a clear candidate trigger of star
formation in the molecular cloud, and we suggest that the existence and
arrangement of stars in this region of the cloud supports a scenario in which
their formation may be a consequence of this. However, IR excess stars are also
present in some areas of the opposite side of the cloud, where no obvious
candidate external trigger is identified. The existence of such tracers of
recent star formation scattered across the more massive molecular cloud
associated with IRAS 16362-4845, and the low star formation efficiency that we
derive, indicate that it is in a state to still form stars. This is in contrast
to the less massive cloud close to NGC 6193, which seems to be more evolved and
mostly already recycled into stars, and whose internal kinematics show hints of
having been perturbed by the presence of the massive stars formed out of it.Comment: Accepted for publication in Astronomy and Astrophysics, 25 pages,
paper with original figures available at
http://www.eso.org/~fcomeron/rcw108.ps.g
