Issue |
A&A
Volume 433, Number 3, April III 2005
|
|
---|---|---|
Page(s) | 955 - 977 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20041586 | |
Published online | 29 March 2005 |
Star formation in RCW 108: Triggered or spontaneous?
1
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany e-mail: fcomeron@eso.org
2
I. Physikalische Institut, Universität Köln, 50937 Köln, Germany
3
OASU/Observatoire de Bordeaux, Université de Bordeaux I, 33270 Floirac Cedex, France e-mail: schneider@obs.u-bordeaux1.fr
4
OAMP, 2 place LeVerrier, 13004 Marseille, France e-mail: delphine.russeil@oamp.fr
Received:
2
July
2004
Accepted:
29
November
2004
We present visible, near infrared and mm-wave
observations of RCW 108, a molecular cloud complex in the Ara OB1
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 molecular cloud, for which we derive a mass of
~8000 , contains an embedded compact HII region,
IRAS 16362-4845, ionized by an aggregate of early-type stars for
which we estimate a mass of ∼210
. The spectral
type of the earliest star is O9, as confirmed by the visible
spectrum of the compact HII region. We notice a lack of stars
later than A0 in the aggregate, at least having the moderate
reddenings that are common among its B-type stars, and we
speculate that this might be a consequence of the extreme youth of
the aggregate. We also note the existence of a dense ionized clump
(
cm-3) appearing near the main ionizing star of
the compact HII region. We examine the distribution of stars
displaying infrared excesses projected across the molecular cloud.
While many of them are located in the densest (
cm-3)
area of the molecular cloud near the position of
IRAS 16362-4845, 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 NGC 6193 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
molecular cloud supports a scenario in which their formation may
be a consequence of this. However, infrared 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 (∼660
) 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.
Key words: ISM: HII regions / ISM: individual objects: RCW 108 / ISM: clouds / infrared: ISM
© ESO, 2005
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