Issue |
A&A
Volume 488, Number 3, September IV 2008
|
|
---|---|---|
Page(s) | 987 - 996 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:200809949 | |
Published online | 17 July 2008 |
A near-infrared survey of the entire R Coronae Australis cloud*
Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
Received:
11
April
2008
Accepted:
25
June
2008
Aims. To understand low- to intermediate-mass star-formation in the nearby R Cr A molecular cloud, we try to identify the stellar content that is accessible with near-infrared observations.
Methods. We obtained a JHKs band mosaic of ~ covering the entire R CrA molecular cloud with
unprecedented sensitivity. We present a catalogue of about 3500
near-infrared sources fainter than the saturation limit
mag, reaching
18 mag.
We analysed the extended sources by inspecting their
morphology and point sources by means of colour–colour and
colour–magnitude diagrams. Additionally, we compared the extinction
inferred from the NIR data with the line-of-sight dust emission at
1.2 mm. Sources towards high dust emission but relatively low
show a projected mm-excess; these sources are either
immediately surrounded by cold circumstellar material or,
if too red to be a true foreground object, they are embedded in the front
layer of the 1.2 mm emitting dust cloud.
In both cases they are most likely associated with
the cloud.
Results. By means of the projected mm-excess technique
we find 33 new faint near-infrared sources
deeply embedded in the Coronet cluster around R CrA,
for which so far about 20 bright infrared stars have been known.
In contrast to the Coronet region,
both the northwestern dust ridge and the southeastern
cloud condensation “C”
appear to be devoid of associated stars detectable with
our near-infrared data.
Furthermore, about
a dozen sources, which are spread over the entire molecular cloud region,
exhibit a possible K-band excess, but only
with marginal statistical significance (<), so that we do not
consider the indicated K-band excess as real.
Finally, while the
Herbig-Haro-like objects seen
on our maps are concentrated around the Coronet,
we find four new nebulae also located farther down to the southeast.
At the position of IRAS 18595-3712, an X-shaped bipolar nebula is
resolved; its exciting star is hidden behind an edge-on disc.
Conclusions. The deep near-infrared survey of the entire R CrA molecular cloud strengthens the evidence for the Coronet being the region where most of the young stars are found. Our results are consistent with earlier predictions that the R CrA cloud has fragmented into sub-condensations at different star-forming stages.
Key words: stars: formation / stars: pre-main sequence / stars: low-mass, brown dwarfs / infrared: stars
© ESO, 2008
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