Issue |
A&A
Volume 445, Number 3, January III 2006
|
|
---|---|---|
Page(s) | 979 - 998 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20053324 | |
Published online | 03 January 2006 |
Probing the formation of intermediate- to high-mass stars in protoclusters
A detailed millimeter study of the NGC 2264 clumps
1
CEA/DSM/DAPNIA, Service d'Astrophysique, CE Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France e-mail: [peretto;pandre]@cea.fr
2
AIM – Unité Mixte de Recherche CEA – CNRS – Université Paris VII – UMR 7158, France
3
Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received:
27
April
2005
Accepted:
24
August
2005
We present the results of dust continuum and molecular line observations
of two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, including
extensive mapping performed with the MAMBO bolometer array and the HERA
heterodyne array on the IRAM 30 m telescope. Both NGC 2264 clumps are located in
the Mon OB1 giant molecular cloud complex, adjacent to one another.
Twelve and fifteen compact millimeter continuum sources (i.e. MMSs) were
identified in clumps C and D, respectively.
These MMSs have larger sizes and masses than the millimeter continuum
condensations detected in well-known nearby protoclusters such as
ρ Ophiuchi.
The MMSs of NGC 2264 are closer in size
to the DCO+ “cores” of ρ Oph, although they are somewhat
denser and exhibit broader linewidths. Most of the MMSs of
NGC 2264-C harbor candidate Class 0 protostars associated
with shocked molecular hydrogen jets.
Evidence of widespread infall motions was found in, e.g.,
HCO+(3–2) or CS(3–2) in both NGC 2264-C and NGC 2264-D.
A sharp velocity discontinuity ~2 km s-1 in amplitude was observed
in N2H+(1–0) and H13CO+(1–0) in the central, innermost part
of NGC 2264-C, which we interpreted as the
signature of a strong dynamical interaction between two MMSs and their
possible merging with the central MMS C-MM3.
Radiative transfer modelling supports the idea that NGC 2264-C is
a highly unstable prolate clump in the process of collapsing
along its long axis on a near free-fall dynamical timescale ~ yr.
Our model fit of this large-scale collapse suggests
a maximum mass inflow rate
~
yr-1 toward the central
protostellar object C-MM3.
In NGC 2264-D, we estimated a mass infall rate
yr-1 toward the rotating Class 0
object D-MM1, also based on radiative transfer modelling of the
observations.
Such infall rates are sufficiently high to overcome radiation pressure
and allow the formation of ~
stars by accretion
in ~
yr, i.e., a time that is similar
to the global dynamical timescale of the central part of NGC 2264-C.
We conclude that we are likely witnessing the formation of a high-mass
(
) protostar in the central part of NGC 2264-C.
Our results suggest a picture of massive star formation intermediate
between the scenario of stellar mergers of Bonnell et al.
(1998) and the massive turbulent core model of McKee & Tan (2003),
whereby a turbulent, massive ultra-dense core is formed
by the gravitational merger of two or more Class 0 protostellar cores
at the center of a collapsing protocluster.
Key words: stars: formation / stars: circumstellar matter / ISM: clouds / ISM: molecules / ISM: kinematics and dynamics
© ESO, 2006
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