Statistical study of OB stars in NGC 6334 and NGC 6357

Russeil, D.; Zavagno, A.; Adami, C.; Anderson, L. D.; Bontemps, Sylvain; Motte, F.; Rodón, J. A.; Schneider, N.; Ilmane, A.; Murphy, K. J.

doi:10.1051/0004-6361/201117299

Cited by 48 publications

(66 citation statements)

References 66 publications

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“…This would have the underlying consequence of more massive objects accreting mass from larger regions than low-mass ones, favouring the models of large-scale global collapse of dense clumps. This is in line with recent results for the observed short timescales for IR-quiet dense clumps (Motte et al 2007;Russeil et al 2012) and for the dynamics at early stages in high-mass star-forming clumps (e.g., Schneider et al 2010;Csengeri et al 2011a,b), and more recently by Peretto et al (2013).…”

Section: Discussionsupporting

confidence: 91%

CO outflows from high-mass Class 0 protostars in Cygnus-X

Duarte-Cabral

Bontemps

Motte

et al. 2013

A&A

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Context. The earliest phases of the formation of high-mass stars are not well known. It is unclear whether high-mass cores in monolithic collapse exist or not, and what the accretion process and origin of the material feeding the precursors of high-mass stars are. As outflows are natural consequences of the accretion process, they represent one of the few (indirect) tracers of accretion. Aims. We aim to search for individual outflows from high-mass cores in Cygnus X and to study the characteristics of the detected ejections. We compare these to what has been found for the low-mass protostars, to understand how ejection and accretion change and behave with final stellar mass. Methods. We used CO (2-1) PdBI observations towards six massive dense clumps, containing a total of 9 high-mass cores. We estimated the bolometric luminosities and masses of the 9 high-mass cores and measured the energetics of outflows. We compared our sample to low-mass objects studied in the literature and developed simple evolutionary models to reproduce the observables. Results. We find that 8 out of 9 high-mass cores are driving clear individual outflows. They are therefore true equivalents of Class 0 protostars in the high-mass regime. The remaining core, CygX-N53 MM2, has only a tentative outflow detection. It could be one of the first examples of a true individual high-mass prestellar core. We also find that the momentum flux of high-mass objects has a linear relation to the reservoir of mass in the envelope, as a scale up of the relations previously found for low-mass protostars. This suggests a fundamental proportionality between accretion rates and envelope masses. The linear dependency implies that the timescale for accretion is similar for high-and low-mass stars. Conclusions. The existence of strong outflows driven by high-mass cores in Cygnus X clearly indicates that high-mass Class 0 protostars exist. The collapsing envelopes of these Class 0 objects have similar sizes and a similar fragmentation scale to the low-mass equivalents, and have enough mass to directly form high-mass stars from a monolithic collapse. If the pre-collapse evolution is quasistatic, the fragmentation scale is expected to limit the size of the initial mass reservoirs for all masses leading to higher densities at birth and therefore shorter free-fall times for higher mass stars. However, we find the collapse timescales to be similar for both lowand high-mass objects. This implies that in a quasi-static view, we would require significant turbulent/magnetic support to slow down the collapse of the more massive envelopes. But with this support still to be discovered, and based on independent indications of large dynamics in pre-collapse gas for high-mass star formation, we propose that such an identical collapse timescale implies that the initial densities, which should set the duration of the collapse, should be similar for all masses. Since the fragmentation scale is identical for all masses, a lower initial density requires that the mass that inc...

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Section: Discussionsupporting

confidence: 91%

CO outflows from high-mass Class 0 protostars in Cygnus-X

Duarte-Cabral

Bontemps

Motte

et al. 2013

A&A

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129

185

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“…The distance of NGC 6334, 1.74 kpc, has previously been derived by Persi & Tapia (2008) and confirmed by Russeil et al (2012) who found a distance of 1.75 kpc for the exciting stars of NGC 6334. We adopt 1.75 kpc throughout this paper.…”

Section: The Ngc 6334 Star-formation Complexsupporting

confidence: 79%

TheHerschelview of the massive star-forming region NGC 6334

Russeil

Schneider

Anderson

et al. 2013

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Aims. Fundamental to any theory of high-mass star formation are gravity and turbulence. Their relative importance, which probably changes during cloud evolution, is not known. By investigating the spatial and density structure of the high-mass star-forming complex NGC 6334 we aim to disentangle the contributions of turbulence and gravity. Methods. We used Herschel PACS and SPIRE imaging observations from the HOBYS key programme at wavelengths of 160, 250, 350, and 500 μm to construct dust temperature and column density maps. Using probability distribution functions (PDFs) of the column density determined for the whole complex and for four distinct sub-regions (distinguished on the basis of differences in the column density, temperature, and radiation field), we characterize the density structure of the complex. We investigate the spatial structure using the Δ-variance, which probes the relative amount of structure on different size scales and traces possible energy injection mechanisms into the molecular cloud. Results. The Δ-variance analysis suggests that the significant scales of a few parsec that were found are caused by energy injection due to expanding H ii regions, which are numerous, and by the lengths of filaments seen everywhere in the complex. The column density PDFs have a lognormal shape at low densities and a clearly defined power law at high densities for all sub-regions whose slope is linked to the exponent α of an equivalent spherical density distribution. In particular with α = 2.37, the central sub-region is largly dominated by gravity, caused by individual collapsing dense cores and global collapse of a larger region. The collapse is faster than free-fall (which would lead only to α = 2) and thus requires a more dynamic scenario (external compression, flows). The column density PDFs suggest that the different sub-regions are at different evolutionary stages, especially the central sub-region, which seems to be in a more evolved stage.

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“…3 confirms the visual impression that we are merely observing parts of a larger complex. Remarkably, the nearby region NGC 6334 also exhibits similar gas velocities and stellar photometry yields a similar distance (Russeil et al 2012). Therefore, NGC 6357 as a whole could be part of an even larger galactic complex.…”

Section: Distance To Pismis 24 and Extinctionmentioning

confidence: 64%

“…1). Several optical spectroscopic and photometric observations have unveiled a number of coeval (∼1 Myr) O-type stars among its members (Moffat & Vogt 1973;Neckel 1978;Lortet et al 1984;Massey et al 2001;Russeil et al 2012). The two brightest stars were identified as an O3 If (Pismis 24 1, a.k.a.…”

Section: Introductionmentioning

confidence: 99%

Young open clusters in the Galactic star forming region NGC 6357

Massi

Giannetti

Carlo

et al. 2014

A&A

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Context. NGC 6357 is an active star forming region with very young massive open clusters. These clusters contain some of the most massive stars in the Galaxy and strongly interact with nearby giant molecular clouds. Aims. We study the young stellar populations of the region and of the open cluster Pismis 24, focusing on their relationship with the nearby giant molecular clouds. We seek evidence of triggered star formation "propagating" from the clusters. Methods. We used new deep JHK s photometry, along with unpublished deep Spitzer/IRAC mid-infrared photometry, complemented with optical HST/WFPC2 high spatial resolution photometry and X-ray Chandra observations, to constrain age, initial mass function, and star formation modes in progress. We carefully examine and discuss all sources of bias (saturation, confusion, different sensitivities, extinction). Results. NGC 6357 hosts three large young stellar clusters, of which Pismis 24 is the most prominent. We found that Pismis 24 is a very young (∼1-3 Myr) open cluster with a Salpeter-like initial mass function and a few thousand members. A comparison between optical and infrared photometry indicates that the fraction of members with a near-infrared excess (i.e., with a circumstellar disk) is in the range 0.3-0.6, consistent with its photometrically derived age. We also find that Pismis 24 is likely subdivided into a few different subclusters, one of which contains almost all the massive members. There are indications of current star formation triggered by these massive stars, but clear age trends could not be derived (although the fraction of stars with a near-infrared excess does increase towards the Hii region associated with the cluster). The gas out of which Pismis 24 formed must have been distributed in dense clumps within a cloud of less dense gas ∼1 pc in radius. Conclusions. Our findings provide some new insight into how young stellar populations and massive stars emerge, and evolve in the first few Myr after birth, from a giant molecular cloud complex.

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Statistical study of OB stars in NGC 6334 and NGC 6357

Cited by 48 publications

References 66 publications

CO outflows from high-mass Class 0 protostars in Cygnus-X

CO outflows from high-mass Class 0 protostars in Cygnus-X

TheHerschelview of the massive star-forming region NGC 6334

Young open clusters in the Galactic star forming region NGC 6357

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