Dust opacities in dense regions

Henning, Th.; Michel, Bernhard; Stognienko, R.

doi:10.1016/0032-0633(95)00003-n

Cited by 120 publications

(112 citation statements)

References 72 publications

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“…The dust mass opacity (including dust properties and gas-to-dust mass ratio) is likely to vary with density, temperature, and the evolutionary state of the emitting medium (Henning et al 1995). Models of dust in low-mass protostellar cores (e.g.…”

Section: Analysis and Resultsmentioning

confidence: 99%

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

Russeil¹,

Zavagno²,

Motte

et al. 2010

A&A

135

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Context. Our knowledge of high-mass star formation has been mainly based on follow-up studies of bright sources found by IRAS, and has thus been incomplete for its earliest phases, which are inconspicuous at infrared wavelengths. With a new generation of powerful bolometer arrays, unbiased large-scale surveys of nearby high-mass star-forming complexes now search for the high-mass analog of low-mass cores and class 0 protostars. Aims. Following the pioneering study of Cygnus X, we investigate the star-forming region NGC 6334-NGC 6357 (∼1.7 kpc). Methods. We study the complex NGC 6334-NGC 6357 in an homogeneous way following the previous work of Motte and collaborators. We used the same method to extract the densest cores which are the most likely sites for high-mass star formation. We analyzed the SIMBA/SEST 1.2 mm data presented in Munoz and coworkers, which covers all high-column density areas (A v ≥ 15 mag) of the NGC 6334-NGC 6357 complex and extracted dense cores following the method used for Cygnus X. We constrain the properties of the most massive dense cores (M > 100 M ) using new molecular line observations (as SiO, N 2 H + ,H 13 CO + , HCO + (1-0) and CH 3 CN) with Mopra and a complete cross-correlation with infrared databases (MSX, GLIMPSE, MIPSGAL) and literature. Results. We extracted 163 massive dense cores of which 16 are more massive than 200 M . These high-mass dense cores have a typical FWHM size of 0.37 pc, an average mass of M ∼ 600 M , and a volume-averaged density of ∼1.5 × 10 5 cm −3 . Among these massive dense cores, 6 are good candidates for hosting high-mass infrared-quiet protostars, 9 cores are classified as high-luminosity infrared protostars, and we find only one high-mass starless clump (∼0.3 pc, ∼4 × 10 4 cm −3 ) that is gravitationally bound. Conclusions. Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it provides a statistical estimate of the lifetime of massive stars. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their more well known high-luminosity infrared phase. As in Cygnus X, the statistical lifetime of high-mass protostars is shorter than found for nearby, low-mass star-forming regions which implies that high-mass pre-stellar and protostellar cores are in a dynamic state, as expected in a molecular cloud where turbulent and/or dynamical processes dominate.

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Section: Analysis and Resultsmentioning

confidence: 99%

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

Russeil¹,

Zavagno²,

Motte

et al. 2010

A&A

135

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“…The dust mass opacity (including dust properties and gasto-dust mass ratio) is likely to vary with density, temperature, and the evolutionary state of the emitting medium (Henning et al 1995). Models of dust in low-mass protostellar cores (e.g.…”

Section: Mass and Density Derived From Millimeter Continuum Mapsmentioning

confidence: 99%

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

Motte

Bontemps

Schilke

et al. 2007

A&A

327

722

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Aims. Our current knowledge of high-mass star formation is mainly based on follow-up studies of bright sources found by IRAS, and is thus biased against its earliest phases, inconspicuous at infrared wavelengths. We therefore started searching, in an unbiased way and in the closest high-mass star-forming complexes, for the high-mass analogs of low-mass pre-stellar cores and class 0 protostars. Methods. We have made an extensive 1.2 mm continuum mosaicing study of the Cygnus X molecular cloud complex using the MAMBO cameras at the IRAM 30 m telescope. The ∼ 3 • 2 imaged areas cover all the high-column density (A V ≥ 15 mag) clouds of this nearby (∼ 1.7 kpc) cloud complex actively forming OB stars. We then compared our millimeter maps with mid-infrared images, and have made SiO(2-1) follow-up observations of the best candidate progenitors of high-mass stars. Results. Our complete study of Cygnus X with ∼ 0.09 pc resolution provides, for the first time, an unbiased census of massive young stellar objects. We discover 129 massive dense cores (FWHM size ∼ 0.1 pc, M 1.2 mm = 4 − 950 M ⊙ , volume-averaged density ∼ 10 5 cm −3 ), among which ∼ 42 are probable precursors of high-mass stars. A large fraction of the Cygnus X dense cores (2/3 of the sample) remain undetected by the MSX satellite, regardless of the mass range considered. Among the most massive (> 40 M ⊙ ) cores, infrared-quiet objects are driving powerful outflows traced by SiO emission. Our study qualifies 17 cores as good candidates for hosting massive infrared-quiet protostars, while up to 25 cores potentially host high-luminosity infrared protostars. We fail to discover in the high-mass analogs of pre-stellar dense cores (∼ 0.1 pc, > 10 4 cm −3 ) in Cygnus X, but find several massive starless clumps (∼ 0.8 pc, 7 × 10 3 cm −3 ) that might be gravitationally bound. Conclusions. Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it gives the first statistical estimates of their lifetime. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their better-known high-luminosity infrared phase. The statistical lifetimes of high-mass protostars and pre-stellar cores (∼ 3 × 10 4 yr and < 10 3 yr) in Cygnus X are one and two order(s) of magnitude smaller, respectively, than what is found in nearby, low-mass star-forming regions. We therefore propose that high-mass pre-stellar and protostellar cores are in a highly dynamic state, as expected in a molecular cloud where turbulent processes dominate.

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“…Using a dust temperature of 40 K (following Gueth et al 1997), and a dust mass opacity of 0.01 cm 2 g −1 , as recommended by Henning et al (1995) for a gas-to-dust ratio of 100, we obtain a mass of the central compact source of ∼0.12 M , while the mass of the envelope is ∼1.08 M . Thus, the total (compact + extended) circumstellar mass is ∼1.2 M .…”

Section: Envelope Mass -From Continuum Emissionmentioning

confidence: 99%

L1157: Interaction of the molecular outflow with the Class 0 environment

Beltrán

Gueth

Guilloteau

et al. 2004

A&A

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Abstract. We present high angular resolution interferometric observations [ ] of the dust continuum at 2.7 and 1.3 mm, and of the HC 3 N (J = 12 → 11) and C 18 O (J = 2 → 1) emission around L1157-mm, a Class 0 object that drives a spectacular molecular outflow. The millimeter dust emission is clearly resolved into two components, a flattened compact source of ∼450 × 250 AU at 1.3 mm, and mass ∼0.1 M , plus an extended envelope of ∼3000 AU at 1.3 mm, and mass ∼1.1 M . The millimeter spectral index varies throughout the region, with the lower value found toward the compact protostar, possibly indicating grain growth in the denser regions. A strong interaction between the molecular outflow and the close protostellar environment is taking place and affects the structure of the innermost parts of the envelope. This is shown by the spatial coincidence between the molecular outflow and the dust (1.3 mm continuum) and HC 3 N emission: both tracers show structures associated to the edges of the outflow lobes. Basically, the global picture sketched for the Class 0 object L1157-mm by Gueth et al. (1997) is supported. We find possible evidence of infall, but we do not detect any velocity gradient indicative of a rotating circumstellar disk.

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Dust opacities in dense regions

Cited by 120 publications

References 72 publications

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

L1157: Interaction of the molecular outflow with the Class 0 environment

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