H<sub>2</sub>infrared emission and the formation of dense structures in the Orion molecular cloud

Vannier, L.; Lemaire, J. L.; Field, D.; Forêts, G. Pineau des; Pijpers, F. P.; Rouan, D.

doi:10.1051/0004-6361:20000258

Cited by 24 publications

(70 citation statements)

References 49 publications

(61 reference statements)

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“…This scenery may find support in the observations of GG, who showed that the emission of the CO P (8) line is unevenly distributed around Peak 1, and in the NICMOS image of the region (Stolovy et al 1998), showing a smallscale clumpy structure in the emission of the H 2 v = 1−0 S(1) line. A clumpy structure has been also observed by Vannier et al (2001) around Peak 2. Second, the possibility that a substantial fraction of hydrogen is in atomic form cannot be disregarded (see RBD).…”

Section: The Derived Beam-averaged N (Co) Of ≈6×10mentioning

confidence: 68%

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

González-Alfonso

Wright

Cernicharo³

et al. 2002

A&A

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Abstract. ISO/SWS observations of Orion Peak 1 and Peak 2 show strong emission in the ro-vibrational lines of CO v = 1−0 at 4.45-4.95 µm and of H2O ν2 = 1−0 at 6.3-7.0 µm. Toward Peak 1 the total flux in both bands is, assuming isotropic emission, ≈2.4 and ≈0.53 L , respectively. This corresponds to ≈14 and ≈3% of the total H2 luminosity in the same beam. Two temperature components are found to contribute to the CO emission from Peak 1/2: a warm component, with T k = 200-400 K, and a hot component with T k ∼ 3 × 10 3 K. At Peak 2 the CO flux from the warm component is similar to that observed at Peak 1, but the hot component is a factor of ≈2 weaker. The H2O band is ≈25% stronger toward Peak 2, and seems to arise only in the warm component. The P -branch emission of both bands from the warm component is significantly stronger than the R-branch, indicating that the line emission is optically thick. Neither thermal collisions with H2 nor with H I seem capable of explaining the strong emission from the warm component. Although the emission arises in the postshock gas, radiation from the most prominent mid-infrared sources in Orion BN/KL is most likely pumping the excited vibrational states of CO and H2O. CO column densities along the line of sight of N(CO) = 5-10×10 18 cm −2 are required to explain the band shape, the flux, and the P -R-asymmetry, and beam-filling is invoked to reconcile this high N(CO) with the upper limit inferred from the H2 emission. CO is more abundant than H2O by a factor of at least 2. The density of the warm component is estimated from the H2O emission to be ∼2 × 10 7 cm −3 . The CO emission from the hot component is neither satisfactorily explained in terms of non-thermal (streaming) collisions, nor by resonant scattering. Vibrational excitation through collisions with H2 for densities of ∼3 × 10 8 cm −3 or, alternatively, with atomic hydrogen, with a density of at least 10 7 cm −3 , are invoked to explain simultaneously the emission from the hot component and that from the high excitation H2 lines in the same beam. A jump shock is most probably responsible for this emission. The emission from the warm component could in principle be explained in terms of a C-shock. The underabundance of H2O relative to CO could be the consequence of H2O photodissociation, but may also indicate some contribution from a jump shock to the CO warm emission.

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Section: The Derived Beam-averaged N (Co) Of ≈6×10mentioning

confidence: 68%

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

González-Alfonso

Wright

Cernicharo³

et al. 2002

A&A

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“…Molecular densities are derived from analyses of near-infrared excitation and extinction, as well as being inferred from flux levels. Derived molecular densities range from 10 4 cm −3 in outflows from lowmass protostars like HH 111 to above 10 6 cm −3 in the OMC-1 outflow (Nisini et al 2002a;Vannier et al 2001). The density is critical in determining the cooling length behind the shock and this, subsequently, controls the nature of the flow (Blondin et al 1990).…”

Section: Introductionmentioning

confidence: 99%

Numerical simulations of highly collimated protostellar outflows

Rosén

Smith

2003

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Abstract. We present three-dimensional hydrodynamic simulations of jets as a model for protostellar outflows. We investigate molecular jets which are initially heavier, equal or lighter than a uniform ambient molecular medium, as well as a ballistic atomic jet, with the aim of distinguishing the resulting structures and relating them to various proposed protostellar evolutionary stages. We modify the ZEUS numerical code, to include time-dependent molecular hydrogen chemistry, a limited equilibrium C and O chemistry, and a detailed cooling function. We find highly focussed and accelerated flow patterns for outflows driven by molecular jets, caused by the combined strong cooling, small imposed jet shear and precession. We also find shoulders in the interface with associated shocks visible in our simulated near-infrared H 2 images. The shoulder location relative to the front of the bow shock distinguishes the relative density. Apart from this, the outflow structures are quite similar provided the jet is molecular. The ratio of jet power to H 2 1-0 S(1) line luminosity (increasingly required to interpret observations), is generally in the range 80-600. Sub-millimetre CO properties, including a velocity-position and velocity-channel diagram; are presented. We compare mass-velocity relationships derived directly and via the simulated CO data: significant systematic differences are uncovered. For the future, we identify fine-scale structure in the rotational CO 2-1 and CO 14-13 rotational lines which can be resolved with the millimetre array ALMA and the Herschel (FIRST) Observatory. We identify highly collimated outflows in the near-infrared that can be interpreted by this model.

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“…Self-similarity and lack of characteristic scale in molecular clouds must however break down at some dimension or range of dimensions associated with star formation, as demonstrated in Vannier et al (2001) and Gustafsson et al (2006). Turbulence creates local clumps of gas and this process, known as turbulent fragmentation, is considered the root cause of observed density structure and may give rise to large density contrasts.…”

Section: Introductionmentioning

confidence: 99%

“…For example, four different methods were used in Vannier et al (2001) in order to demonstrate that self-similarity breaks down at star-forming scales of around 500-1000 AU in a small portion of the Orion Molecular Cloud (OMC1). The present contribution should be seen in this light, not as a panacea for structure identification but rather as another tool for this purpose.…”

Section: Introductionmentioning

confidence: 99%

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A method for detection of structure

Gustafsson¹,

Lemaire

Field³

2006

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Context. In order to understand the evolution of molecular clouds it is important to identify the departures from self-similarity associated with the scales of self-gravity and the driving of turbulence. Aims. A method is described based on structure functions for determining whether a region of gas, such as a molecular cloud, is fractal or contains structure with characteristic scale sizes. Methods. Using artificial data containing structure it is shown that derivatives of higher order structure functions provide a powerful way to detect the presence of characteristic scales should any be present and to estimate the size of such structures. The method is applied to observations of hot H 2 in the Kleinman-Low nebula, north of the Trapezium stars in the Orion Molecular Cloud, including both brightness and velocity data. The method is compared with other techniques such as Fourier transform and histogram techniques. Results. It is found that the density structure, represented by H 2 emission brightness in the K-band (2-2.5 µm), exhibits mean characteristic sizes of 110, 550, 1700 and 2700 AU. The velocity data show the presence of structure at 140, 1500 and 3500 AU. Compared with other techniques such as Fourier transform or histogram, the method appears both more sensitive to characteristic scales and easier to interpret.

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H₂infrared emission and the formation of dense structures in the Orion molecular cloud

Cited by 24 publications

References 49 publications

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

Numerical simulations of highly collimated protostellar outflows

A method for detection of structure

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H2infrared emission and the formation of dense structures in the Orion molecular cloud

Cited by 24 publications

References 49 publications

CO and H2O vibrational emission toward Orion Peak 1 and Peak 2

CO and H2O vibrational emission toward Orion Peak 1 and Peak 2

Numerical simulations of highly collimated protostellar outflows

A method for detection of structure

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H₂infrared emission and the formation of dense structures in the Orion molecular cloud

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2