Rotational excitation of SiO by collisions with helium

Dayou, Fabrice; Balança, Christian

doi:10.1051/0004-6361:20065718

Cited by 75 publications

(102 citation statements)

References 52 publications

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“…The set of equations is solved by means of a simple lambda-iteration, that stops when the relative difference between each of the level populations computed in two successive iterations drops below a convergence value of 10 −4 . The set of collisional rate coefficients for SiO with H 2 as a collision partner is simply scaled by the square root of the reduced mass ratio from the SiO-He rate coefficients calculated by Dayou & Balança (2006). The LVG code also provides the integrated intensity over the whole shock model for all transitions considered.…”

Section: Modelling Resultsmentioning

confidence: 99%

Revisiting the shocks in BHR71: new observational constraints and H₂O predictions forHerschel

Giannini

Flower

Parise

et al. 2011

A&A

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Context. During the formation of a star, material is ejected along powerful jets that impact the ambient material. This outflow phenomenon plays an important role in the regulation of star formation. Understanding the associated shocks and their energetic effects is therefore essential to the study of star formation. Aims. We present comparisons of shock models with observations of H 2 and SiO emission in the bipolar outflow BHR71. Such comparisons constitute a good way to constrain the type, velocity and age of the shock waves operating in this environment, as well as the physical conditions in the pre-shock region, e.g. density and magnetic field. They also provide a method for studying silicon in shocked regions. We make use of all the preliminary physical constraints obtained through such comparisons to predict water emission, under the basic assumption that the emission regions of the considered species coincide, at the resolution of currently available observations. Methods. New SiO observations from APEX are presented, and combined with Spitzer and ground-based observations of H 2 to constrain shock models. The shock regions associated with targeted positions in the molecular outflow are studied by means of a code that generates one-dimensional models of the propagation of stationary shock waves, and approximations to non-stationary ones. The emission of H 2 is dealt with in the code, whereas the emission of SiO and H 2 O are calculated by means of an external module, based on the LVG approximation. This external code provides local and integrated intensities for the lines of these species. A grid of models is used, covering shock velocities in the range 10 ≤ s ≤ 35 km s −1 , and pre-shock gas densities 10 4 ≤ n H ≤ 10 6 cm −3 . The magnetic field strength varies from about 45 μG to 600 μG. Results. The SiO emission in the inner part of the outflow is concentrated near the apex of the corresponding bow-shock that is also seen in the pure rotational transitions of H 2 . Simultaneous modelling is possible for H 2 and SiO and leads to constraints on the silicon pre-shock distribution on the grain mantles and/or cores. The best-fitting models are found to be of the non-stationary type, but the degeneracy of the solutions is still large. Pre-shock densities of 10 4 and 10 5 cm −3 are investigated, and the associated best-model candidates have rather low velocity (respectively, 20−30 and 10−15 km s −1 ) and are not older than 1000 years. We provide emission predictions for water, focusing on the brightest transitions, to be observed with the PACS and HIFI instruments of the Herschel Telescope.

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Section: Modelling Resultsmentioning

confidence: 99%

Revisiting the shocks in BHR71: new observational constraints and H₂O predictions forHerschel

Giannini

Flower

Parise

et al. 2011

A&A

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“…Collisional rates are then needed for each species to derive the physical conditions. For SiO previous calculations by Green and collaborators (Bieniek & Green 1983;Turner et al 1992; see http://www.giss.nasa.gov/ data/mcrates#sio) have provided collisional rates for this molecule and temperatures 20−1500 K. These collisional rates have been recalculated using a new SiO-p-H 2 surface by Dayou & Balança (2006). However, no collisional rates were available of SiS until recently: Vincent et al (2007) and have calculated the state-to-state collisional rates for the system SiS-He and SiS-H 2 , respectively.…”

Section: Discussionmentioning

confidence: 99%

A line-confusion limited millimeter survey of Orion KL

Tercero

Vincent

Cernicharo

et al. 2011

A&A

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Aims. We present a study of the silicon-bearing species detected in a line-confusion limited survey towards Orion KL performed with the IRAM 30-m telescope. The analysis of the line survey is organized by families of molecules. Our aim is to derive physical and chemical conditions for each family taking all observed lines into account from all isotopologs of each species. The large number of transitions in different vibrationally excited states covered by our data, which range from 80 to 280 GHz, let us provide reliable source-average column densities (hence, isotopolog abundances and vibrational temperatures) for the detected molecules. In addition, we provide a wide study of the physical properties of the source based on the different spectral components found in the emission lines. Methods. We modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between large velocity gradient (LVG) and local thermodynamic equilibrium (LTE) approximations depending on the physical conditions of the gas. We used appropriate collisional rates for the LVG calculations. To qualitatively investigate the origin of the SiS and SiO emissions in Orion KL we ran a grid of chemical models.Results. For the v = 1 state of SiO, we detected the J = 2−1 line and, for the first time in this source, emission in the J = 4−3 transition, both of them showing a strong masering effect. For SiO v = 0, we detected 28 SiO, 29 SiO, and 30 SiO; in addition, we have mapped the J = 5−4 SiO line. For SiS, we have detected the main species, 29 SiS, and SiS v = 1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of 15.5 km s −1 . A study of the 5−4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive an SiO/SiS column density ratio of 13 in the plateau component, four times lower than the cosmic O/S ratio 48. In addition, we provide upper limits to the column density of several non-detected silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of sulfur with silicon.

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“…The SiO(5-4) profiles reveal extremely high brightness temperatures T MB of up to 90 K. These values are compared with the result of the RADEX 7 non-LTE code (van der Tak et al 2007) with the rate coefficients for collisions with H 2 (Dayou & Balança 2006) using a plane parallel geometry, and assuming a FWHM linewidth of 20 km s −1 . One line is obviously not enough for a proper analysis; nevertheless, if we assume T kin ≤ 500 K, the high T MB values constrain the total SiO column densities N SiO ≥ 10 15 cm −2 .…”

Section: High Brightness Temperatures and Excitation Conditionsmentioning

confidence: 96%

First results from the CALYPSO IRAM-PdBI survey

Codella

Maury

Gueth

et al. 2014

A&A

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Context. The earliest evolutionary stages of low-mass protostars are characterised by hot and fast jets which remove angular momentum from the circumstellar disk, thus allowing mass accretion onto the central object. However, the launch mechanism is still being debated. Aims. We would like to exploit high-angular (∼0. 8) resolution and high-sensitivity images to investigate the origin of protostellar jets using typical molecular tracers of shocked regions, such as SiO and SO. Methods. We mapped the inner 22 of the NGC 1333-IRAS2A protostar in SiO(5-4), SO(6 5 -5 4 ), and the continuum emission at 1.4 mm using the IRAM Plateau de Bure Interferometer in the framework of the CALYPSO IRAM large program. Results. For the first time, we disentangle the NGC 1333-IRAS2A Class 0 object into a proto-binary system revealing two protostars (MM1, MM2) separated by ∼560 AU, each of them driving their own jet, while past work considered a single protostar with a quadrupolar outflow. We reveal (i) a clumpy, fast (up to |V − V LSR | ≥ 50 km s −1 ), and blueshifted jet emerging from the brightest MM1 source; and (ii) a slower redshifted jet, driven by MM2. Silicon monoxide emission is a powerful tracer of high-excitation (T kin ≥ 100 K; n H 2 ≥ 10 5 cm −3 ) jets close to the launching region. At the highest velocities, SO appears to mimic SiO tracing the jets, whereas at velocities close to the systemic one, SO is dominated by extended emission, tracing the cavity opened by the jet. Conclusions. Both jets are intrinsically monopolar, and intermittent in time. The dynamical time of the SiO clumps is ≤30-90 yr, indicating that one-sided ejections from protostars can take place on these timescales.

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Rotational excitation of SiO by collisions with helium

Cited by 75 publications

References 52 publications

Revisiting the shocks in BHR71: new observational constraints and H₂O predictions forHerschel

Revisiting the shocks in BHR71: new observational constraints and H₂O predictions forHerschel

A line-confusion limited millimeter survey of Orion KL

First results from the CALYPSO IRAM-PdBI survey

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Rotational excitation of SiO by collisions with helium

Cited by 75 publications

References 52 publications

Revisiting the shocks in BHR71: new observational constraints and H2O predictions forHerschel

Revisiting the shocks in BHR71: new observational constraints and H2O predictions forHerschel

A line-confusion limited millimeter survey of Orion KL

First results from the CALYPSO IRAM-PdBI survey

Contact Info

Product

Resources

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Revisiting the shocks in BHR71: new observational constraints and H₂O predictions forHerschel

Revisiting the shocks in BHR71: new observational constraints and H₂O predictions forHerschel