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A. Riera A. Raga R. López G. Anglada R. Estalella 《Astrophysics and Space Science》1995,224(1-2):551-552
New, deep, wide-field [SII] images of the HL Tauri region show the extended spatial structure of the HH 30 jet and counter-jet. At an angular distance of 300 arcsec toward the NE, the HH 30 jet ends in a group of scattered condensations. This previously undetected structure might correspond to a broken-up working surface. Our images also include HH 262, which is shown to have a previously undetected extended emission region. 相似文献
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A. C. Raga 《Astrophysics and Space Science》1993,208(2):163-189
A considerable amount of effort has been made towards obtaining a theoretical understanding of the collimated, optically detected outflows (Herbig-Haro objects) ejected by young stars. The most clear results have been obtained for the case of the Herbig-Haro jets, a loosely defined category which groups the Herbig-Haro (HH) objects with jet-like structures of aligned knots. In particular, it has recently been shown that at least some of the characteristics of the HH jets can be straightforwardly explained in terms of models of jets from variable sources. This paper presents a review of the properties of models of jet flows from sources with a variability in the ejection velocity, in the ejection direction, and with a general velocity+direction variability. Also, a comparison between the observational characteristics of HH jets and the predictions from variable source jet models is carried out. 相似文献
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This paper reviews the numerical simulations of radiative jets with concrete predictions of the emitted radiation, which can be compared directly with observations of individual HH objects. The only models that have been developed to this point are the “internal working surface model” (in which the structures along HH jets are interpreted as working surfaces resulting from a time-variability in the ejection) or the “Kelvin-Helmholtz instability model” (in which the HH knots are associated with shocks resulting from K-H instabilities in the jet beam/environment boundary). The predictions of intensity maps, line ratios, line profiles and proper motions are discussed. 相似文献
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High velocity jets from young stars interact with the surrounding molecular environment and molecular outflows quite possibly are the result. This interaction can take place through the formation of a turbulent mixing layer. Models have been constructed (following Cant/'o and Raga) of a plane mixing layer in the boundary between a high velocity, atomic wind (i.e., the stellar jet) and a stationary, molecular environment, computed considering a detailed chemical network.The chemical composition of the mixing layer initially corresponds to the direct mixture of the (atomic) jet and (molecular) environmental material. However, we find that the mixing layer is hot (with temperatures exceeding 104 K), and the surprising only partial dissociation of H2 means that a number of molecules are either created or survive in the high velocity gas. This contrasts with the slower, cooler flows that have tended to be termed a molecular outflow.The emission from such atomic jet/molecular environment mixing layers is dominated by emission in the rotational and vibrational lines of H2. As a result of the high temperatures and velocities (ranging from zero to the jet velocity) of these mixing layers, the predicted H2 emission line spectrum has interesting characteristics. 相似文献
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Jiménez J. C. Raga G. B. Baumgardner D. Castro T. Rosas I. Báez A. Morton O. 《Natural Hazards》2004,31(1):21-37
A 17-day field campaign was carried out in April–May 1999 to determine thecontribution that gaseous volcanic emissions make to the compositionof solid particles,particularly to the presence and quantity of sulfates. Theexperimental site was located inTonantzintla (in the State of Puebla), only 30 km E from the volcanoPopocatépetl, whichhas been in an active phase since the end of 1993. An analysis ofthe carbon monoxide(CO) and sulfur dioxide (SO2) in the ambient air identifiedvolcanic influence in 6 out ofthe 17 days sampled. Particles collected in an 8-stage cascadeimpactor were analyzed for inorganic ions (by liquid chromatography).A non-parametric test indicates asignificant difference on the total particle mass and thesulfate fraction between days withand without volcanic influence. This difference was predominantlyobserved in the stages that collect the smaller particles. Windsat 500 mb (roughly corresponding to thesummit of the volcano) indicate a westerly transport from thevolcano to the experimentalsite, even though surface winds do not show a clear signal ofsuch a transport. Back trajectories from the experimental site werecalculated and clearly indicated that air parcels on the daysindependently identified as with volcanic influence had indeed passed over the volcano. 相似文献
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A. C. Raga J. Cantó S. Curiel & S. Taylor 《Monthly notices of the Royal Astronomical Society》1998,295(4):738-742
It has been pointed out in the past that it is impossible to accelerate molecular material to velocities ≥ 25 km s−1 with gasdynamic shocks without dissociating the gas. Because of this, it has been argued that observations of molecular emission with radial velocities ∼ 20–100 km s−1 imply the presence of 'C-shocks' (which have much lower post-shock temperatures, and therefore do not dissociate the gas) and the existence of strong (∼ 10–100 μG) magnetic fields. In this paper, we discuss an alternative mechanism for accelerating molecular material to high velocities: a high-velocity, low-density wind drives a non-dissociative shock (with shock velocity v cs ≤ 25 km s−1 ) into a high-density, molecular clump. Once this shock wave has gone through the clump, the molecular material is moving at a velocity ∼ v cs and has a gas pressure approximately equal to the ram pressure of the impinging wind. The compressed molecular clump can now be accelerated directly by the ram pressure of the wind (without the passage of further shocks through the molecular material), and will eventually move at the wind velocity. This mechanism has been previously invoked to explain high-velocity molecular emission. However, numerical simulations have shown that a wind/clump interaction leads to the fragmentation of the clump before it can be accelerated to large velocities. In our numerical simulation (which includes an approximate treatment of the relevant microphysics) we find that the fragments that are produced are still largely molecular, and that they are rapidly accelerated to velocities comparable to the wind velocity. We therefore conclude that a wind/molecular clump interaction is indeed a valid mechanism for producing high-velocity molecular features. 相似文献
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