Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...447..742l&link_type=abstract
Astrophysical Journal v.447, p.742
Astronomy and Astrophysics
Astronomy
19
Ism: Jets And Outflows, Radio Lines: Ism, Stars: Circumstellar Matter, Stars: Mass Loss, Stars: Pre-Main-Sequence
Scientific paper
Assuming that molecular outflows from young low-mass stars are driven by fast neutral atomic winds, we further explore the possibility that these winds interact with the ambient cloud through entrainment of molecular material. This paper is aimed to determine the energy balance and the resulting thermal structure of the entrainment region.
We model the entrainment region as a mixing layer along the walls of a cavity within the cloud itself. We make use of the 21 cm H I spectral profiles observed in L1551 to specify a priori the overall geometry of the flow and the amount of entrainment at each point Assuming momentum conservation in the layer, we determine in a single parcel approximation the radial temperature profile of the mixing layer.
We find that, with a reasonable choice of assumptions, the temperature in these regions is between 3000 and 5000 K. This results from heating due to the dissipation of wind kinetic energy as it decelerates outward due to mass entrainment, and from cooling by rovibrational emission of molecular hydrogen. We find that, because of the low density, short crossing time, and replenishment from the cloud, the H2 is not dissociated and acts as the main coolant in the layer. Even taking into account nonthermal impacts, due to the low density, the thermal coupling between gas and dust is low and results in much lower dust temperatures (10-20 K) through most of the mixing layer. For the same reason dust is not an effective coolant. In the case of L1551 the H2 emission from the mixing layer, e.g., in the υ = 1-0 S(1) line, should be spread over most of the CO lobes and within the detection limits of current (arcminute resolution) near-infrared spectrographs.
Giovanardi Carlo
Lizano Susana
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