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Post Info TOPIC: VLA 1623
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Title: H2O line mapping at high spatial and spectral resolution - Herschel observations of the VLA1623 outflow
Authors: P. Bjerkeli, R. Liseau, B. Larsson, G. Rydbeck, B. Nisini, M. Tafalla, S. Antoniucci, M. Benedettini, P. Bergman, S. Cabrit, T. Giannini, G. Melnick, D. Neufeld, G. Santangelo, E. F. van Dishoeck

Apart from being an important coolant, H2O is known to be a tracer of high-velocity molecular gas. Recent models predict relatively high abundances behind interstellar shockwaves. The dynamical and physical conditions of the H2O emitting gas, however, are not fully understood yet. We aim to determine the abundance and distribution of H2O, its kinematics and the physical conditions of the gas responsible for the H2O emission. The observed line profile shapes help us understand the dynamics in molecular outflows. We mapped the VLA1623 outflow, in the ground-state transitions of o-H2O, with the HIFI and PACS instruments. We also present observations of higher energy transitions of o-H2O and p-H2O obtained with HIFI and PACS towards selected outflow positions. From comparison with non-LTE radiative transfer calculations, we estimate the physical parameters of the water emitting regions. The observed water emission line profiles vary over the mapped area. Spectral features and components, tracing gas in different excitation conditions, allow us to constrain the density and temperature of the gas. The H2O emission originates in a region where temperatures are comparable to that of the warm H2 gas (T\gtrsim200K). Thus, the H2O emission traces a gas component significantly warmer than the gas responsible for the low-J CO emission. The H2O column densities at the CO peak positions are low, i.e. N(H2O) \simeq (0.03-10)x10e14 cm-2. The H2O abundance with respect to H2 in the extended outflow is estimated at X(H2O)<1x10e-6, significantly lower than what would be expected from most recent shock models. The H2O emission traces a gas component moving at relatively high velocity compared to the low-J CO emitting gas. However, other dynamical quantities such as the momentum rate, energy and mechanical luminosity are estimated to be the same, independent of the molecular tracer used, CO or H2O.

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Blobrana


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Title: Sub-arcsecond SMA observations of the prototype Class 0 object VLA1623 at 1.3 mm: A single protostar with a structured outflow cavity ?
Authors: A. J. Maury, N. Ohashi. Ph. Andre

We present 1.3-mm sub-arcsecond SMA observations of the prototypical Class 0 protostar VLA1623. We report the detection of 1.3-mm continuum emission both from the central protostellar component VLA1623 and two additional sources, Knot-A and Knot-B, already detected at longer wavelengths. Knot-A and Knot-B are both located along the western cavity wall opened by the protostellar outflow from VLA1623. Our SMA observations moreover show that these two continuum sources are associated with bright, high- velocity 12CO(2-1) emission, slightly shifted downstream the outflow propagation direction with respect to the 1.3-mm continuum emission peaks. The alignment of Knot-A and Knot-B along the protostellar outflow cavity, as well as the compactness of their 1.3- mm continuum emission and the properties of the associated CO emission suggest that these two sources are tracing outflow features due to shocks along the cavity wall, rather than protostellar objects. While it was considered as one of the best example of close protobinary system so far, the present analysis suggests that the prototypical Class 0, VLA1623, is single at scales a > 100 AU probed by our SMA observations. Moreover, we present here the second robust case of compact millimetre continuum emission produced by interactions between the protostellar jet and the envelope of a Class 0 protostar, which suggests a high occurrence of these outflow features during the embedded phase.

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