Abstract
We have used multiple mid-infrared observations at 4.5 μm obtained with the infrared array camera, of the compact young stellar bipolar outflow Cep E to measure the proper motion of its brightest condensations. The images span a period of yr and have been reprocessed to achieve a higher angular resolution than their normal beam . We found that for a distance of 730 pc, the tangential velocities of the north and south outflow lobes are and respectively, and moving away from the central source roughly along the major axis of the flow. A simple 3D hydrodynamical simulation of the H2 gas in a precessing outflow supports this idea. Observations and models confirm that the molecular hydrogen gas, traced by the pure rotational transitions, moves at highly supersonic velocities without being dissociated. This suggests either a very efficient mechanism to reform H2 molecules along these shocks or the presence of some other mechanism (e.g. strong magnetic field) that shields the H2 gas.
Highlights
The measurement of proper motions for Herbig–Haro (HH) outflows and stellar jets has a long tradition and has played a fundamental role in our understanding of early phases of evolution of low mass stars, including their accretion rates, mass loss and disk dissipation The original work by Herbig and Jones (1981) on the first and brightest HH objects 1, 2 and 3, using photographic plates over a 34 yr period, set up the framework of the mass loss process in proto-stars and their interaction with the surrounding medium
We have used multiple mid-infrared observations at 4.5 μm obtained with the infrared array camera, of the compact (∼1.4′) young stellar bipolar outflow Cep E to measure the proper motion of its brightest condensations
A 50 km s−1 tangential velocity is certainly consistent with the value of ∼62 km s−1 of the north lobe, that plunges deeper into the cloud, and is a bit smaller than the 94 km s−1 value of the south lobe, where one detects at optical wavelengths HH 377, i.e the observed proper motions seem to reflect the difference in physical environment between the two lobes
Summary
The measurement of proper motions for Herbig–Haro (HH) outflows and stellar jets has a long tradition and has played a fundamental role in our understanding of early phases of evolution of low mass stars, including their accretion rates, mass loss and disk dissipation (see e.g. McKee and Ostriker 2007, Bally 2009) The original work by Herbig and Jones (1981) on the first and brightest HH objects 1, 2 and 3, using photographic plates over a 34 yr period, set up the framework of the mass loss process in proto-stars and their interaction with the surrounding medium. The large proper motions observed in the HH 1/2 system in the atomic ionic gas (Herbig and Jones 1981) have been measured in the NIR as well, using the molecular hydrogen shock excited emission vibrational transition (v = 1 − 0 S(1)) at 2.121 μm (Noriega-Crespo et al 1997). The AWAIC software optimizes the coaddition of individual frames by making use of the point response function as an interpolation kernel, to avoid flux losses in undersampled arrays like those of IRAC, and allows a resolution enhancement (HiRes) of the final image, by removing its effect from the data in the deconvolution process We have used this method quite successfully in the HH 1/2 outflow (Noriega-Crespo and Raga 2012), and as mentioned above, a similar method has been used on Cep E (Velusamy et al 2011) and HH 46/47 (Velusamy et al 2007). In figure 2 we show the five epochs that are being analyzed; the IRAC images are the HiRES AWAIC reprocessed after 60 iterations
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