Other
Scientific paper
Jul 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006hst..prop10807s&link_type=abstract
HST Proposal ID #10807. Cycle 15
Other
Scientific paper
Previous WFPC2 observations have led to the serendipitous discovery of an extended, highly-collimated, ``pulsed" bipolar jet emanating from a compact planetary nebula, He 2-90. Subsequently, an average proper motion of the knots in the jet was measured, which together with radial velocities, enabled us to characterise the basic physical properties of the jet. The knotty jet in He 2-90 resembles other prominent examples of pulsed jets in young stellar objects or symbiotic stars, but is probably by far the best example yet of a non-relativistic, symmetric, jet in a ``clean" astrophysical environment. The formation acceleration and collimation of jets is not fully understood, specially in the case of jets in dying stars. We now propose to re-image He 2-90 with WFPC2 and exploit the factor 3.5 longer time baseline now available from the first-epoch observations in September 1999, in order to measure the proper motion of individual knots in the jet with unprecedented accuracy. These data will enable us to characterise the ejection history of the source, specially deviations from a constant period latter is related to the binary period of the system, e.g., due to instabilities in the accretion mechanism. We will also be able to test if the ejection mechanism is symmetric: any deviation in the ejection history of the knots in the opposing jet beams, will indicate a magnetic field structure and/or the accretion disk which is not symmetric across the equatorial plane. We will also carry out deep imaging with the ACS/WFC camera in order to determine the shapes/sizes of a large number of knots. The shapes/sizes of the knots, and changes with distance from the source probe the strength of the magnetic field inside the jet. HRC imaging of the central source and jet on sub-arcsecond scales will be carried out to probe the magnetic field close to the jet source, and deviations from linearity in the jet-beam which may result from instabilities in the magnetic field. These data will allow us to significantly improve our existing 2-dimensional MHD model of the He2-90 jet, and/or provide impetus for new 3-dimensional models.
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