Determining the Lifetime of Planetary Nebula Knots from Observations of the Core of the Helix Nebula.

Details Determining the Lifetime of Planetary Nebula Knots from Observations of the Core of the Helix Nebula. Determining the Lifetime of Planetary Nebula Knots from Observations of the Core of the Helix Nebula.

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005hst..prop10628o&link_type=abstract

HST Proposal ID #10628

Computer Science

Hst Proposal Id #10628 Interstellar And Intergalactic Medium

Scientific paper

Knots within the Planetary Nebulae {PN} are ubiquitous components and form at the interface of the expanding ionized zone and the surrounding dusty and molecule-rich neutral layers. About half of the total mass ejected by the precursor star becomes trappped in the Knots, which will join the Interstellar Medium {ISM} within a few tens of thousands of years. If they survive, they may be the source of the micro-structures that appear to be common in the ISM, a result that would be important in understanding the exchange of matter between stars and the ISM. We propose observations that will characterize the Knots over a wider ionization range and ages than has been done before, which should yield the best model for the Knots and therefore the best prediction of their fates. Knots are not seen within a well defined distance from the central star. We don't know if this is because they are being destroyed by photoevaporation {since the inner Knots would be the youngest}, an important factor in our modeling. However, the inner core of the Helix Nebula has not been imaged in the HeII emission that dominates the region. We propose eight orbits of observations that will search the inner core of the Helix for undetected knots using the WFPC2 HeII F469N filter and the ACS-WFC F502N filter that isolates [OIII] emission. Our WFPC2 pointing will also allow imaging the best studied knot in HeII, giving us the best possible data for that Knot. These combined results will be modeled with the new Hydro-Cloudy code, allowing us to determine if they will survive the PN stage and become components of the ISM. At no additional cost of observing time we will be able to derive a calibration of the WFPC2 F469N filter, to make unprecedented quality parallel images in molecular hydrogen, and to extended the coverage of high resolution emission-line images of the Helix Nebula.

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