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Session 18 - The Interstellar Medium.
Oral session, Monday, June 08
Padre,
The [O III] \lambda5007Å\ skin observed around the crab nebula is best explained as a region of cooling behind a radiative shock driven by synchrotron pressure, and sweeping up freely expanding ejecta of the supernova (Sankrit amp;\ Hester 1997). Shock models predict elevated [Ne V] \lambda3426Å\ emission if the shock velocity is greater than 170 km/s. Ratios of [Ne V] to [O III] emission can be used to trace the velocity profile of the shock (Sankrit amp;\ Hester 1997). We present narrowband [Ne V] and [O III] images of the crab nebula as part of a study to measure the properties of the shock. These line filter images were taken early this year at the Steward 90 inch telescope on Kitt Peak. One set of images includes the location where Davidson observed high [Ne V] emission (Davidson 1979). While the [O III] image at this position shows the skin, filaments, and complex structure seen previously (Sankrit amp;\ Hester 1997), the [Ne V] emission forms a prominant smooth skin at the outer edge of the [O III] skin, with additional [Ne V] emission lining the stronger [O III] filaments. These observations support the existence of a shock and by extension support the existence of expanding ejecta from the supernova beyond the visible remnant.
