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Session 74 - Supernova Remnants.
Display session, Thursday, June 13
Great Hall,
The Vela supernova remnant is one of the most nearby and least reddened galactic supernova remnants. As such, it is one of the best laboratories for studying interstellar blast waves and their interaction with the interstellar medium. We have used the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 space shuttle mission in 1995 March to observe the 900 - 1850 Å\ spectrum of several locations within the extended filamentary shell. Two positions, on the eastern limb of the remnant, correspond to one of the regions identified by Aschenbach et al. (1995, Nature, 373, 587) as a possible ``bullet'' of SN ejecta. Our spectra show this region to be simply a ``breakout'' in the SNR shell, consisting of normal abundance, recently-shocked interstellar gas. The observed positions, which have nearly identical UV spectra, have very different optical spectra, which we attribute to shock ``completeness'' differences between the two positions.
A second pair of pointings in a region projected near the center of the remnant have been used to study the effects of resonance line scattering, which may affect many SNR observations done with (for instance) IUE over the years. This has been accomplished by observing a low surface brightness face-on shock and comparing against the spectrum of a nearby edge-on filament that arises from the same (or similar) section of the blast wave. Comparison against shock models allows us to quantify these resonant scattering effects. We find as a general result that this effect may have caused substantial and systematic underestimates of shock velocities as estimated from previous UV observations.
Support for this work was provided by NASA contract NAS5-27000 to the Johns Hopkins University and NASA Grant NAG8-1074 to the Smithsonian Astrophysical Observatory.
