Engineering topics

Long, Knox S.

Publications and source records attributed to Long, Knox S..

39 records · Page 3

NASA NTRS1991

Far-ultraviolet mapping of the Cygnus Loop with the Voyager 2 Ultraviolet Spectrometer

FUV maps of the Cygnus Loop made using spectroscopic data from the Voyager 2 Ultraviolet Spectrometer are presented. Emission line features at about 980 and about 1035 A dominate the 500-1700 A spectra of the Cygnus Loop as observed with Voyager. Maps were generated in the light of these two features. The 980 and 1035 A maps are compared with X-ray and optical images of the Cygnus Loop that have been sampled in the same manner. From this comparison it is clear that the 980 A feature arises mainly from regions of bright optical emission, whereas the 1035 A emission more closely resembles the X-ray emission. This general impression can be confirmed by inspection of the spectra as a function of position. Spectra extracted from positions corresponding to the primary shock front show the 1035 A feature to be relatively strong, while the 980 A feature is brighter when substantial optical emission is present within the aperture.

Blair, William P.↗

NASA NTRS1991

Supernova remnant evolution in an interstellar medium with evaporating clouds

A new similarity solution that describes the evolution of an SNR expanding into a cloudy interstellar medium is expounded. The solution incorporates a reasonable model of the conductive evaporation of cold clouds embedded in the hot gas behind the shock. The model has two new parameters in addition to those describing the usual Sedov solution for a uniform interstellar medium. The X-ray, infrared, and optical luminosities of remnants with evaporating clouds are calculated, and some of the expected spectral characteristics in the various wavebands are discussed. The effects described may explain the class of remnants observed to have centrally peaked X-ray emission and shell-like radio emission. The total H-alpha luminosity from evaporating clouds predicted by this model is less than that observed for SNRs with centrally peaked thermal X-ray emission. A detailed calculation of the X-ray and optical line emission from evaporating clouds would be very useful in testing this model against the observations.

White, Richard L.↗

NASA NTRS1991

W28 and 3C 400.2 - Two shell-like radio supernova remnants with centrally peaked X-ray morphologies

The paper describes X-ray and optical observations with the Einstein Observatory of two SNRs which are examples of a group of SNRs that have centrally peaked X-ray surface brightness distributions and limb-brightened radio morphologies. X-ray and optical spectra confirm that they are located along lines of sight with substantial intervening absorption, as is the case of other objects that have these morphological characteristics. The hydrogen column density along the line of sight to both remnants is established at (7-11) x 10 to the 21st/sq cm. A thermal origin is proposed as the most likely explanation for the X-ray morphology. It is demonstrated that these SNRs do not have a density and temperature distribution which resembles that of a point explosion in a uniform-density medium, even when the overburden of absorption is considered.

Long, Knox S.↗