X-ray spectra of the Puppis A and the VELA supernova remnants

Low-energy X-ray spectra are presented for (i) the entire Vela supernova remnant (SNR), (ii) the two most intense subregions of the Vela SNR, and (iii) the Puppis A SNR. Acceptable /subx//sup 2/ fits are obtained from the model of a high-temperature, low-density plasma with Allen cosmic abundances when thermal bremsstrahlung, radiative recombination, line emission, and interstellar absorption are included. An increase of 45-fold in the Si abundance as suggested by Burginyon, Hill, and Seward for the entire Vela SNR is found unacceptable by chi/sup 2/ tests of our spectra. The two enhanced regions of Vela are found to have different temperatures. A deficiency of at least a factor of 3 is seen in the O vii and O viii emission from the entire Vela SNR. Because ultraviolet observations (Burton, Evans, and Griffin; Jenkins and Meloy) indicate a normal abundance of oxygen, this is interpreted as evidence for the existence of nonequilibrium conditions in the emitting plasma. (AIP)