ELEMENTAL ABUNDANCES OF THE SUPERNOVA REMNANT G292.0- EVIDENCE FOR A MASSIVE PROGENITOR(1.8 )

We present a comprehensive nonequilibrium ionization (NEI) analysis of X-ray spectral data from the Einstein Observatory and EXOSAT for the supernova remnant G292.0+1.8. The spectra are well described by a sing le-temperature, single-timescale NEI model with kT = 1.64(-0.19)(+0.29 ) keV and n(e)= (5.55(-1.12)(+1.20))s, which establishes that this rem nant is indeed young and in the ionizing phase of evolution of its X-r ay spectrum. We determine the abundances of the elements O, Ne, Mg, Si , S, Ar, and Fe and examine their variation over the allowed range of column density, kT, and n(e), t. Numerical calculations of the nucleos ynthesis expected for a 25 M(.) progenitor agree best with the fitted abundances; in fact the minimum rms percent difference between this mo del and the derived abundances is only 15%. From the fitted emission m easure and a simple geometric model of the remnant we estimate the mas s of X-ray-emitting plasma to be 9.3(-6.2)(+11.9) M(.), for an assumed distance of 4.8 +/- 1.6 kpc. Additional errors on this mass estimate, from clumping of the ejecta, for example, may be substantial. No evid ence was found for a difference in the thermodynamic state of the plas ma as a function of elemental composition based on analysis of the ind ividual ionization timescales of the various species. In this sense th en, G292.0+1.8 resembles the remnant Cas A (another product of a massi ve star supernova), while it is different from the remnants of SN 1572 (Tycho) and SN 1006, both of which are believed to be from Type Ia su pernovae.