We present far-ultraviolet spectroscopy of the cores of the massive cooling flow clusters Abell 1795 and 2597 obtained with FUSE. As the intracluster gas cools through 3 x 10(exp 5)K, it should emit strongly in the O VI lambda(lambda)1032,1038 resonance lines. We report the detection of O VI (lambda)1032 emission in A2597, with a line flux of 1.35 +/- 0.35 x 10(exp -15) erg/sq cm s, as well as detection of emission from C III (lambda)977. A marginal detection of C III (lambda)977 emission is also reported for A1795. These observations provide evidence for a direct link between the hot (10(exp 7) K) cooling flow gas and the cool (10(exp 4) K) gas in the optical emission line filaments. Assuming simple cooling flow models, the O VI line flux in A2597 corresponds to a mass deposition rate of approx. 40 solar mass /yr within the central 36 kpc. Emission from O VI (lambda)1032 was not detected in A1795, with an upper limit of 1.5 x 10(exp -15) erg/sq cm s, corresponding to a limit on the mass cooling flow rate of M(28 kpc) less than 28M solar mass/ yr. We have considered several explanations for the lack of detection of O VI emission in A1795 and the weaker than expected flux in A2597, including extinction by dust in the outer cluster, and quenching of thermal conduction by magnetic fields. We conclude that a turbulent mixing model, with some dust extinction, could explain our O VI results while also accounting for the puzzling lack of emission by Fe(sub XVII) in cluster cooling flows.

Oegerle, W. R.↗

NASA NTRS1981

The Gemini-Monoceros X-ray enhancement - A giant X-ray ring

A 1.5 deg spatial resolution map of the 1/4 KeV diffuse X-ray background enhancement in the Gemini and Monoceros constellations is found to show a circular ring-shaped emission feature with a diameter of 20 deg. The feature and possible X-ray contributions from the Mon OB1 association and neighboring supernova remnants are discussed. From 300 pc, the region has a radius of 50 pc, with an emitting electron density of 0.01 per cu cm. A shell of expanding neutral hydrogen and nonthermal radio spur is observed outside the ring with the X-ray emitting pulsar PSR 0656 + 14 lying close to the center of the ring. Origins of the ring are discussed, ruling out formation by the association Mon OB1. The ring is considered to be a field supernova remnant formed by the progenitor of the central pulsar, and providing constraints on theories of remnant evolution. This conclusion is found to agree with estimated supernova rates, and the absence of additional examples of this stage of evolution is an observational selection effect.

Nousek, J. A.↗