2001ApJ...560..187O

We present far-ultraviolet spectroscopy of the cores of the massive cooling-flow clusters Abell 1795 and 2597, obtained with the Far Ultraviolet Spectroscopic Explorer. As the intracluster gas cools through 3x10⁵ K, it should emit strongly in the O VI λλ1032, 1038 resonance lines. We report the detection of O VI λ1032 emission in A2597, with a line flux of 1.35±0.35x10^–15 ergs.cm^–2.s^–1, as well as detection of emission from C III λ977. A marginal detection of C III λ977 emission is also reported for A1795. These observations provide evidence for a direct link between the hot (10⁷ K) cooling-flow gas and the cool (10⁴ 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 ∼40 M_☉ yr^–1 within the central 36 kpc. Emission from O VI λ1032 was not detected in A1795, with an upper limit of 1.5x10^–15 ergs.cm^–2.s^–1, corresponding to a limit on the mass cooling-flow rate of M{dot}(28 kpc)<28 M_☉ yr^–1. 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 XVII in cluster cooling flows.