High-velocity winds in close binaries with accretion disks. II - The view along the plane of the disk

Abstract

We present phase-resolved, ultraviolet spectra of the eclipsing cataclysmic binaries RW Trianguli and DQ Herculis. Both stars display N v /1240, Si iv 21400, C iv 21549, and He n 21640 in emission. The strongest spectral feature in both stars is C iv 21549. In RW Tri this line has an equivalent width of 40 Â (out of eclipse), a FWHM of 13 Â, and is asymmetric with the peak displaced redward of the line centroid by 4 Â; the blue wing of the line extends to velocities of —3000 km s“1. The C iv line in DQ Her has an equivalent width of 110 Â (out of eclipse), and a FWHM of 9.5 Â; the out-of-eclipse line profile rs not obviously asym- metric, but the eclipse profile is skewed redward of line center. In both stars there is a deep eclipse of the UV continuum, representing an occultation of the interior regions of an accretion disk surrounding the degenerate dwarf. None of the spectral lines in either binary system are eclipsed to the same degree as the UV continuum, indicating that the lines are formed in an extended region above and below the disk. The distinctive morphol- ogy of RW Tri’s lines suggests an origin in an accelerating wind. The observed hard X-ray flux from RW Tri is not sufficient to drive the wind, but UV and/or EUV radiation from the inner disk could provide the required energy. The continuum spectrum of RW Tri is significantly reddened, with £(£—F) = 0.25; this result when combined with previous measurements of the surface brightness distribution of RW Tri’s disk yields a mass accretion rate of about 1018 g s-1