OBSERVATIONS OF THE BRIGHT NOVALIKE VARIABLE IX-VELORUM WITH THE HOPKINS ULTRAVIOLET TELESCOPE

The Hopkins Ultraviolet Telescope, an experiment flown on the Space Shuttle as part of the Astro-1 mission, was used to obtain a spectrum of the novalike variable IX Vel (= CPD -48-degrees 1577) in the wavelength range 830-1860 angstrom. The observation revealed a rich absorption-line and continuum spectrum that peaks near 1050 angstrom at a flux of 1.6 x 10(-11) ergs cm-2 s-1 angstrom-1. In the sub-Lyman-alpha region, some of the more prominent absorption lines are S VI lambdalambda933, 945, C III lambda977, Lyman-beta, O VI lambdalambda1032, 1038, P V lambdalambda1118, 1128, and C III lambda1176. No emission was detected below the Lyman limit. The overall continuum shape of IX Vel in the FUV can be approximated using models of an optically thick accretion disk in which the integrated spectrum has been constructed by summing model stellar atmospheres or proper disk model spectra. However, if the distance to IX Vel is approximately 95 pc, standard disk models without reddening cannot simultaneously reproduce the color and flux in the UV. While interstellar reddening can reconcile this difference, the amount of reddening appears inconsistent with the absence of a 2200 angstrom bump in the spectrum and the very low H I column density measured along the line of sight. Improved fits to the data can be obtained by modifying the accretion disk structure within three white dwarf radii. None of the models reproduces the profiles of the Li- and Na-like ions, which are observed as strong but relatively narrow absorption lines, and which are almost surely due to a wind above the disk.