THE ONSET OF WOLF-RAYET WIND OUTFLOW AND THE NATURE OF THE HOT COMPONENT IN THE SYMBIOTIC NOVA PU VULPECULA

We have analyzed temporal variations in the far ultraviolet He II (164 0), Si IV (1393, 1402), and C IV (1548, 1550) line profiles in eight h igh dispersion, International Ultraviolet Explorer Short Wavelength Pr ime spectra of the symbiotic nova PU Vul by comparatively examining th ese profiles on a common velocity scale. We see clear evidence of the onset of a Wolf-Rayet-like wind outflow from the bloated, contracting white dwarf hot component with terminal velocity of almost-equal-to - 550 to - 600 km/s. We have quantitatively analyzed the complicated He II (1640) emission region for the first time and show that the discret e absorption features seen in the He II region occur at precisely the same velocities in each spectrum, thus demonstrating that the absorbin g source is steady and not affected by any orbital motion. We demonstr ate that there is an underlying He II wind emission feature whose true shape is hidden by superposed absorption due to the foreground red gi ant wind flowing in front of the white dwarf and obscuring the white d warf's wind outflow. We present synthetic spectra of He II emission be hind an absorbing slab with v = 20 km/s, T = 5000 K, and column densit ies in the range N = 1 X 10(22) and 1 X 10(23)/cm2 which explain these absorptions. Our analysis of the Si IV and C IV resonance doublets, i n velocity space, reveal temporal variations in the profile between 19 87 and 1991 with the emergence of clear P Cygni profiles in Si IV by 1 990. A nebular emission feature in C III] 1909 also appears in the mos t recent spectra (e.g., SW42538H) while it was absent or extremely wea k in the earliest spectra (e.g., SW36332H), thus strengthening evidenc e that the nebular emission, as seen in permitted and semiforbidden li nes, intensifies in step with the onset of the hot, fast, wind outflow . We also report the first detection of narrow interstellar (circumbin ary shell?) absorption lines near - 1 km/s, most strongly in Al III (1 854, 1862) and Si iv (1392, 1402). We have carried out a rough quantit ative analysis of the He II wind emission by using the theoretical He II Wolf-Rayet profiles of Hamann & Schmutz [A&A, 174, 173 (1987)]. We obtain a lower limit to the He II net emission equivalent width of app roximately 1 angstrom, a hot component temperature in the range 25 000 to 35 000 K, a hot component radius in the range 5R. to 30R., a maxim um wind velocity of almost-equal-to - 600 km/s and a rough upper limit to the mass-loss rate of < 1 X 10(-5) M./yr. To our knowledge, this i s the first quantitative wind analysis, albeit crude, to be carried ou t for the hot component of a symbiotic nova or symbiotic variable.