BROAD NE-VIII LAMBDA-774 EMISSION FROM QUASARS IN THE HST-FOS SNAPSHOT SURVEY (ABSNAP)

We discuss the strength and frequency of broad Ne VIII lambda 774 emission from quasars measured in the HST-FOS snapshot survey (Absnap). Five sources in the survey have suitable redshifts (0.86 less than or equal to z(em) less than or equal to 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five sources have a strong broad emission line near 774 Angstrom (rest), and the remaining two sources have a less securely measured line near this wavelength. We identify these lines with Ne VIII lambda 774 based on the measured wavelengths and theoretical estimates of various line fluxes (Hamann et al. 1995a). Secure Ne VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne VIII lambda 774 emission is common in quasars, with typical strengths between similar to 25% and similar to 200% of O VI lambda 1034. These Ne VII lambda 774 measurements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They also suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (>15.2 ryd, lambda < 60 Angstrom). Photoionization calculations using standard incident spectra indicate that the Ne vm emission requires ionization parameters U greater than or similar to 5, total column densities N-H greater than or similar to 10(22) cm(-2) and covering factors greater than or similar to 25%. The temperatures could be as high as similar to 10(5) K. If the gas is instead collisionally ionized, strong Ne vm would imply equilibrium temperatures in the range similar to 400,000 less than or similar to T-e less than or similar to 10(6) K. In either case, the highly ionized Ne VIII emission regions would appear as X-ray ''warm absorbers'' if they lie along our line of sight to the X-ray continuum source.