HST/COS observations of a new population of associated QSO absorbers
  (Abridged) We present a sample of new population of associated absorbers,
detected through Ne VIII \lambda\lambda 770,780 absorption, in HST/COS spectra
of intermediate redshift (0.45 < z < 1.21) quasars (QSOs). Our sample comprised
of total 12 associated Ne VIII systems detected towards 8 lines of sight (none
of them are radio bright). The incidence rate of these absorbers is found to be
40%. Majority of the Ne VIII systems at small ejection velocities (v_ej) show
complete coverage of the background source, but systems with higher v_ej show
lower covering fractions (i.e. f_c < 0.8) and systematically higher values of
N(Ne VIII). We detect Mg X \lambda\lambda 609,624 absorption in 7 out of the 8
Ne VIII systems where the expected wavelength range is cover by our spectra and
is free of any strong blending. We report the detections of Na IX
\lambda\lambda 681,694 absorption, for the first time, in three highest
ejection velocity (e.g. v_ej > 7,000 km/s) systems in our sample. All these
systems show very high N(Ne VIII) (i.e. > 10^{15.6} cm^{-2}), high ionization
parameter (i.e. log U > 0.5), high metallicity (i.e. Z > Z_{\odot}), and
ionization potential dependent f_c values. The observed column density ratios
of different ions are reproduced by multiphase photoionization (PI) and/or
collisional ionization (CI) equilibrium models. While solar abundance ratios
are adequate in CIE, enhancement of Na relative to Mg is required in PI models
to explain our observations.
