On the discrepancy between the X-ray and UV absorption measurements of
  OVI in the local ISM
  The total amount of OVI present in the interstellar medium (ISM) obtained via
absorption measurements in UV and X-ray spectra is currently in disagreement,
with the latter being significantly larger (by a factor of 10 or more) than the
former. Previous works have proposed that the blend of the OVI Ka line (22.032
A) with the OII Kb-L12 line (22.04 A) could account for the stronger absorption
observed in the X-ray spectra. Here we present a detailed study of the oxygen
absorption in the local ISM, implementing our new model IGMabs, which includes
photoabsorption cross-sections of highly ionized species of abundant elements
as well as turbulence broadening. By analyzing high-resolution Chandra spectra
of 13 low mass X-ray binaries (LMXBs) and 29 extragalactic sources, we have
estimated the column densities of OI-OIII and from OVI-OVIII along multiple
line-of-sights. We find that in most cases the OII Kb-L12 line accounts for <
30% of the total OVI Ka + OII Kb. We conclude that the amount of OII predicted
by our model is still insufficient to explain the discrepancy between X-ray and
UV measurements of OVI column densities.
