Modeling the oxygen K absorption in the interstellar medium: an {\it
  XMM}-Newton view of Sco X-1
  We investigate the absorption structure of the oxygen in the interstellar
medium by analyzing {\it XMM}-Newton observations of the low mass X-ray binary
Sco X-1. We use simple models based on the O {\sc i} atomic cross section from
different sources to fit the data and evaluate the impact of the atomic data in
the interpretation of astrophysical observations. We show that relatively small
differences in the atomic calculations can yield spurious results. We also show
that the most complete and accurate set of atomic cross sections successfully
reproduce the observed data in the $21-24.5$ {\AA} wavelength region of the
spectrum. Our fits indicate that the absorption is mainly due to neutral gas
with an ionization parameter of $\xi=10^{-4}$ erg cm s$^{-1}$, and an oxygen
column density of $N_{\mathrm{O}}\approx 8-10\times 10^{17}$ cm$^{-2}$. Our
models are able to reproduce both the K edge and the K$\alpha$ absorption line
from O {\sc i}, which are the two main features in this region. We find no
conclusive evidence for absorption by other than atomic oxygen.
