 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| * |
At soft X-ray
energies, interstellar
|
|
|
|
attenuation is
primarily due to K-shell
|
|
|
photoelectric
absorption by He, C, N,
|
|
|
|
O, and Ne.
|
|
|
| * |
The most
prominent “feature” expected
|
|
|
|
is the neutral O
K-edge at 0.532 keV.
|
|
|
Although this
was included in standard
|
|
|
|
models at the
time, it had never been
|
|
|
explicitly
detected.
|
|
|
| * |
Charles et al.
used the HEAO A-2 LED
|
|
|
|
observations of
the Crab Nebula to
|
|
|
study this
feature. The Kahn & Blissett
|
|
|
|
deconvolution
procedure showed that
|
|
|
the edge was
there. Spectral fits
|
|
|
|
indicated
consistency with the standard
|
|
|
cosmic abundance
of oxygen, given the
|
|
|
|
inferred
hydrogen column to the source.
|