4.1.1. Absm: Morrison & McCammon absorption modelΒΆ

This model calculates the transmission of neutral gas with cosmic abundances as published first by Morrison & McCammon (1983). It is a widely used model. The following is useful to know when this model is applied:

  1. The location of the absorption edges is not always fully correct; this can be seen with high resolution grating spectra

  2. The model fails in the optical/UV band (i.e., it does not become transparent in the optical)

  3. No absorption lines are taken into account

  4. The abundances cannot be adjusted

If all the above is of no concern (as is the case in many situations), then the Morrison & McCammon model is very useful. In case higher precision or more detail is needed, the user is advised to use the Hot: collisional ionisation equilibrium absorption model model with low temperature in SPEX, which gives the transmission of a slab in collisional ionisation equilibrium.

The parameters of the model are:

nh : Hydrogen column density in 10^{28} \mathrm{m}^{-2}. Default value: 10^{-4} (corresponding to 10^{24} \mathrm{m}^{-2}, a typical value at low Galactic latitudes).
f : The covering factor of the absorber. Default value: 1 (full covering)

Recommended citation: Morrison & McCammon (1983).