4.1.18. Euve: EUVE absorption model

This model calculates the transmission of gas with cosmic abundances as published first by Rumph et al. (1994). It is a widely used model for the transmission at wavelenghts covered by the EUVE satellite ( Å). As it these wavelengths metals are relatively unimportant, it only takes into account hydrogen and helium, but for these elements it takes into account resonances. However it is not recommended to use the model for harder X-rays, due to the neglect of metals such as oxygen etc.

Otherwise the user is advised to use the absm model (Absm: Morrison & McCammon absorption model) or the hot model (Hot: collisional ionisation equilibrium absorption 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 . Default value: (corresponding to , a typical value at low Galactic latitudes).

he1:

The He  / H  ratio. Default value: 0.1.

he2:

The He  / H  ratio. Default value: 0.01.

icov:

Type of the covering fraction. Default value: 2 (constant, set by fcov). If icov=1, full covering is applied. If icov=3, covering fraction follows a tangent function that increases with energy. If icov=4, covering fraction follows an inverse tangent function that decreases with energy. See description in pion.

fcov:

The covering factor of the absorber if icov=2. Default value: 1 (full covering). If icov=3 or 4, it sets the covering factor at the high energy end.

lcov:

The covering factor of the absorber at the low energy end. Default value: 1. lcov is applied only when icov=3 or 4. See description in pion.

ecov:

The energy when the covering factor changes from lcov to fcov. Only applied if icov=3 or 4.

acov:

The width of the transit on covering factor. Only applied if icov=3 or 4.

Recommended citation: Rumph et al. (1994).