4.1.9. Dabs: dust absorption model

This model allows the user to make a zeroth order approximation to the effects of dust on an X-ray absorption spectrum. Basically, compared to absorption by atomic gas, the effects of dust are two-fold:

• Modifications to the fine structure near the edge

• Reduced opacity due to self-shielding in grains

The dabs model only accounts for the second effect, reduced opacity due to self-shielding. The formalism of Wilms et al. (2000) is followed, and we refer to that paper for a full explanation.

In the set of abundances, we use the depletion factors of Wilms et al. (2000).

H	He	Li	Be	B	C	N	O	F	Ne	Na	Mg	Al	Si	P
0	0	1	0	0	0.5	0	0.4	0	0	0.75	0.8	0.98	0.9	0.4
S	Cl	Ar	K	Ca	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn
0.4	0.5	0	0	0.997	0	0.998	0	0.97	0.93	0.7	0.95	0.96	0	0

The numbers represent the fraction of the atoms that are bound in dust grains. Noble gases like Ne and Ar are chemically inert hence are generally not bound in dust grains, but other elements like Ca exist predominantly in dust grains.

Warning

For a realistic model, it is advised to combine the dabs model with a hot model, where (for Solar abundances), the hot model should contain the elements not bound in the dust.

Note

Finally, we note that the amol model can deal with the modified structure near the oxygen edge, but that model does not take self-shielding into account.

The parameters of the model are:

nh : Nominal hydrogen column density in . Default value: .

amin : Minimum grain size in m. Default value: 0.025.

amax : Minimum grain size in m. Default value: 0.25.

p : Power index grain size distribution. Default value: 3.5.

rho : Mean density of the grains in units of 1000 kg . Default value: 3.

ref : Reference atom. Default value: 3 (Lithium). because dust, according to the depletion factors used, does not contain hydrogen, we substitute here formally Lithium. The user is advisednot to change this.

01...30 : Abundances of H to Zn. See the remark on depletion factors above.

The following parameters are common to all our absorption models:

fcov : The covering factor of the absorber. Default value: 1 (full covering)

zv : Average systematic velocity of the absorber (using relativistic Doppler shift)

Recommended citation: Wilms et al. (2000) and Kaastra et al. (2009).