3.1.7. Comp: create, delete and relate spectral components Overview

In fitting or evaluating a spectrum, one needs to build up a model made out of at least 1 component. This set of commands can create a new component in the model, as well as delete any component. Usually we distinguish two types of spectral components in SPEX.

The additive components correspond to emission components, such as a power law, a Gaussian emission line, a collisional ionization equilibrium (CIE) component, etc.

The second class (dubbed here multiplicative components for ease) consists of operations to be applied to the additive components. Examples are truly multiplicative operations, such as the Galactic absorption, where the model spectrum of any additive component should be multiplied by the transmission of the absorbing interstellar medium, warm absorbers etc. Other operations contained in this class are redshifts, convolutions with certain velocity profiles, etc.

The user needs to define in SPEX which multiplicative component should be applied to which additive components, and in which order. The order is important as operations are not always communative. This setting is also done with this component command.

If multiple sectors are present in the spectral model or response matrix (see Section Sectors and regions) then one has to specify the spectral components and their relation for each sector. The possible components to the model are listed and described in Section Spectral models.

Note that the order that you define the components is not important. However, for each sector, the components are numbered starting from 1, and these numbers should be used when relating the multiplicative components to the additive components.

If you want to see the model components and the way they are related, type “model show”.


If in any of the commands as listed above you omit the sector number or sector number range, the operation will be done for all sectors that are present. For example, having 3 sectors, the “comp pow” command will define a power law component for each of the three sectors. If you only want to define/delete/relate the component for one sector, you should specify the sector number(s). In the very common case that you have only one sector you can always omit the sector numbers.


After deleting a component, all components are re-numbered! So if you have components 1,2,3 for example as pow, cie, gaus, and you type “comp del 2”, you are left with 1=pow, 2=gaus. Syntax

The following syntax rules apply:

comp [#i:] #a : Creates a component #a as part of the model for the (optional) sector range #i:
comp delete [#i1:] #i2: : Deletes the components with number from range #i2: for sector range (optional) #i1. See also the warning above
comp relation [#i1:] #i2: #i3,...,#in : Apply multiplicative components #i3, …, #in (numbers) in this order, to the additive components given in the range #i2: of sectors in the range #i1 (optional). Note that the multiplicative components must be separated by a “,” Examples

comp pow : Creates a power-law component for modeling the spectrum for all sectors that are present.
comp 2 pow : Same as above, but now the component is created for sector 2.
comp 4:6 pow : Create the power law for sectors 4, 5 and 6
com abs : Creates a Morrison & McCammon absorption component.
comp delete 2 : Deletes the second created component. For example, if you have 1 = pow, 2 = cie and 3 = gaus, this command delets the cie component and renumbers 1 = pow, 2 = gaus
comp del 1:2 : In the example above, this will delete the pow and cie components and renumbers now 1 = gaus
comp del 4:6 2 : If the above three component model (pow, cie, gaus) would be defined for 8 sectors (numbered 1–8), then this command deletes the cie component (nr. 2) for sectors 4–6 only.
comp rel 1 2 : Apply component 2 to component 1. For example, if you have defined before with “comp pow” and “comp “abs” a power law and galactic absorption, the this command tells you to apply component 2 (abs) to component 1 (pow).
comp rel 1 5,3,4 : Taking component 1 a power law (pow), component 3 a redshift operation (reds), component 4 galactic absorption (abs) and component 5 a warm absorber (warm), this command has the effect that the power law spectrum is multiplied first by the transmission of the warm absorber (5=warm), then redshifted (3=reds) and finally multiplied by the transmission of our galaxy (4=abs). Note that the order is always from the source to the observer!
comp rel 1:2 5,3,4 : Taking component 1 a power law (pow), component 2 a gaussian line (gaus), and 3–5 as above, this model applies multiplicative components 5, 3 and 4 (in that orer) to the emission spectra of both component 1 (pow) and 2 (cie).
comp rel 7:8 1:2 5,3,4 : As above, but only for sectors 7 and 8 (if those are defined).
comp rel 3 0 : Remove all relations from component 3.