[Passband] a useful self-contained model?

[Anita Richards]

> >  1 2 3 4 5 6 7 8     eight channels
> > | | | | | | | | |
> > -----------------
> > |----BANDPASS---|
> >
> > (here I use flux to include energy etc. and wavelength/frequency to
> > include freq., wavel., energy, wavenumber)
>
> Would this work if each channel was a separate Passband?  We might have a
> Passband that was a collection of other Passbands (ie what you've labelled as
> BANDPASS above) to make it easier to use collections of them.  I'll try and get
> some diagrams together on the page to make this clearer.

I think that would be overkill, at least in the (?majority?) of such cases
where the channels are the same apart from a displacement along the
wavelength (etc.) axis which is linear in the appropriate coordinate -
usually you talk about the entire bandpass which may or may not be
subdivided into n channels of x width... (or described by y Gaussian)
where x or y are the same for the entire bandpass.  There is then a
sensitivity function F(n)

> > an uncertainty if we are e.g. using linear bandpasses only.
>
> Hmmm; what I meant was that assuming getPassrate(wavelength) returns a
> probability value between 0 and 1 (inc), will you want that probability
> value to have an associated error? Will you want to give an uncertain
> wavelength?

I think that is what I was trying to explain - let's be mathematical:

Bandpass has centre x metres which has uncertainty (due to reference
wavelength standard) of deltax metres.  Probably not an issue for much
VO-accessible data at present but should be allowed to be added in
future.

However did you mean:
If I ahve understood you, getPassrate(wavelength) is approximated by F(n)
>
> Let us say we are using shaped bandpasses - would you need an error on the band
> shape then?
In some cases the exact form of F(x) may not be known,
or the effective bandpass may depend on the source being observed e.g.
the x-ray case.  So
leave room for errors - in fact as a general prnciple I would elave room
for errors in everything....


> >>  - Is 'passrate(Fravergy)', returning a value 0-1 probability, sufficient for
> >>Radio, X-Ray, etc?

Ah - a continuous function [0,1] or even ]0,1[ :)
>
> No I actually meant:
>
>    1|      xxx
>     |     x   x
> 0.5|    x     x
>     |  x       x
>    0 -----------------> Wavelength

>
> Which hopefully will clear up a lot of other comments you made!  Will people
> want any other characteristic than probability of transmission?

Indeed, thanks very much!

cheers

Anita