Standardising units and formats (and ref frames?) in transmission

[Alberto Micol]

Petr Skoda wrote:
>>> Or, I want data with a certain spectral resolution which I specify 
>>> in wavelength unts, but the data are in frequency units with a 
>>> non-linear conversion - i.e., the spectal resolution at one end of 
>>> the bandpass is different from that at the other, if the units are 
>>> changed.
>
> there is another catch here - the resolution in optical astronomy is 
> mostly considered the unit-less (spec. resolution power lambda/dlambda)
I would call that spectral resolving power, not resolution.
>
> whis is mostly constant over the long regions (e.g. echelle) but it is 
> still rough estimate. But the registry services still require the units
because it is a resolution not the resolving power what is requested there.
> but how to express it ?  in A/pixel ? If rebinned to 1D FITS (having 
> CDELT1=constant - its easy) but how about the red and blue part of 
> echelle spectra expressed in binary table ??)
> How to convert this for characterisation ???
>
I would probably allow both resolving power AND resolution, though in 
characterisation that
is expressed by both the location and the bounds of the "resolution":

- location provides a representative value (which in some cases 
coincides with the real and constant value
of the spectral resolution), 

- bounds provide the min/max values for such quantity
(important if the quantity varies on the spectral axis but also if it is 
constant, given that min=max will explicit
the fact that it is constant!)

Alberto
> Petr Skoda