SED FITS Serialisation: multi-extension?

[Ivo Busko]

Doug Tody wrote:

<snip>

> While I agree that data model extensions will always be needed for special
> cases, if cases such as you mention here are important enough we should
> add it to the data model.  There is already support in there for background
> subtracted data.
> 
>         - Doug

There is a point here that perhaps should be taken into account when
evolving the SED Data Model into its next incarnation. The SED Data
Model 0.93 document states:

"The BackgroundModel array is required to have the same UCD and 
units as the Flux array." 

This is not the case with legacy data such as IUE and STIS. In these,
background data is expressed in uncalibrated units such as DN or 
counts/s. The SED DM should be more flexible and allow such data to 
be included in the SED-formated spectrum.

-Ivo

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