relative fluxes

[Douglas Tody]

On Tue, 23 Jun 2009, Alberto Micol wrote:
> 
> As demonstrated by this long discussion, it is clear that all the above
> requires clarification in the SpectrumDM text.  This kind of confusion
> (in this and other standards) is killing all our efforts.  We have to
> be precise, and to provide clear and unambiguous (almost mathematical)
> definitions, accompanied by a good set of real (as opposed to virtual)
> examples (tutorials). Revision of the IVOA documents should take into
> account the confusion that certain definitins might introduce in the
> (even vo-aware) data providers. Crystal-clear documents are an art;
> we are good, but apparently not in Arts...

What we most need now are *implementations*, with real data, of both
SSA services and client applications which begin to use the information
in the SpectrumDM.  After there have been a few more of these we will
have enough experience to update the SSA/SpectrumDM specifications
and address most of these subtle issues.  Adding a user guide could
also be very useful.

If applications do not present this information well to the user
that should be addressed as the applications are updated to be
more VO-aware.  This won't happen until we have more, better, more
compliant SSA services.

> Did the FITS community ever tried to describe this?  Why isn't there
> a BCALIB = 'RELATIVE' / or ABSOLUTE or UNCALIBRATED or RECTIFIED
> FITS keyword?
> 
> Shall we reccomend one? (Haven't I just done that? ;-))

Note the SSA/SpectrumDM data model spreadsheet suggests FITS keywords
for many of the data model attributes (the HST/MAS SSA services for
example are already using these):

     https://webtest.aoc.nrao.edu/ivoa-dal/ssap-keywords.xls

For the FLUX calibration attribute we have FLUX_CAL (also TIME_CAL
etc.).

 	- Doug