Simple spectral model revision

[Arnold Rots]

I think it would be reasonable to effectively follow the Green Bank
convention, replacing a keyword by a column and naming that column by
the keyword name:  TTYPEm = 'TUNITn'

  - Arnold

Ivo Busko wrote:
> I think there is an inconsistency between the VOTable and
> FITS serializations described in the IVOA SED Data Model
> (v 0.93).
> 
> The VOTable serialization allows the option of writting
> data for each individual segment, with its own set of
> physical units (for both spectral coordinate and flux
> values). 
> 
> The FITS serialization apparently does not allow for that.
> Multiple rows in a table (meaning, multiple segments) are
> required to share the units instance associated with each 
> column.
> 
> When writing a SED assembled from multiple data sources,
> I believe it is desirable to keep each segment in its
> own "native" units, instead of transforming everything to
> a common set of units. And what that common set would be?
> It is not specified in the data model to begin with.
> 
> Note that the SED model allows for independent UCDs for
> each segment/row (SPO_UCD and FLUX_UCD columns. However, 
> assuming that UCDs can change from row to row, doesn't mean 
> that units have to change from row to row as well?
> 
> A possible solution would be to add extra columns to the
> SED model in order to hold the units. However, this might 
> violate the FITS standard that requires units to be a part
> of the column dscriptor itself. Or am I wrong in assuming
> this?
> 
> Any ideas?
> 
> Regards,
> 
> -Ivo Busko
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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