Comparison of VO Spectrum and NED VOTABLE

[Jonathan McDowell]

For the record, I reviewed Joe Mazz's VOTABLE format returned by NED. It
contains no header metadata; the table columns contain some fields that
map directly to VO Spectrum fields, plus other fields that contain
non-machine-parseable  descriptions.

I give the mapping below. Their model really maps to two instances of
Spectrum, one (I'll call Spectrum0) in original published units and one
(Spectrum) in standard NED units.

There are three pieces of data that are mandatory in Spectrum but not
included in NED: the observation date, observation duration, and
the aperture size. The lack of these data do limit the scientific
usefulness of the NED SED VOTABLEs.

    - Jonathan


NED VOT format
Columns:
Name                         Type          VO Spectrum utype
--------------------------------------------------------------------------------
No                           Int.          (Just a counter)
Observed Passband            String        Spectrum.DataID.Bandpass
Photometry Measurement       Float         Spectrum0.Data.FluxAxis.Value
Uncertainty                  Float         Spectrum0.Data.FluxAxis.StatError
Units                        String        Spectrum0.Data.FluxAxis.Unit
Frequency                    Float         Spectrum.Data.SpectralAxis.Value
NED Photometry Measurement   Float         Spectrum.Data.FluxAxis.Value
NED Uncertainty              Float         Spectrum.Data.FluxAxis.StatError
NED Units                    String        Spectrum.Data.FluxAxis.Unit
Refcode                      String        Spectrum.Curation.Reference 
Significance                 String        (no equivalent)
Published Frequency          String        (no equivalent)
Frequence Mode               String        (no equivalent)
Coordinates Targeted         String        Spectrum.Char.SpatialAxis.Coverage.Location.Value
Spatial Mode                 String        (no equivalent)
Qualifiers                   String        (no equivalent)
Comments                     String        (no equivalent)


Mandatory VO Spectrum metadata not present in NED:

UTYPE                                               Value
Spectrum.Curation.Publisher                         implicitly NED
Spectrum.Target.Name                                parseable from <TABLE> name attribute
Spectrum.Char.FluxAxis.ucd                          fixed (for NED units) at "phot.flux.density;em.freq"
Spectrum.Char.SpatialAxis.Coverage.Bounds.Extent    Not available  (aperture size)
Spectrum.Char.TimeAxis.Coverage.Location.Value      Not available  (observation date)
Spectrum.Char.TimeAxis.Coverage.Bounds.Extent       Not available  (observation duration)