SED Data Model: Questions and Comments

[chil at sai.msu.su]

Hello,

On Wed, 2 Feb 2005, Jonathan McDowell wrote:
> 2. No flux calibration.
> I'm still thinking about this one. In your case (shape right,
> flux cal absent) one could just put a huge systematic error
> bar on, but it would be better to have a special tag.

I don't think a huge systematic error bar is a good solution,
because somethimes even the order of magnitude is unknown.

The question connected to the flux calibration is handling "observed" fluxes
(FLUX-OBS in FITS) -- that are obtained with the ground-based observations,
and "physical" (FLUX-PHY) fluxes -- ones outside atmosphere. The correction
could be made in both directions if one has some extra metadata: meteo (temp.,
humidity, pressure, ...) and "obs. run-time"  (airmass, transparency or
extinction on a given wavelength, ...)

> 3. Atmosphere and vacuum wavelengths
> what extra metadata do you need to let applications make the correction
> from air to vacuum? Airmass, temperature, humidity, ...??

There is an IAU standard (!), that doesn't care of meteo params.
It tells (Morton 1991,ApJS,77,119) that
      AIR = VAC/(1.0 + 2.735182E-4 + 131.4182/VAC^2 +  2.76249E8/VAC^4)
where AIR and VAC are lambda-s in Angstroms. Should we follow it, or we should
implement something better (if exists)?

> 4. Resolution and line spread functions
> resolution function. I think what we need to do is define
> a standard VO way of defining parameterized functions
> (maybe with XML type name VOFunction), and a way of

It is a good idea! But this will require a standard way to access such
data, as you mentioned. What I can propose, is to define a kind of
"resource-discovery" approach. First step is to make a query to a
resource returning, say, a VOTable containing the function names, text
descriptions, and references to WSDL for accessing them. The second step is to
access these functions as normal WebServices. If we use this approach, it will
allow to handle tabulated functions as well. What DAL people think about it?

With best regards,
						Igor