Comments on Spectrum Data Model 0.9

[Anita Richards]

>
> However, outside the scope of a webservices infrastructure,
> Anita's concerns are still valid. Presently I wouldn't know
> how to handle them.
>
> -Ivo

Thanks very much Ivo,

Now I am much happier!

It does imply that with such good models we can now beging to concentrate
more in DAL on helping people to publish data i.e. building the
webservices infrastructure, what the science drivers need and how to make
it easy for people who run data archives to provide the right stuff.

> Well, there is a single minor point where the model and
> the "real data" I used disagree: data providers usually
> do not care to calibrate the background data to flux
> density units. The few formats that allow for a background
> array (STIS, IUE, ACS) provide then in some sort of raw
> counts. Thus if the requirement in paragraph 4.4 of the
...

Regarding units, that is an issue which has to be tackled; it is more
general than this model but it is a real obstacle to a) working with
unfamiliar data sources b) working across the whole e-m spectrum.

I know that very accurate conversions to physical units can be complex and
even in e.g. the radio-sub-mm domain where everything is usually in
physical units, aperture size is an issue.  And even without conversion,
even raw counts are useful for knowing if a line is present or for
finding ratios.

NED appears to solve it for b) by using hard-wired conversions, which also
means that it is usually very out of date but none-the-less still very
useful if you want to know e.g. the typical radio:x-ray ratio of a certain
class of galaxy, etc.

So it should not be too difficult for VOs to build up a library of
quick'n'dirty conversion factors, with some sort of warning that they are
not highly accurate, but for many purposes would be extremely useful, e.g.
starting with the main HST, Chandra and XMM bands....

However maybe that and the aperture issue are questions for Apps, not this
WG...

cheers
a

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Dr. Anita M. S. Richards, AVO Astronomer
MERLIN/VLBI National Facility, University of Manchester,
Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, U.K.
tel +44 (0)1477 572683 (direct); 571321 (switchboard); 571618 (fax).