Photometry and SED models at Nara

[Anita M. S. Richards]

Thanks for posting this Jonathan and for your work.

I am considering an 'aggregate' SED, originating from radio astronomy, 
where each point is in physical units (Jy per unit area).

I notice that the SED model refers to the Photometry model.  This is a 
very thorough description for optical or other 'magnitude' data; much of 
that can of source be skipped for radio but the point on Aperture 
Corrections could be extended to distinguish between the two common cases 
where the 
'unit' of area is the entire source, and where the unit is the beam area.

It would also be nice (and simple) to have a radio example.  One point - 
radio data is usually evenly spaced in frequency, I hope that we are not 
still only allowing wavelength?

Back to the SED, we should also consider the extensions to spectral index 
and spectral curvature (possibly higher orders) which are the coefficients 
for fitting a slope, a curve etc. to flux as a function of frequency 
(etc.)  For a 1-D spectral energy series these are single values. 
However, we should  also consider 3-D cubes where each plane is a map at a 
given frequency (like a 'line' spectral data cube, except not necessarily 
evenly spaced or of even interval); these can be collapsed to give 
spectral index (and higher order) 2-D maps.  I am not necessarily 
suggesting including these in the SED model! But we should recognise that 
these are common products and we should refer to SIAv2 which will (I hope) 
be able to include these by using Characterization - and make sure that 
the models are consistent.

Thanks very much

Anita



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Dr. A.M.S. Richards, UK ARC Node, Room 3.135
Jodrell Bank Centre for Astrophysics, Alan Turing Building, 
University of Manchester, M13 9PL
+44 (0)161 275 4243
and
MERLIN/VLBI National Facility, Jodrell Bank Observatory, 
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On Mon, 29 Nov 2010, Jonathan McDowell wrote:

>
> Mireille and Jesus,
> I have been asked to talk about SED data model issues in the
> SED session on Wednesday.
> I've put together drafts of Photometry and SED data models
> from my point of view (but with an attempt to incorporate the
> functionality of the ESAC approach) which I have posted at
> http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/DataModel
> and
> http://hea-www.harvard.edu/~jcm/vo/docs/index.html
>
> I've had some comments from Doug Tody and Arnold already,
> but have not yet incorporated them.
>
> I hope these documents will contribute to a useful starting
> point for our discussions. I look forward to seeing everyone
> next week!
>   Jonathan
>
> ;
>