List of Observables for Observation Core components DM

[Patrick Dowler]

On Tuesday 07 September 2010 14:23:04 Mireille Louys wrote:
> please look at
> http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/ObsTap

Comments from various astronomers in CADC:

--
You're missing "scaled counts".... You could argue that they are the same
[as ADU] from a philosophic point of view, but to an astronomer, they mean 
something different.
--
The units of flux density are Jy, not Jy/Hz.
So also flux surface brightness in your table should be named flux 
density surface brightness.
--
And, to make life more complex, most radio continuum measurements are
actually phot.flux.sb, with the intensity integrated over a passband,
that people scale into Jy units on the assumption that the emission does
not vary much across the passband.  

For fields that do not include much extended emission, it is common to
scale the image as a surface brightness in Jy per beam.  This is very
handy when the fields include point sources whose flux can then be read
directly from the peak "surface brightness", but is an abomination for
extended sources whose spacially integrated fluxes must be scaled by the
effective beam area.

Also, radio heterodyne observations are typically reported as antenna
temperatures Ta* in K.  For spectra and datacubes, the assumption is
implicitly made that the emission is extended spacially on the scale of
the main beam, and is more broad-band then the frequency resolution.

Again, for heterodyne observations of spectral lines, it is common to
give "integrated intensities", in which the energy axis is reported in
radial velocity units rather than frequency or wavelength, so the
integrated intensity units are K km/s.
--

-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2M7

Centre canadien de donnees astronomiques
Conseil national de recherches Canada
5071, chemin West Saanich
Victoria (C.-B.) V9E 2M7