Photometry in VO Spectrum Model
jcm at head.cfa.harvard.edu
Sun Oct 22 17:00:50 PDT 2006
I don't now recall who requested this at the Tucson meeting.
The idea was that the Spectrum model is also very close to being
a model for photometry, and especially for SEDs we would like to
be able to mix spectra and photometry points.
However, photometry observers like to report their data
in magnitudes, even when it is absolutely calibrated. They want
I measured a J magnitude of 11.8, and to convert my J to Jy
(ignoring color term effects) you do F = F0 * 10**(-0.4 * J)
where F0 is given in the header
rather than calculating F themselves and putting that directly
in the data.
Of course you'd like to point to the whole transmission curve
yourself; then you can calculate the flux F from the magnitude J
making your *own* (client side) assumptions about the object spectrum.
Hence the URI.
I guess the real science justification is that J is a calibrated
value; F is more than that, it's a modelled flux making an assumption
about the source spectrum. So better to publish J than F as long as
you can get F easily.
It seems a small thing to add to the model, and wins us a lot of
archival photometry. We discussed this around the table in Tucson
and you didn't seem bothered then...
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