[SPECTRUM] Revised spectral data model

[Anita Richards]

Thanks Jonathan, it looks a good start.  I thought I should document some
of the heckles I raised....

We need some more general terms for concepts like
1)equivalent width
2)pixel

which only apply to some kinds of data, other terms are omitted in this
model.

1) is not always meaningful
e.g. HI absorption has other important parameters like spin temperature

So either we need to distinguish between terms of more-or-less universal
applicability like the e-m/energy spectral units (table under 6, which
could easily be extended to cover particle energy spectra), and terms
which are only used in some regimes.

Thus
7. Linelists
I suggest that we contribute the different sorts of linelists which are in
common use or are associated with current major science issues, and then
try and generalise.  e.g. a typical spectrum may be lots of different
species' transitions as described, or they may be many transitions from
one species, or it may be one transition showing complex velocity
structure (the latter applies often at radio freq) or ???.  I don't have
an answer except that we should keep observed properties (freq, FWHM etc)
separate from interpretative properties (asignment to a species, velocuty
model etc.)

If we do end up using terms which normally have a narrow meaning, we
should define them for our context.  We should not try and be artificially
comprehensive, just unambiguious.

2)
"pixel"

Is this a unit of measurement on the spectral axis? of freq (or analogue)?
Or spatial position? Or intensity? e.g.  radio people are used to thnking
of frequency channels, I don't mind using pixels but I need to make sure I
know what the term means.

thanks

Anita


- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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).