List of Observables for Observation Core components DM

[Petr Skoda]

Dear Francois,

I have to comment this:

>    For the flux axis we distinguish observables for uncalibrated data from 
> the calibrated ones

I see you have "equivalent width" for "line intensities relative to 
continuum".

I do not understand this - maybe some radioastronomical jargoon.
In optical spectroscopy is the equivalent width the width of the rectangle 
that has the same integrated area of the profile as the original line and 
the height is put to be equal 1.0 IF we USE CONTINUUM NORMALIZED spectrum.

But this is a very subjective and derived product.
On the other hand the query for ObsTAP "give me all resources" having 
published continuum normalized spectra, would be the first I would expect 
from most stellar astronomers (and asking that I would be happy to get the 
maximal height of emission line on normalized spectrum in given line - 
e.g. to discover the known  outburst of Be stars - such a measurements 
are tabulated as well).

In SSAP we have restriction (although no one except my service provides 
this) FLUXCALIB=NORMALIZED

So if the ObsTAP should deliver useful information the concept of 
continuum normalized spectra  has to be solved as well. Then you can refer 
to EW as a measured variable ON SUCH spectra. The same the spectral moment 
(if you mean the higher moment of line profiles - the EW is the 0-th 
moment)

I may be wrong, however, so if anybody is able to measure EW on
non-normalized spectra, please, show us how.


BTW in the same sense the position of line (measured) is in fact derived 
value of observable which is put on characterization axis ....
(as the central position of the line is derived e.g by some cross 
corelation, mirroring of profile of fitting of curve through the 
observable points ....
Should we allow ObsTAP to query catalogues of measured line positions ?

We could start the whole discussion again about what is measurable (see 
RV;-) and what not - but I think the purity of design has to allow the 
practical queries as well.


>   Various special combined observables (equivalent width, and line ratio) 
> and polarized
>  fluxes come to complete this.

What is line ratio ? (something from radio?)
in optical there are so called Balmer decrements - the ratio of strenghts 
of Balmer lines (important for estimation of IS reddening) - but these are 
heights of the lines above the continuum level - again ..

I hope someone who has experience with spectral analysis will add more..

Petr Skoda

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*  Petr Skoda                         Phone : +420-323-649201, ext. 361 *
*  Stellar Department                         +420-323-620361           *
*  Astronomical Institute AS CR       Fax   : +420-323-620250           *
*  251 65 Ondrejov                    e-mail: skoda at sunstel.asu.cas.cz  *
*  Czech Republic                                                       *
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