List of Observables for Observation Core components DM

[François Bonnarel]

  Hi Petr,
Thanks for you comments
See below some answers
François
Le 17/09/2010 21:08, Petr Skoda a écrit :
>
> 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.
No, I have seen maps with this quantity as observable in the Halpha 
Imaging domain.
> 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.
My guess was that the "jargon" expressed shortly the same idea. Have you 
a better shortcut? As Halpha is often using "interference filters" 
Continuum within the filter
can be considered constant (not really different from normalized ?) in 
this small range. Should we drop this instead and manage such 
singularities under a
miscelaneous ucd for the observable ?
>
> 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)
>
      Can we express that in term of observable? Look for a Ucd which 
tells that ?
> 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
>
> *************************************************************************
> *  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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>
>