Spectral 2.0 - Document update

[Arnold Rots]

Petr,

Regarding your second point, that is one more reason why wavelength is such
a bad choice for spectral coordinates. Frequency makes much more sense and
has the advantage that its conversion to the third type, energy, is linear
- it's two against one :-)
But you alerted me to the fact that I need to add another property to the
wavelength variant of the spectral coordinate in STC2.

Cheers,

  - Arnold
On Jun 4, 2015 8:46 PM, "Petr Skoda" <skoda at sunstel.asu.cas.cz> wrote:

> Hi Mark and all DM members
>
> Unfortunately I do not have time to go through tiny details of SDM 2.0
> But I would like to be assured (by you) that there is a simple answer to
> these issues:
>
> 1) normalized spectra -  I mean continuum normalized (i.e the horizontal
> line of continuum is at 1.0)
> Those do not have by definition units - its just relative ratio - it was
> somehow defined in older SDMs as a ration and some reference (but no one
> defined yest how to refer to the description of contiuum) - in practise all
> usefull optical spectra should be continuum normalized by pipeline (or
> manually) already before ingesting in SSA services ....
> How to describe the Fluxunit and UCDs on flux etc ..... ?
>
> 2) The wavelength of practically all optical spectra from ground (et least
> those in current SSA services) is a wavelength in AIR !!!
> It is exactly what comes out of pipelines and reflects the observing
> conditions (temperature, humity ...) .
> The conversion to vacuum wavelengths is not trivial and requires some
> provenance values .... and moreover it would not be much useful for most
> people as they know (by heart) only air wavelengths and expect them ....
>
> But SDM and SSAP define implicitely all wavelenghts in vacuum ....
>
> So in principle all current SSA services are faked !!! They are not
> compliant at all with standards ...
>
> The (hacked) solution is to deliver label on X axis as "air wavelength"
> but in principle we may not use the current SDM and SSAP with calm minds
> ....
>
> 3) SDM2 and SSAP2 aspire to be able to handle the time series ...
> then the spectral units should be time units, bands as wavelength ranges
> are changing into formal description of photometric filters (and somehow
> converted to real band ranges) - there was a discussion last year ...
>
> is this possibility reflected in definiton of axes and their labels ?
> I suppose we should tacle this in Sesto  ....
>
>
> Best regards
>
> Petr
>
> *************************************************************************
> *  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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>
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