[Obscore Update v1.1] an attempt to describe the Redshift Axis

[Arnold Rots]

I have to apologize for having procrastinated so long on this issue.

I would prefer to stick with redshift, rather than doppler, and use rs or
reds.
It's a matter of consistency with standards.

One could probably get away with using three definitions:
REDSHIFT, OPTICAL, and RADIO.

But the reference position is crucial, since common defaults vary
with definition. and one should realize that for the redshift axis the
reference position should be interpreted as a state vector, not just
a 3-D spatial position.

Typically, BARYCENTER will go with REDSHIFT and OPTICAL, and
will mainly be used for extragalactic work.
LSR or BARYCENTER will be used for  Galactic work, often in
combination with RADIO. However, there are examples (even from
people who know better) where these values have been mixed in
an unacceptable fashion, so one needs to be explicit about this stuff.

Cheers,

  - Arnold

-------------------------------------------------------------------------------------------------------------
Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------------------------------------------



On Fri, Mar 7, 2014 at 2:34 PM, Louys Mireille <mireille.louys at unistra.fr>wrote:

>  Dear DMers, dear all,
>
> Here is an attempt to add Redshift Axis description in the Obscore Data
> model summary table.
>
> I suggest to use *d_*  as the prefix for *doppler *measurement.
> DopplerAxis is another word for Redshift Axis , but seemed general enough.
> The doppler features roughly have the same kind of list structure as the
> spectral axis list items in Obscore.
>
> The definition of the Doppler axis is included , plus the reference of
> phase origin. (green lines in the table)
>
> This raises the question of other axis reference positions , which were
> not included explicitely  in the previous Obscore recommendation, but
> defined implicitely by default ( ICRS, TT, TOPOCENTER) I suppose. Please
> correct me if I am wrong.
>
> Here is my question to the WG:
> Would it be sufficient instead to combine all the reference positions of
> the various axes together via the *coord_system_id*  defined in the STC
> recommendation at Appendix C1. for AstroCoordinateSystem ID .
>
> It seems to me that <AstroCoords coord_system_id="TT-GAL-RADIO-LSR-TOPO">
> as used in the STC example ARECIBO appendix C of the STC recommendation ,
> tells all the reference stamps necessary for the various coordinate frames.
> Am I wrong?
>
> If this would work then
> - only one reference to the appropriate coord_system_id might spare the
> various references and definitions on each axis.
> - we could have a default coord system id definition for data discovery.
>
> Comments , questions welcome ...
> Cheers , Mireille
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.ivoa.net/pipermail/dm/attachments/20140328/8330319b/attachment.html>