ObsTAPdraftDiscussionRadVel < IVOA

Use case 3.2 and 3.4 directly include constraints in radial velocities. It is a typical feature of some radio or interferometry cubes observing a single line to give measurements  of fluxes  for a given 
spatio-radvel coordinate or spatio-redshift coordinate.
   
Discussion in Nara initiated by Arnold and Igor showed that most people consider the RadVel axis to be different from the spectral axis. The argument being that we are facing two non permutable quantities as long as we are not considering a single , isolated spectral line.

Upcoming version 2 of characterisation DM will add a new RadVel or Doppler axis. It would be perfectly possible to add a couple  of optional fields allowing to search against "radial Velocity" bounds and resolution...

This is the minimum required to fulfill  the use cases 3.2 and 3.4.

-- IVOA.JuanDeDiosSantanderVela - 16 Mar 2011

In order to make a concrete proposal, I would propose the following fields:

   * =vel_min=: Minimum value of the line-of-sight velocity. Positive values indicate receding velocity.
      * Mandatory: NO.
      * datatype: adql:DOUBLE
      * Can be =NULL=: YES
      * UCD: phys.veloc;stat.min
      * Unit: m/s
      * UType: to be discussed; could be =Char.VelocityAxis.Coverage.Bounds.Limits.Interval.LowLim=

   * =vel_max=: Maximum value of the line-of-sight velocity. Positive values indicate receding velocity.
      * Mandatory: NO.
      * datatype: adql:DOUBLE
      * Can be =NULL=: YES
      * UCD: =phys.veloc;stat.max=
      * Unit: m/s
      * UType: to be discussed; could be =Char.VelocityAxis.Coverage.Bounds.Limits.Interval.HiLim=

   * =vel_resolution=: Velocity difference average or reference bin size.
      * Mandatory: NO.
      * datatype: adql:DOUBLE
      * Can be =NULL=: YES
      * UCD: =phys.veloc; spect.resolution=
      * Unit: m/s per bin
      * UType: to be discussed; could be =Char.VelocityAxis.Coverage.Resolution.refVal=

I do not like the term Radial Velocity, as it implicates a geometry in the object. Line-of-sight velocity (or plain Velocity, as in the proposal) seems better and cleaner to me.







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This topic: IVOA > WebHome > IvoaDataModel > ObsDMCoreComponents > ObsTAPdraftDiscussion > ObsTAPdraftDiscussionRadVel
Topic revision: r3 - 2011-03-16 - JuanDeDiosSantanderVela