Radial velocity curves

[AdaNebot]

There is no proposed annotation for radial velocity curves, despite this type of time series being the second mayor existing type.
The document could also propose the structure and minimum metadata for a GROUP for radial velocity curves.

[AdaNebot]

A GROUP for the metadata of VELOCITY, would need the following elements:

• velocity: an attribute that defines the type of value. Allowed values are VELOCITY and REDSHIFT
• definition: an attribute to allow to translate redshift to doppler Velocity. Allowed values are OPTICAL, RADIO, RELATIVISTIC (Need to check this)
• refPosition: an attribute for the reference position. The values SHOULD be taken from the IVOA refposition vocabulary http://www.ivoa.net/rdf/refposition. The other possible values are LSR, LSRD, GALACTOCENTRIC, LOCAL_GROUP_CENTER. This attribute is mandatory.

Action: check that this elements and their possible values are in agreement with STC.

[AdaNebot]

Despite the metadata being identified, I propose to finish the light-curve case first. Once that done, we can re-think about this.