This attribute identifies the spectral system in which the
SourceVel attribute value (the source velocity) is supplied and
returned. It can be one of the following:
When setting a new value for the SourceVel attribute, the source
velocity should be supplied in the spectral system indicated
by this attribute. Likewise, when getting the value of the SourceVel
attribute, the velocity will be returned in this spectral system.
- "VRAD" or "VRADIO": Radio velocity (km/s)
- "VOPT" or "VOPTICAL": Optical velocity (km/s)
- "ZOPT" or "REDSHIFT": Redshift (dimensionless)
- "BETA": Beta factor (dimensionless)
- "VELO" or "VREL": Apparent radial ("relativistic") velocity (km/s)
If the value of SourceSys is changed, the value stored for SourceVel
will be converted from the old to the new spectral systems.
The default value is "VELO" (apparent radial velocity).