[daip] aips setjy

[Eric Greisen]

Cao Hongmin wrote:
> 
> Hi Eric
> 
> VLBI dataset:
> 
> If the source is very strong, e.g. the flux density larger than several 
> *JY*,
> do we need use setjy to set the flux density of the source before we run 
> apcal (?)
> 
> If we don't do so, whether the amplitude calibration is still properly 
> calibrated ?
> (If we do so, the problem is how to find the total flux density of the 
> source,
> some sources may have variability)

VLBI amplitude calibration is done in a different way than VLA.  For 
VLBI, APCAL uses the system temperature information (plus gain curves) 
to generate amplitude scaling.  For VLA, the scaling comes from the 
ratio of the visibilities of point sources (or model sources) to the 
expected total flux of known calibrators.  GETJY is also used to take 
the flux of known calibrators and find the fluxes of more variable 
("unknown") calibrators.

You do not need SETJY at all for VLBI data.

Eric Greisen