[daip] some aips issues

[Eric Greisen]

Cao Hongmin wrote:
> Hi Eric,
> 
> i collect some aips issues note sure, hope you can give me a hand.
> 
> 1. in aips task "tysmo" , "aparm" can be used to do first clipping 
> before further smoothing,
> what kind of unit is used for "Tsys" ? (Kelvin or milli-Kelvin, it seems 
> the former).
>    how much does the Tsys deviate from the median value in , eg. one 
> several-minute scan, can be seen as abnormal?
> 
> 2. in task "clcor", "ANTC" can be used to correct the source position, 
> but i am ambiguous with the two terms: apparent source position and the 
> position of the epoch. does the former mean the position of the source 
> we see it today while the latter mean the position of the source in 
> J2000 Coordinates?
> 
> 3. i checked the delay/rate window by go prthi, which 4000 ns and 500 
> MHz respectively.
> the width of spectral line channel is 250 kHz, and the correlator 
> averaging time is 2 s.
> altough 1/250KHz right equals 4000 ns, but i am not sure the relation 
> between 500 MHz and 2 s.

Tsys is in Kelvin.  What a normal deviation is depends on the system - it
is best to determine it by looking at your data themselves.

"apparent source position" is position of date of observation and 
"position" or "position of epoch (or equinox)" is the B1950 or J2000 
coordinate.  Much of what we do is in the J2000 system - including the 
u,v,w values (so that the images are in J2000 coordinates).

the rate window is 500 milli Hz not MegaHz = 1/2.0 sec.

Eric Greisen