Observing the Zone of Avoidance with ALFA - Commensality with GALFA

P. Henning, 13 July 2005, updated 17 March 2006  

As of now, we have observed commensally with with three GALFA projects:  
a2055 (Koo et al.) a2004 (Goldsmith et al.), and a2056 (Korpela et al.).

These are general instructions about how to do Zone of Avoidance (ZOA)
commensal observing with GALFA.  If ZOA is commensal with a project which
is considered "primary", then we need to communicate with the primary
to set up the following conditions for the wapps:

We need sky frequency set to 1383 MHz.  We chose 1383 based on experience 
with commensal observations with GALFA HI - this frequency allows them to 
avoid some interference which was folded into their narrow band, when we 
originally set the central frequency to 1385.  Thus, the first LO is 
1383 + 250 = 1633 MHz.  GALFA needs to set the second LO appropriately to 
get the Galactic HI into their band.

We use the wapps, with 100 MHz bandwidth.

We use a 1 second integration time.  

We want to have a calibrator at the beginning of each scan.  We use an ON-OFF 
cal pair.  When observing commensally with GALFA using basketweave mode, cals 
are fired at the beginning of each loop, and at the top as well.  This works 
fine for us.  If using drift scans, ask to fire a cal at the beginning of each 
drift.

So that data files don't get too big to handle, we need to have one loop
per fits file.  This parameter can now be set in basketweave mode in the
cima version 2.0.  I have also asked the GALFA primary project observers
to open a fits file before they do their smart frequency switching (SFS),
and then a new one before basketweaving.  That way, we can just ignore the
SFS data, which doesn't interest us, and is a conveniently in its own
file, not mixed up with data we want.    

If all of these conditions are set by the primary project, the observations
are very straightforward.  I have been watching to make sure that one loop
of basketweaving is written per fits file, and that the frequencies are set
correctly, and keeping track of what is in each fits file, eg. small junk
file, SFS, basketweave data.  I find using the Quicklook data display on 
the Dataview machine very convenient for watching wapp output.  Update the 
observing logs, for instance for a2056, at:
/share/zoa/zoa_a2056/a2056_obs_log.txt

The data are written to /share/wappdata under ID of primary project,
eg. /share/wappdata/wapp.20050710.a2004.0008.fits for the 8th fits file
written on 10 July for project a2004.  These files we run through LIVEDATA,
instructions in the document called "Data reduction for Zone of Avoidance
(ZOA) survey with ALFA - LiveData".