Alfacal

Alfacal is a utility for accessing the ALFA spectral parameters and calibration determined by Desh by providing an interface to his fortran subroutine. See Desh's memo for a description of how the paraemeters were derived.

To run Alfacal at AO, type
~rminchin/progs/alfacal ⟨centrefreq⟩ ⟨bandwidth⟩ ⟨option⟩ ⟨zenith angle⟩
Where:

• ⟨centrefreq⟩ (default 1380 MHz) is the central frequency (in MHz) of the observation for which the parameters will be determined;
• ⟨bandwidth⟨ (default 80 MHz) is the bandwidth (in MHz) to average over around this centre frequency — note that it is usual to use 80% of the bandwidth of any observation, not the full bandwidth;
• ⟨option⟩ (default GAIN) is one of GAIN, SEFD, TSYS or TCAL and selects which of these to measure;
• ⟨zenith angle⟩ (default 5 degrees) is the zenith angle at which to determine the parameter (this is ignored if it is outside the range accessible at AO of if ⟨option⟩ = TCAL).

The output gives the value and the error for each beam and polarisation (note that the error is the error on the points averaged across the bandwidth and does not include any error in the zenith angle correction). It is formatted as follows:

 Gain over   80. MHz centred on   1380. MHz at ZA =   5. degrees.
 ZA correction factors:   1.  1.
 Beam  0:  Pol 1  Pol 2
 Value:   11.1839018  11.1677742
 Error:   0.0305875093  0.0309901554
 Beam  1:  Pol 1  Pol 2
 Value:   8.70151711  8.48216057
 Error:   0.0294616111  0.0266611632
 Beam  2:  Pol 1  Pol 2
 Value:   8.86137962  8.92475986
 Error:   0.0264299996  0.0278139934
 Beam  3:  Pol 1  Pol 2
 Value:   8.23973179  8.23015118
 Error:   0.030120587  0.0266778171
 Beam  4:  Pol 1  Pol 2
 Value:   8.51489735  8.40820503
 Error:   0.0296856202  0.0287898406
 Beam  5:  Pol 1  Pol 2
 Value:   9.25692749  8.89543724
 Error:   0.0294356942  0.0314402729
 Beam  6:  Pol 1  Pol 2
 Value:   8.97087383  8.80161095
 Error:   0.0295731761  0.0271398723

Note that the ZA correction factors are given with respect to a zenith angle of 5 degrees, which is the zenith angle to which the calibrations have been normalised.

Installing Alfacal

Alfacal should run fine at Arecibo, if you want to run it elsewhere you need to make a local installation. To install Alfacal, you will need to download and unpack the datafiles in ALFA_POLY_FITS.tar.gz. You then need to download the fortran sourcecode for Alfacal, alfacal.f and change the section:

c     Alter this bit if the ALFA_POLY_FITS files have been installed in 
c     a different directory.
      character*39 path
      path='/share/rminchin/alfacal/ALFA_POLY_FITS/'

so that ‘path’ points to the directory in which you have installed the ALFA_POLY_FITS files and has the exact length required (set character*N path where N is the length of the pathname).

Now simply compile the program using, e.g., f77 alfacal.f -o alfacal and you should be able to run it using the above instructions.