AIPS HELP file for QUFIX in 31DEC24
As of Fri Apr 26 12:14:14 2024
QUFIX: Task to apply Right - Left phase difference
INPUTS
INNAME UV data (name)
INCLASS UV data (class)
INSEQ 0.0 9999.0 UV data (seq. #) 0 => high
INDISK UV data Disk unit # 0 => any
IN2NAME Good image (name)
IN2CLASS Good image (class)
IN2SEQ 0.0 9999.0 Good image (seq. #) 0=>high
IN2DISK Good image disk unit 0=>any
IN3NAME Uncal image data (name)
IN3CLASS Uncal image (class)
IN3SEQ 0.0 9999.0 Uncal image (seq. #) 0=>high
IN3DISK Uncal image disk unit 0=>any
PCUT 0.0 Use only Q,U values > PCUT
in total polarization
NBOXES 1.0 50.0 Number of boxes for averaging
CLBOX -2.0 16384.0 Four coordinates for each box
CALIN
Text file with corrections
OUTTEXT
Text file w corrections
not blank => do not apply
HELP SECTION
QUFIX
Type: Task
Use: Performs the function of RLDIF to correct the BP, CP, and PD
tables in a spectral-line data set. These tables are produced
by BPASS and PCAL but are on separate phase references in the
two polarizations. This matters to cross-hand data. The best
way to correct this problem is with RLDIF. But that requires a
calibration source for which the Q and U spectrum or at least
the polarization position angle as a function of frequency is
well known. 3C286 is a good calibration source at all
frequencies, but 3C48, for example, has significant, but poorly
known polarization behavior at low frequencies and 3C147 has no
polarized signal at these same frequencies.
If you have images of a source which are well calibrated in Q
and U and wish to correct data from another day that lacks the
polarization position angle calibrator, QUFIX offers a
solution. It compares two 4-dimensional images (Ra, Dec, freq,
Stokes) to determine the rotation angle which will align the Q
and U on average as a function of channel. This angle may be
written out in a text file or simply applied to the tables of a
UV data set.
QUFIX offers the option of reading in a text file of
corrections determined from a previous run of QUFIX or from any
other method the user may devise. In that case, it does not
require or use the two image 4-cubes.
If your image is of a source with a spatially constant
polarization angle (e.g. a point source), then QUOUT and RLDIF
are better solutions for you. QUFIX is better used in the case
of complex sources with spatially variable polarization
position angle.
Adverbs:
**** Data set with tables to be corrected ****
INNAME......UV file name (name). Standard defaults.
INCLASS.....UV file name (class). Standard defaults.
INSEQ.......UV file name (seq. #). 0 => highest.
INDISK......Disk unit #. 0 => any.
**** Well-calibrated Stokes-spectral cube ****
IN2NAME.....Image file name (name). Standard defaults.
IN2CLASS....Image file name (class). Standard defaults.
IN2SEQ......Image file name (seq. #). 0 => highest.
IN2DISK.....Disk unit #. 0 => any.
**** Calibrated but not RLDIF Stokes-spectral cube ****
IN3NAME.....Image file name (name). Standard defaults.
IN3CLASS....Image file name (class). Standard defaults.
IN3SEQ......Image file name (seq. #). 0 => highest.
IN3DISK.....Disk unit #. 0 => any.
**** control parameters ****
PCUT........If determining the corrections from images, use only
pixels having SQRT (Q*Q + U*U) > PCUT in both image
cubes.
NBOXES......Number (<=50) of rectangular or circular boxes to search
in all Ra-Dec planes.
CLBOX.......A 4x50 array with the parameters of each box.
CLBOX(1,i)=-1 indicates a circle of radius CLBOX(2,i)
pixels centered on (CLBOX(3,i), CLBOX(4,i)).
CLBOX(1,i) >= 0 indicates a rectangular box.
CALIN.......Text file containing the corrections as angles in
degrees. - see below for format details.
If CALIN is not blank, the 2nd and 3rd images will be
ignored and the contents of CALIN used.
OUTTEXT.....Text file output containing the corrections. If OUTTEXT
is not blank, it will be used and no corrections will be
applied to UV extension tables (first UV file ignored
entirely).
NOTES:
1. Images 2 and 3 must be aligned in all axes.
2. Images 2 and 3 (or CALIN) do not have to be aligned in
frequencies with the UV data set. The corrections will be
interpolated to the UV data set frequencies.
3. CALIN must be in strict increasing frequency order.
CALIN file format:
1. Comment lines at any point begin in column 1 with either a
; or a # character.
2. Data lines contain the specified type of data columns:
frequency in GHz, polarization angle in degrees
Example:
# QUOUT run 12-JAN-2011 11:27:03 using CP version 2
# source is 3C286 with constant pol angle 33
# changed to corrections by 2 * (33 - pos ang)
#
# 4.988000000 32.97708 0
4.988000000 0.04592
# 4.990000000 32.97708 0
4.990000000 0.04592
# 4.992000000 33.01998 0
4.992000000 -0.03996
# 4.994000000 33.12441 0
4.994000000 -0.24882
# 4.996000000 33.31594 0
4.996000000 -0.63188
# 4.998000000 33.39096 0
4.998000000 -0.78192
EXPLAIN SECTION