What a ride. As it turns out, I did a lot of research on parallactic angle calculations. You can read about most of this here!

Compute the parallactic angle, Q, for a CAT image. Actually, I wrote two versions of this. The first, called cat2qlist takes an input list of files and positions (see below) and derives the parallactic angle and position angle for each of them. In the cat2q routine, I simply read the input on the command line for one image. In the cat2q version I use a way to get variables assigned from runs of other scripts (as opposed to writing to an intermediate file), and I use a formatted printf. So, I iclude the source for BOTH of these scripts below.

% ls
Expected.Q  list.1  README  S0/

%  cat list.1  
20140219T030632.1_cat_sci.fits  07:27:25.80 +66:19:54.0
20140219T031453.4_cat_sci.fits  06:12:51.10 +65:43:06.0
20140219T044549.8_cat_sci.fits  08:30:15.90 +60:43:05.0
20140219T051011.5_cat_sci.fits  09:25:44.20 +63:56:27.0 
20140219T053130.2_cat_sci.fits  08:30:15.90 +60:43:05.0

Usage: cat2qlist list.1 N 
arg1 = input list of [image,Ra,Dec] values 
arg2 = "Y" for verbose output  

%  cat2qlist list.1 N  
07:27:25.80 +66:19:54.0 20140219T030632.1_cat_sci.fits
06:12:51.10 +65:43:06.0 20140219T031453.4_cat_sci.fits
08:30:15.90 +60:43:05.0 20140219T044549.8_cat_sci.fits
09:25:44.20 +63:56:27.0 20140219T051011.5_cat_sci.fits
08:30:15.90 +60:43:05.0 20140219T053130.2_cat_sci.fits

Your answers are in the files:   list.Q and list.catPAdeg

% ls
a      junk2  list.1         list.DECdeg  list.HAdeg  list.Q      list.ST  S/
junk1  junk3  list.catPAdeg  list.DECsex  list.LST    list.RAsex  pars.in

% cat Expected.Q 
29.13
359.27
18.74
28.69
359.35

% cat list.Q 
 29.13 
 359.27 
 18.74 
 28.69 
 359.35 

You can run a test of this in $tdata: 
/home/sco/sco/projects/Test_Data_for_Codes/T_runs/cat2q/ex1

 
 
#!/bin/bash
# Compute parallactic angles for McDonald Obs. CAT images 

# Check that an argument is present
if [ -z "$1" ]
  then
    printf "Usage: cat2q 20140219T030632.1_cat_sci.fits  07:27:25.80 +66:19:54.0\n"
    printf "arg1 = CAT image fits file name  \n"
    printf "arg2 = RA in sexigecimal format  \n"
    printf "arg3 = DEC in sexigecimal format  \n"
    exit 1
fi

# Put commandline arguments into easy varaible names 
catname="$1"
RAsex="$2"
DECsex="$3"
#printf "$RAsex $DECsex $catname\n" 

# Construct the isot date/time strings 
isot=$(cat2isot.sh $catname)
#printf "ISOT string: $isot\n" 

LST=$(mcdLST.py $isot) 
#printf "local sidereal time (LST) string: $LST\n" 
# Write the LST string to a file for run for sexprep
echo $LST > list.LST
# prepare the ST file (clean the sexigecimal) 
STsex=$(sexprep.sh list.LST)
#printf "clean local sidereal time (LST) string: $STsex\n" 

# Compute the HA
HAdeg=$(cal_from_sex_HA.py $RAsex $STsex) 
#printf "HA(degrees) = $HAdeg\n" 

# get DECdeg
DECdeg=$(sex2float.sh $DECsex) 
#printf "DEC(degrees) = $DECdeg\n"

# Compute the Q
Q=$(mcd_parallactic_angle $HAdeg $DECdeg)
#printf "Parallactic angle (Q) = $Q \n"

# Compute CAT PA 
PAdeg=$(q2catpa.sh $Q)
#printf "CAT position angle (PA) = $PAdeg\n"

printf "%9.3f  %9.3f\n" $Q $PAdeg

# Do some clean up 
#\rm -f junk1 junk2 junk3 pars.in

The cat2qlist script may be more useful for processing a long list of images. I include the source here.

 
 
#!/bin/bash

# Compute parallactic angles for McDonald Obs. CAT images 

# Check that an argument is present
if [ -z "$1" ]
  then
    printf "Usage: cat2qlist list.1 N \n"
    printf "arg1 = input list of [image,Ra,Dec] values \n"
    printf 'arg2 = "Y" for verbose output  \n'
    exit 1
fi

# delete files from a previous run 
\rm -f list.RAsex list.DECsex list.LST list.ST list.Q  
\rm -f list.DECdeg list.HAdeg list.catPAdeg

# Create individual lists of LST,RA,DEC (all in 
# sexigecimal string format) 
i="0"
# Read each line in the input file (= $1)
# using file descriptor 3
exec 3<$1
while read -u3 catname RAsex DECsex 
do 
 i=$[$i+1]
 printf "$RAsex $DECsex $catname\n" 
# Construct the isot date/time strings 
 cat2isot.sh $catname >a
 read isot > list.LST 
# Write to the Ra,Dec list files 
 printf " $RAsex \n" >> list.RAsex
 printf " $DECsex \n" >> list.DECsex
done 

# prepare the ST file (clean the sexigecimal) 
sexprep.sh list.LST > list.ST 

# Now process each line in the list.RAsex, list.DECsex
# list.ST files you have just built 
i="0"
# Read each line in the input files (= $1, $2, $3)
# using file descriptor 4
exec 3 junk1
 read HAdeg < junk1
 printf "  $HAdeg  \n" >>list.HAdeg 

# get DECdeg
 sex2float.sh $DECsex > junk2
 read DECdeg < junk2
 printf "  $DECdeg \n" >>list.DECdeg

# Compute the Q
 mcd_parallactic_angle $HAdeg $DECdeg > junk3
 read Q < junk3
 printf " $Q \n" >>list.Q

# Compute CAT PA 
 q2catpa.sh $Q >>list.catPAdeg

 if [ "$2" = "Y" ]
 then 
  printf "$STsex $RAsex $DECsex\n" 
  printf "HA (degrees) this image  = $HAdeg\n"
  printf "DEC (degrees) this image = $DECdeg\n"
  printf "Parallactic angle, Q     = $Q\n"
 fi 
 
done  

# Do some clean up 
#\rm -f junk1 junk2 junk3 pars.in

 

Notice above that the first thing we do is read the input list and create files of RA,DEC and LST. The LST are computed with the routine mcdLST.py after I generate the ISOT time string with cat2isot.sh. Next, we process these file to generate the Q values written to list.Q. Finally, the custom (OTW) code called q2catpa.sh is used to transform parallactic angles (q) to the CAT position angles (in list.catPAdeg). With these final PA values, I can generate North vectors in the CAT images shown below.

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Practical examples of cat2q.

Below I show some results of practice runs (in my Test_Data directories) of cat2q. These examples are found in:

 
$tdata/T_runs/cat2q/ex0

In the left panel I show the raw CAT image of NGC2355 (jan17_2015). This image (20150117T041016.0_cat_sci.fits) was processed with the cat2q script to compute the q and PA. The PA=220 value I "drew in by hand" above using a ds9 vector marker. In the right panel I show a smoothed version of this image that had WCS that was processed by astrometry.net. You can see in the small sub-window in the upper-right that the North vector for this WCS agrees approximately to that predicted with cat2q. It is useful to record the ds9 regions file I used to generate the North marker in the left panel: % cat ds9.reg # Region file format: DS9 version 4.1 # Filename: 20150117T041016.0_cat_sci.fits physical # vector(822.93276,621.97311,492.04,312.709) vector=1 color=white width=4 text={North} Note that the last two arguments for a vector are the length and the angle. The angle for a ds9 vector is measured CCW from the +X axis.

Much like above, but with NGC869. The vector drawn in both panels was generated (n.reg) manually to give a vector pointing at CAT_PA = 44 deg. This would correspond to a ds9 angle = 134 deg.

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