Scripts for Step 4 - Prepare the lines:

• step4_prepare_lines.py # main script

• step4_detour.py # for phase alignment

• dictionary_data.py # loads data_dict

• step1_utils.py # loads multiple functions

• analysisUtils (analysis_scripts/) # for channel strings

Apply Phase Shifts

In Step 2, we used the continuum to compute the phase shifts necesssary to align our execution blocks. Here we simply take those pre-computed offsets and apply those same shifts to the line MSes. We take a “detour” from the main step4_prepare_lines.py script to the step4_detour.py in order to work in modular CASA. We again do the alignments in two steps (long baseline data, then short baseline data), though we could have fed in all MSes in one call.

Align Long-Baseline Execution Blocks

EB	R.A. offset (arcsec)	Dec. offset (arcsec)
LB EB 1	0 (ref)	0 (ref)
LB EB 2	-0.0198	+0.0047
LB EB 3	-0.0127	+0.0013
LB EB 4	+0.0237	-0.0219
LB EB 5	-0.0207	-0.0105
LB EB 6	-0.0046	-0.0276

Long baseline execution blocks: Phase offsets between the phase center of each EB and the reference (LB EB1) found in Step 2.

1. Select the reference execution block. We are not computing any phase offsets here, but the code requires feeding in a reference.

reference_for_LB_alignment  = ddata.data_dict['LB_EB1']['_initlines.ms']

It’s not necessary to specify the continuum spectral window ID or set the grid this time.

2. Set the offsets to be applied (from Step 2).

alignment_offsets   = []
#insert offsets from the alignment output
alignment_offsets.append([0,0])
alignment_offsets.append([-0.019783,0.0046808])
alignment_offsets.append([-0.012707,0.001336])
alignment_offsets.append([0.023685,-0.021869])
alignment_offsets.append([-0.020729,-0.01054])
alignment_offsets.append([-0.0045512,-0.0276])

3. Apply the shifts.

alignment.align_measurement_sets(reference_ms       = reference_for_LB_alignment,
                                 align_ms           = offset_LB_EBs,
                                 align_offsets      = alignment_offsets)

4. Check that it worked. The “RA”, “Decl” and “Epoch” columns in each EB’s listobs should be “04:55:45.854900 +30.33.03.73320 J2000”.

"""Check that the phase center of each EB is: 04:55:45.854900 +30.33.03.73320 J2000"""
for EB in ddata.data_dict['LB_EBs']:
    vis          = ddata.data_dict['NRAO_path']+ddata.data_dict[EB]['_initlines_shift.ms']
    casatasks.listobs(vis=vis, listfile=vis+'.listobs.txt')

Align Short-Baseline Execution Blocks

EB	R.A. offset (arcsec)	Dec. offset (arcsec)
LB EB 1	(ref)	(ref)
SB EB 1	-0.0131	+0.0395
SB EB 2	+0.1192	-0.1922

Short baseline execution blocks: Phase offsets between the phase center of each EB and the reference (LB EB1) found in Step2.

5. Repeat the above steps 1-4 but with the SB phase offsets and SB MSes.

alignment_offsets   = []
#insert offsets from the alignment output
alignment_offsets.append([-0.013133,0.03949])
alignment_offsets.append([0.11922,-0.19222])

alignment.align_measurement_sets(reference_ms       = reference_for_SB_alignment,
                                 align_ms           = offset_SB_EBs,
                                 align_offsets      = alignment_offsets)