ALMA Renormalization Correction 6.6.1

Background

ALMA observations of sources with strong line emission are affected by amplitude calibration issues caused by the ALMA normalization strategy, as described in the following Knowledgebase Articles:

• What are the amplitude calibration issues caused by ALMA's normalization strategy?
• What errors could originate from the correlator spectral normalization and Tsys calibration?

Applying Renorm to Data

If a correction factor of more than 2% is calculated for a dataset, it will be corrected during data reduction for all newly observed datasets. If you have a dataset where this correction has not been applied (this should be indicated in the Pipeline weblog or Manual Data Reduction Script), the following example script will calculate and apply the corrections to the dataset. Modify the vislist parameter with a list of the ASDM(s) to check.

import os
__rethrow_casa_exceptions = True
vislist = ['uid___A002_Xe5aacf_X244e.ms']
for ii in range(1,len(vislist)+1):
    sessionIDs.append(f'session_{ii}')
h_init()
try:
    hifa_importdata(vis=vislist, session=sessionIDs, ocorr_mode='ca')
    hifa_renorm(createcaltable=True, atm_auto_exclude=True) 
    hif_mstransform()
    for vis in vislist:
        targetsVis = vis.split('.')[0] + '_targets.ms'
        applycal(vis=targetsVis,
            gaintable = f'{vis}.hifa_renorm.s2_0.ampcal.tbl',
            intent='OBSERVE_TARGET#ON_SOURCE',
            interp = 'nearest,linear',
            calwt = True)
finally:
    h_save()

This script should be run in the calibrated/working/ directory after you've restored the calibrated data. The resulting uid*_targets.ms file will be corrected if the renormalization factor is >2%. Make sure to use the CORRECTED column. The calculated renormalization factors along with plots can be viewed in the weblog produced by the script. You are encouraged to reach out to the ALMA Helpdesk for assistance in reviewing renormalization plots.

Resources

For more information, please refer to the Pipeline User's Guide.

Version History

• CASA 6.6.1 + Pipeline 2024.1.0.8: The application of renorm was moved from within the hifa_renorm task to hif_applycal.
• CASA 6.4.1 + Pipeline 2022.2.0.64: The parameter atm_auto_exclude is added.
• CASA 6.2.1 + Pipeline 2021.2.0.128: The task hifa_renorm is added.

For CASA versions 6.5.4 and earlier, please see:

• ALMA Renormalization Correction 6.5.4