Description

 

ALERT: uvcontsub3 is an experimental task and will eventually replace the current uvcontsub code with the goal of taking less time and temporary disk space.

 

 

uvcontsub3 is a task to perform continuum fitting and subtraction in the uv plane
 
This task estimates the continuum emission by fitting polynomials to the real and imaginary parts of the spectral windows and channels selected by fitspw. This fit represents a model of the continuum in all channels. The fitted continuum spectrum is subtracted from all channels selected in spw, and the result (presumably only line emission) is stored in a new MS that is always called vis + ".contsub". If an MS with the output name already exists, it will be overwritten.
 
uvcontsub3 will read from the CORRECTED_DATA column of vis if it is present, or DATA if it is not. Whichever column is read is presumed to have already been calibrated.
  
WARNING: Strictly speaking, the uvcontsub3 model is only a good representation of the continuum at the phase center. Residuals may be visible for sources far away and one may try imcontsub in the image domain for improved results. 

WARNING: fitorders > 1 are strongly discouraged because high order polynomials have more flexibility, may absorb line emission, and tend to go wild at the edges of fitspw, which is not what you want. default: 0 (constant)

 
 

Parameter descriptions

vis

Name of input MS. Output goes to vis + ".contsub" (will be overwritten if already exists)

fitspw  

Selection of spectral windows and channels to use in the fit for the continuum, using general MS selection syntax for spectral windows, e.g. in spw:chan format (spw ids are required but '*' can be used) or as frequencies. See the note under combine. default: fitspw=''  (all)

WARNING: The fitspw selection is based on the channel numbers in the uv-data of the input MS file, which are most likely different from the channel numbers in the image plane after running tclean. 

combine

Continuum solutions will break at scan, field, and spw boundaries according to solint. To allow solutions across these boundaries, combine can be set to 'spw', 'scan', or 'spw, scan'.  combine must include 'spw'  if spw contains spws that are not in fitspw!  default: ''  which is that solutions will break at scan, field, and spw

fitorder

Polynomial order for the fits of the continuum w.r.t. frequency. fitorders > 1 are strongly discouraged because high order polynomials have more flexibility, may
absorb line emission, and tend to go wild at the edges of fitspw, which is not what you want. default: 0 (constant)

field

Field selection for continuum estimation and subtraction. The estimation and subtraction is done for each selected field separately in turn. default: ''  (all fields). (See Data Selection in a MeasurementSet)

spw

Optional per spectral window selection of channels to include in the output. See the note under combine. The sub-MS output spectral windows will be renumbered to start from 0, as in split. default: '' (all spws)   (See Data Selection in a MeasurementSet)

scan

Scan id selection. default: '' (all scans) (See Data Selection in a MeasurementSet)

intent

Selection by scan intent. default: '' (all intents)  (See Data Selection in a MeasurementSet)

correlation

Selection by correlation. default: '' (all correlations)  (polarization products)  (See Data Selection in a MeasurementSet)

observation

Selection by observation id. default: '' (all obs ids)  (See Data Selection in a MeasurementSet)