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NRAO Home > CASA > CASA Task Reference Manual |
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0.1.134 uvcontsub
Requires:
Synopsis
Continuum fitting and subtraction in the uv plane
Description
Arguments
Inputs |
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vis |
| Name of input MS. Output goes to vis + ”.contsub”
(will be overwritten if already exists)
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| allowed: | string |
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| Default: |
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field |
| Select field(s) using id(s) or name(s)
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| allowed: | any |
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| Default: | variant
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fitspw |
| Spectral window:channel selection for fitting the
continuum | |
| allowed: | string |
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| Default: |
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excludechans |
| exclude Spectral window:channel selection in fitspw for
fitting
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| allowed: | bool |
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| Default: | False |
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combine |
| Data axes to combine for the continuum estimation
(none, or spw and/or scan)
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| allowed: | string |
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| Default: |
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solint |
| Continuum fit timescale (int recommended!)
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| allowed: | any |
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| Default: | variant int |
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fitorder |
| Polynomial order for the fits
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| allowed: | int |
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| Default: | 0 |
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spw |
| Spectral window selection for output
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| allowed: | string |
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| Default: |
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want_cont |
| Create vis + ”.cont” to hold the continuum estimate.
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| allowed: | bool |
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| Default: | False |
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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 (vis + ".contsub"). If an MS
with the output name already exists, it will be overwritten.
It 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.
If want_cont is True, the continuum fit is placed in a second new MS
(vis + ’.cont’, also overwritten if it already exists).
N.B. because the continuum model is necessarily a
smoothed fit, images made with it are liable to have their field of
view reduced in some strange way. Images of the continuum should be
made by simply excluding the line channels (and probably averaging the
remaining ones) in clean.
Keyword arguments:
vis -- Name of input visibility file
default: none; example: vis=’ngc5921.ms’
field -- Field selection for continuum estimation and subtraction.
The estimation and subtraction is done for each selected field
in turn. (Run listobs to get lists of the ID and names.)
default: field = ’’ means select all fields
field = 1 # will get field_id=1 (if you give it an
integer, it will retrieve the source with that index.
field = ’1328+307’ specifies source ’1328+307’
field = ’13*’ will retrieve ’1328+307’ and any other fields
beginning with ’13’
fitspw -- Selection of spectral windows and channels to use in the
fit for the continuum, using general spw:chan syntax.
The ranges of channels also can be specified by frequencies as in
the MS selection syntax (spw ids are required but ’*’ can be
used, see the example below).
See the note under combine.
default: ’’ (all)
example: fitspw=’0:5~30;40~55’
--> select the ranges by channels in the spw id 0
fitspw=’0:5~30;40~55,1:10~25;45~58,2’
--> select channel ranges 5-30 and 40-55 for the spw id 0,
10-25 and 45-58 for spwid 1, and use all channels for the spw id 2
fitspw=’0:113.767~114.528GHz;114.744~115.447GHz’
--> select the ranges by frequencies in the spw id 0
fitspw=’0:113.767~114.528GHz;114.744~115.447GHz,1:111.892~112.654GHz;112.868~113.025GHz’
--> select the different ranges by frequencies for the spw ids 0 and 1
fitspw=’*:113.767~114.528GHz;114.744~115.447GHz’
--> select the same frequency ranges for all the relevant spws
>>> expandable parameter for fitspw
excludechans - if True, it will exclude the spws:channels specified in fitspw
for the fit
default: False (use fitspw for the fit)
example: fitspw=’0:114.528GHz~114.744GHz’; excludechans=True
--> exclude the frequency range, 114.528GHz - 114.744GHz in the spw id 0
combine -- Data axes to combine for the continuum estimate.
It must include ’spw’ if spw contains spws that are not in
fitspw!
default: ’’ --> solutions will break at scan, field, and spw
boundaries according to solint
Options: ’’, ’spw’’, ’scan’, or ’spw, scan’
example: combine=’spw’ --> form spw-merged continuum estimate
solint -- Timescale for per-baseline fit (units optional)
default (recommended): ’int’ --> no time averaging, do a
fit for each integration and let the
noisy fits average out in the image.
example: solint=’10s’ --> average to 10s before fitting
10 or ’10’ --> ’10s’ (unitless: assumes seconds)
options: ’int’ --> per integration
’inf’ --> per scan
If solint is longer than ’int’, the continuum estimate can be
corrupted by time smearing!
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 go wild at the edges of
fitspw, which is not what you want.
default: 0 (constant); example: fitorder=1
spw -- Optional per spectral window selection of channels to include
in the output. See the note under combine.
The spectral windows will be renumbered to start from 0, as in
split.
want_cont -- Create vis + ’.cont’ to hold the continuum estimate.
default: ’False’; example: want_cont=True
The continuum estimate will be placed in vis + ’.cont’
async -- Run task in a separate process (return CASA prompt)
default: False; example: async=True
More information about CASA may be found at the
CASA web page
Copyright © 2016 Associated Universities Inc., Washington, D.C.
This code is available under the terms of the GNU General Public Lincense
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