ms.continuumsub - Function

Continuum fitting and subtraction in uv plane

Synopsis
continuumsub(fldid, spwid, chans, solint, fitorder, mode)

Arguments

fldid	in	Desired fields to fit
		Allowed:	Vector of integers
		Default:	no default
spwid	in	Desired spectral windows to fit
		Allowed:	Vector of integers
		Default:	all
chans	in	Range of channels to fit
		Allowed:	Vector of integers
		Default:	all
solint	in	Averaging time (s)
		Allowed:	Float
		Default:	0.0 (scans)
fitorder	in	Polynomial order for fit
		Allowed:	Integer
		Default:	0
mode	in	Desired use of fit model (see below)
		Allowed:	String
		Default:	'subtract'

Description
This function does exactly the same as uvlsf, and will replace that function in future when it proves to be sufficiently bug free. Continuumsub is written in C++ as opposed to glish and is faster by a factor 3-10 (depends on size of dataset and solution interval). This function provides a means of continuum determination and subtraction by fitting a polynomial of desired order to a subset of channels in each time-averaged uv spectrum. The fit is used to model the continuum in all channels (not just those used in the fit), for subtraction, if desired. Use the chans parameter to limit the range of channels used to estimate the continuum (avoid channels containing spectral lines). The default solution interval (0.0s) will average the data over scans (per-baseline) before doing the fit. The mode parameter indicates how the continuum model (the result of the fit) should be used: 'subtract' will store the continuum model in the MODEL_DATA column and subtract it from the CORRECTED_DATA column; 'replace' will replace the CORRECTED_DATA column with the continuum model (useful if you want to image the continuum model result); and 'model' will only store the continuum model in the MODEL_DATA column (the CORRECTED_DATA is unaffected).

It is important to start the ms tool with readonly=F so that changes to the dataset will be allowed (see example below).

For now, the only way to recover the un-subtracted CORRECTED_DATA column is to use calibrater.correct() again.

Note that the MODEL_DATA and CORRECTED_DATA columns must be present for continuumsub to work correctly. The function will warn the user if they are not present, and abort. To add these scratch columns (for now), done the ms tool, then start a calibrater or an imager tool, which will add the scratch columns. Then restart the ms tool, and try continuumsub again.

Options for shifting known bright sources to the phase center and for editing based on the rms fit will be added in the near future.

Example

      include 'ms.g'
      myms := ms('ngc5921.ms',readonly=F);    # writable!
      myms.continuumsub(fldid=3,spwid=1,chans=[5:9,50:59],
                 solint=0.0,fitorder=1,mode='sub');
      myms.done();

This example will fit a line to channels 5-9 and 50-59 in spectral window 1 in each scan-averaged spectrum for field 3, and store the result in the MODEL_DATA column and subtract it from the CORRECTED_DATA column.

Next: ms.uvlsf - Function Up: ms - Tool Previous: ms.clearbuffer - Function Contents Index

	Package	general
	Module	ms
	Tool	ms