Tracking moving sources or sources with ephemeris tables

if the phasecenter is the name known major solar system object ('MERCURY', 'VENUS', 'MARS', 'JUPITER', 'SATURN', 'URANUS', 'NEPTUNE', 'PLUTO', 'SUN', 'MOON') or is an ephemerides table then that source is tracked and the background sources get smeared (especially for long observations or multi epoch data).

There is a special case, when phasecenter='TRACKFIELD', which will use the ephemerides or polynomial phasecenter in the FIELD table of the MS's as the source center to track.

When in tracking mode  the image center will be the direction of the source at the first time in the user selected data. All other time the source will be shifted by the amount it has moved in the frame of the image to that initial time.


E.g of usage with an ephemeride table in casa format is


This is when you have an ephermeris table that cover the whole observation you can do it like this

tclean(vis=['', '', '', '', ''],selectdata=True,field="DES_DEEDEE",spw=['17,19,21,23', '17,19,21,23', '17,19,21,23', '17,19,21,23', '17,19,21,23'],intent="OBSERVE_TARGET#ON_SOURCE",datacolumn="data",imagename="test_track",imsize=[2000, 2000],cell=['0.037arcsec'],phasecenter="",stokes="I")


 You can check if the ephermeris table is of the format that casa accepts by using the measures tool framecomet function.


if it accepts without complaining then it should work in tclean


If the source you are tracking is one of the 10 that casa measures has the ephemerides from the JPL DE200 or DE405 then you can use their names directly as such

tclean(vis=['', '', '', ''],selectdata=True,field="Jupiter",spw=['17,19,21,23', '17,19,21,23', '17,19,21,23', '17,19,21,23'],intent="OBSERVE_TARGET#ON_SOURCE",datacolumn="corrected",imagename="alltogether",imsize=[700, 700],cell=['0.16arcsec'],phasecenter="JUPITER",stokes="I")


For ALMA data mainly the correlator may have the ephemerides of a moving source already attached to the FIELD tables of the MeasurementSets as it was used to phase track the source. In such special case you can use the keyword "TRACKFIELD" in the phasecenter parameter, then the internal ephemerides will be used to track the source.

tclean(vis=['', '', '', '', ''],selectdata=True,field="DES_DEEDEE",spw=['17,19,21,23', '17,19,21,23', '17,19,21,23', '17,19,21,23', '17,19,21,23'],intent="OBSERVE_TARGET#ON_SOURCE",datacolumn="data",imagename="test_track",imsize=[2000, 2000],cell=['0.037arcsec'],phasecenter="TRACKFIELD",stokes="I")