The Factor directions file

A file defining the direction-dependent calibrators may be provided. The directions files is a simple text file listing various parameters of the direction-dependent calibrators (e.g., position, size, etc.). A typical directions file is shown below:

# This is an example directions file for Factor.
#
# Directions should be sorted in order of reduction (e.g., bright to faint).
#
# Columns are defined as follows:
#
# name position mscale_selfcal_do mscale_facet_do cal_imsize solint_ph solint_amp dynamic_range region_selfcal region_facet peel_skymodel outlier_source cal_size_deg cal_flux_mjy
#
# Values of "empty" (for string or boolean entries) or 0 (for integer entries) indicate
# that they should be derived internally by Factor.

s1  14h41m01.884,+35d30m31.52 empty empty 512  1  30  LD empty empty /full/path/to/s1.skymodel True 0.01 2400
s2  14h38m29.584,+33d57m37.82 True  True    0  1   0  LD empty empty empty False 0.02 1300
s25 14h21m07.482,+35d35m22.87 empty empty   0  2   0  LD empty /full/path/to/s25.rgn empty False 0.1 1020
...

The columns are described below. The calibrators will be processed in the order in which they are given. If a directions file is provided, it must be specified with the directions_file option in the parset. If not, Factor will identify suitable calibrators (or calibrator groups) using the values of the flux_min_for_merging_Jy, size_max_arcmin, separation_max_arcmin, and flux_min_Jy parameters in the parset.

Note

You can let Factor generate the directions file itself and then edit the file to adjust the calibrators by hand. To do this, set interactive to True in the parset so that Factor will pause to allow editing. Once you are done, you can continue the same Factor run and it will pick up any changes made to the file.

Columns

name

The name of the calibrator or facet.

position

The RA and Dec (J2000) of the calibrator, written as RA,Dec in sexagesimal format (note that there should be no space after the comma). If the calibrator is a group of more than one source, this position should define the center of a calibration group.

mscale_selfcal_do

If True, multiscale clean will be used during selfcal with the scales specified by selfcal_multiscale_scales_pixel or auto-selected by WSClean (note that when mscale_selfcal_do = False, multiscale clean is still done for the later stages of selfcal, but only with scales of 0 and 7 pixels). If empty, Factor will activate multiscale clean if it determines that the calibrator has a diameter of 4 arcmin or larger in the facet sky model.

mscale_facet_do

If True, multiscale clean will be used during facet imaging with the scales specified by facet_multiscale_scales_pixel or auto-selected by WSClean. If empty, Factor will activate multiscale clean if it identifies a source with a diameter of 4 arcmin or larger in the facet sky model or if the facet contains the target (specified with the target_ra, target_dec, and target_radius_arcmin parameters).

cal_imsize

The width in pixels of calibrator image. If 0, Factor will determine the width from the size of the calibrator or calibrator group.

solint_ph

The solution interval in seconds for the phase-only solve. If 0, Factor will set the solution interval based on the brightness of the calibrator or calibrator group.

solint_amp

The solution interval in seconds for the amplitude solve. If 0, Factor will set the solution interval based on the brightness of the calibrator or calibrator group.

dynamic_range

If HD, amplitudes are solved for every channel. If LD, amplitudes are solved for every band.

region_selfcal

The region to use as a clean mask during self calibration. If given, this region must cover all emission in the self calibration image that should be cleaned.

region_facet

The region to use as a clean mask during facet imaging. If given, this region must cover all emission in the facet that should be cleaned, unless the automask_facet_image option in the parset is False, in which case this region will be unioned with a PyBDSF-generated one.

peel_skymodel

The sky model to use during peeling (if the outlier_source column is set to True or if the calibrator flux density exceeds that set with the peel_flux_Jy option in the parset).

All sources in the sky model must be grouped into a single patch.

outlier_source

If True, the calibrator will be peeled using the sky model given in the peel_skymodel column and self calibration will not be done.

cal_size_deg

The size (diameter or width) of the calibrator or calibrator group in degrees. This value sets the size of the region used for self calibration and determines which sources are added back for self calibration (so all sources used for self calibration must lie in a region of this size centered on the position given in the position column).

cal_flux_mjy

The total flux density of the calibrator or calibrator group in mJy. This value is not used by Factor but is written by LSMTool for convenience.