INNAME Input UV data (name) INCLASS Input UV data (class) INSEQ Input UV data (seq. #) INDISK Input UV data disk drive # IN2NAME UV work file name IN2CLASS UV work file class IN2SEQ 0.0 0.0 UV work file seq - MUST BE 0 IN2DISK UV work file disk BCHAN 0.0 8192.0 Low freq. channel 0 for cont. ECHAN 0.0 8192.0 Highest freq channel CHANNEL Restart channel number NCHAV Number of chan. to average. CHINC Channel incr. between maps. STOKES Stokes parameters (see HELP) BIF First IF in average. EIF Last IF in average. OUTNAME Output image name (name) OUTDISK Output image disk drive # OUTSEQ -1.0 9999.0 Output seq. no. OUTVER CC ver. no (Continuum only) CELLSIZE 1.E-12 (X,Y) size of grid in asec IMSIZE 0.0 4096. Minimum image size NFIELD 0. 4096. Number of fields (max 4096) FLDSIZE 0. 4096. Size of each field. RASHIFT RA shift per field (asec) DECSHIFT DEC shift per field (asec) NBOXES 0.0 50.0 Number of boxes for CLEAN NB: field 1 only. CLBOX -2.0 4096.0 Four coordinates for each box UVTAPER 0. (U,V) Gaussian taper units are kilo-lambda UVRANGE 0. Min & max baseline (klambda) UVWTFN UV dist. weight function blank => uniform UVBOX 0. 128. Additional rows and columns used in weighting. ZEROSP 0-spacing fluxes and weights XTYPE 0. 10. Conv. function type in x default spheroidal YTYPE 0. 10. Conv. function type in y default spheroidal XPARM Conv. function parms for x YPARM Conv. function parms for y GAIN 0.0 2.0 CLEAN loop gain FLUX Minimum CLEAN component (Jy) MINPATCH 0.0 Min. BEAM half-width in AP. NITER 0.0 Maximum # of CLEAN components BCOMP Begin at BCOMP component Specify for each field. BMAJ -999.9 FWHM(asec) major axis CLEAN restoring beam. BMIN -999.9 FWHM(asec) minor axis CLEAN restoring beam. BPA -360.0 360.0 CLEAN beam position angle PHAT 0.0 999.0 Prussian hat height. FACTOR -5.0 5.0 Speedup factor see HELP CMETHOD Modeling method: 'DFT','GRID',' ' CPARM Task enrichment parameters (1) Antenna diameter (m) (2) Source Spectral index (3) Frequency scaling factor (4) >0 => do DFT imaging (5) >0 => scale residuals (6) Halfwidth in x of beam (7) Halfwidth in y of beam GUARD -1.0 0.9 x,y guard band fractional radius MAXPIXEL 0.0 500000.0 Maximum pixels searched in each major cycle. BADDISK -1.0 1000.0 Disks to avoid for scratch. BOXFILE Input file for clean boxes ' ' => use NBOXES, CLBOX

WFCLN Type: Task Use: Wide field imaging/CLEANing task. WFCLN has been replaced by IMAGR for all uses. WFCLN does a visibility base CLEAN similar to MX but offers a variety of corrections related to imaging wide fields and/or multi or wideband frequency observations. These are: 1) Relative frequency dependent primary beam corrections in the CLEAN subtractions from the visibility data. 2) Simple correction for source spectral index. 3) Correct errors in assumed center frequency. 4) Uses double size beam if possible for CLEANs. 5) Labels images with average zenith and parallactic angles so that snapshot VLA images can be corrected with OHGEO for misaligned coplanar array geometric distortion. 6) Supports 3-D DFT imaging to avoid noncoplanar array image distortion. (THIS IS REALLY SLOW!) 7) After CLEANing the residuals may be scaled by the ratio of the restoring beam area to the dirty beam area. CPARM(5) > 0 enables this option. The dirty beam area is determined in a box centered on the peak of half width CPARM(6) in x (RA) and CPARM(7) in y (dec). Adverbs: INNAME.....Input UV data file (name). Standard defaults. INCLASS....Input UV data file (class). Standard defaults. INSEQ......Input UV data file (seq. #). 0 => highest. INDISK.....Input UV data file disk drive #. 0 => any. IN2NAME....UV data work file name. This file is used as the scratch file and may be used when restarting WFCLN or to examine the final residuals. Default=OUTNAME. RESTARTING WITH A PRE-EXISTING FILE APPEARS NEVER TO BE QUICK IN WFCLN AND IS REPORTED TO CAUSE THE TASK TO FAIL SOMETIMES. THEREFORE, YOU WILL ALWAYS BE GIVEN A NEW WORK FILE. IN2CLASS...UV work file class. Default='WFCLN' IN2SEQ.....UV work data file sequence number. <= 0 => highest existing + 1. IN2SEQ IS FORCED TO BE 0 TO CREATE A NEW WORK FILE EVERY TIME. (See above) IN2DISK....UV work data file disk number. BCHAN......First channel number to image, 0=>1. Channel numbers are 1 relative as defined in the input data file. ECHAN......Highest channel number to to include in image, 0=>MAX The actual # of output channels will be (BCHAN-ECHAN+1-NCHAV)/CHINC + 1 Thus, ECHAN is the highest channel in the input averaged into the output. There is a limit of 46655 channels. CHANNEL....To restart a map/CLEAN with a given frequency channel, specify that (input) channel in CHANNEL NCHAV......NCHAV is the number of channels to be averaged together in in the gridding process. 0 => 1. If this value is less than the total number of channels, then a multi-channel image will result. CHINC......Number of input channels to skip between images. 0 => 1 STOKES.....Make images with this STOKES parameter. Unlike UVMAP only one STOKES is permitted per execution. (A beam is made for each frequency channel) 'I', 'Q','U', 'V', 'R' (=RCP), 'L' (=LCP) BIF........The lowest numbered IF to include. Multiple IFs can be included in a bandwidth synthesis average. 0 => 1. EIF........The highest numbered IF to include. 0 =>highest. Note: not all data sets will have IFs. OUTNAME....Output image name (name). Standard defaults. OUTDISK....The disk drive # of output images. 0 => highest with space (note: map and Beam go on same disk. Note: OUTCLASS='xCLnnn' where x=Stokes, nnn=field number and 'xBM001' is the beam CLASS. If NITER=0, OUTCLASS='xIMnnn' OUTSEQ.....Output sequence number. Note: All maps and beam have same sequence number. 0 => highest to produce unique maps and beam. OUTVER.....CC table version number for continuum data only. For line data the channel number is used for the version number. CELLSIZE...(X,Y) pixel separation in asec. IMSIZE.....(X,Y) The minimum desired size of the fields, regardless of the FLDSIZE for component search. NFIELD.....The number of fields to map in the antenna beam. Up to 4096 are allowed but should be non overlapping. FLDSIZE....(X,Y) field size in pixels for the component search during cleaning; one per field. Should be in the range 32X32 to 4096X4096. Output image size will be increased to the next highest power of two, but only the region specified will be searched for components. Default is IMSIZE-10 RASHIFT....RA shift of the phase center of each field from the tangent point of the uv data in asec. Map center = tangent point + shift. If X>0 shifts map center to east. NOTE: RASHIFT is a shift in RA scaled by cos (Dec_0) as Ra_new = RA_0 + RASHIFT/cos (Dec_0) where _0 => the tangent point in the uv data. If the UV data have been rotated then RASHIFT and DECSHIFT refer to X and Y in the new coordinate system. The DO3DIMAG option in IMAGR is not supported by WFCLN. DECSHIFT...Declination shift of map center from tangent point of each field in asec. Map center = tangent point + shift. If Y>0 shifts map center to north. NBOXES.....Number (<=50) of rectangular search boxes to search on the first field; the clean window in all other fields is given by FLDSIZE. 0 => use FLDSIZE to determine windows on field 1. CLBOX......A 4x50 array with the BLC and TRC of each box. 0 => use window specified in FLDSIZE. CLBOX(1,i)=-1 indicates a circle of radius CLBOX(2,i) pixels centered on (CLBOX(3,i), CLBOX(4,i)). CLBOX(1,i) >= 0 indicates a rectangular box. NOTE: CLBOX is not used to determine the size of the image to be made; IMSIZE or FLDSIZE must set the size of the image. UVTAPER....(U,V) Gaussian taper (kilo-lambda) at 30 percent level UVRANGE....(Minimum,Maximum) baseline (kilo-lambda) in map. UVWTFN.....Weighting function of (u-v) place. blank=>Uniform; 'NA'=>Natural 'O '=> Set weights to One and do uniform weighting. 'V '=>VLBI weighting, forth root of input weight, and do uniform weighting. 'NO'=>Set weights to one and use natural weighting. 'NV'=>VLBI weight and use natural weighting. Note: uniform weighting in WFCLN corrects by the sum of the weights in the box rather than the number of visibilities as in MX. UVBOX......(U,V) box size for smoothing. See HELP UVBOX. ZEROSP.....(1)= zero spacing flux density for the polarization being processed. Zero spacing flux is placed at the center of FIELD 1. (2)= FWHM size of major axis for Zero spacing flux component (in arc seconds). (3)= FWHM size of minor axis for Zero spacing flux (4)= Position angle (north through east, degrees) If (2) is zero, source is assumed bigger than image. ZEROSP(5) is the weight for zero spacing flux. XTYPE......Convolution function type in X-direction 1=Pill-box, 2=exponential, 3=Sinc, 4=Exp*Sinc, 5=Spheroidal, 6=exp*BESSJ1(x)/x. <= 0 or > 5 -> 5. YTYPE.....Convolution function type in Y-direction XPARM.....Array containing parameters for XTYPE. See HELP UVnTYPE when n=convolution type. YPARM.....Array containing parameters for YTYPE. GAIN......The CLEAN loop gain. 0 => 0.10. FLUX......Stop CLEAN when abs(resid. image max) < FLUX (Jy) IF FLUX < 0 then Clean stops at first negative Clean Component. MINPATCH..Minimum half width of the portion of the beam which is used in the AP minor CLEAN. (init 51) Use 51 for deep CLEANs of extended sources. Use a large value if the beam has big side-lobes. NITER.....CLEAN iteration limit. 0 => no CLEANing. BCOMP.....Restart CLEAN using BCOMP(i) components for each field i. If >0, you must completely specify the OUTNAME and OUTSEQ of the clean map(s). BMAJ......The FWHM (asec) major axis of the restoring beam. If 0; value obtained from fitting to the beam. If <0; output will contain the residual image. BMIN......The FWHM (asec) minor axis of the restoring beam. BPA.......The position angle in the unrotated image of BMAJ. PHAT......The offset added to the pixel at the beam peak. Should be about/2* but you may well need to experiment. FACTOR....FACTOR>0 causes deeper CLEAN in each major cycle, speeding CLEAN, maybe "eating" extended structure. FACTOR=0 => the normal Clark CLEAN. FACTOR=-0.3 is good for deep CLEANs of extended structure. CMETHOD...This determines the method used to compute the model visibility values. 'DFT' uses the direct Fourier transform, this method is the most accurate. 'GRID' does a gridded-FFT interpolation model computation. ' ' allows the program to use the fastest method. CPARM.....Correction control parameters (SEE EXPLAIN WFCLN): (1) If > 0 then make frequency dependent primary beam corrections assuming an antenna diameter of CPARM(1) meters. (2) Visibility amplitudes will be corrected to the average frequency assuming a spectral index of CPARM(2). Note: the typical optically thin synchrotron spectral index is about -0.7. (3) If this value is larger than 0 then the u,v and w terms are scaled by CPARM(3) before imaging. (4) If this value is larger than 0 then use a DFT onto the celestial sphere. THIS IS VERY SLOW. (5-7) If (5) > 0 then scaling od residuals is requested and CPARM(6) = Halfwidth in x of box to determine the dirty beam area (default = 5) CPARM(7) = Halfwidth in y of box to determine the dirty beam area (default = 5) GUARD.....Fraction of the x and y radius for which uv samples are not allowed. < 0 => just enough to avoid mathematical errors in the convolution. 0 => 0.3 * SQRT(taper weight at 0.3 from edge). MAXPIXEL..The maximum number of pixels that are searched for components inside the ``AP'' in each major cycle. < 3000 => 20050. This number affects the cpu usage significantly. Too many causes the task to search over many points it will never use. Too few causes the task to do many more small major cycles, also at great expense. Use this with great caution, but big wins are possible using larger sizes on very large cleans. BADDISK...This array contains the numbers of disks on which it is desired that scratch files not be located. BADDISK has no effect on input and output maps. BOXFILE...Input file of clean box definitions . This is a text file containing the coordinates of clean boxes for all fields. The format is one box per line, as follows: field blc-x blc-y trc-x trc-y (5 integers) e.g. 1 200 205 220 222 1 230 232 240 241 2 100 100 130 121 ... Fields with no boxes specified default to the size specified by IMSIZE and FLDSIZ (see above). Use of this input overrides all other clean box information. E.g. BOXFILE 'FITS:BOXES' If BOXFILE = ' ', NBOXES and CLBOX apply.

WFCLN: Widefield or wideband imaging/CLEANing task. Documentor: W. D. Cotton, NRAO Related Programs: MX, OHGEO, UBAVG This task does a visibility based CLEAN similar to MX but contains a number of optional corrections and enhancements which are useful for imaging a wide field of view and/or using multiple or wide frequency bands. Frequency Dependent Primary beam corrections: If multiple, widely spaced frequencies are used in a making a single image then the differences in the primary beam size can vary signifigantly with frequency. This causes problem in CLEANing objects far from the pointing center as the primary beam differences cause the subtraction of the combined model from the visibility data at the different frequencies to be incorrect. There will be residuals in the visibility data that cannot be CLEANed as the data does not correspond to a possible sky brightness distribution. If CPARM(1) is larger than 0 then a correction is made in the subtraction to remove the effects of the frequency dependence of the primary beam. The primary beam is assumed to be a uniformly illuminated disk of diameter CPARM(1) meters. This correction is made out to the 5 percent power point of the beam with a flat correction further out. Note: this correction is only for the relative primary beam to correct to a common frequency and DOES NOT correct for the primary beam pattern at this frequency. Simple Correction for Spectral Index: If the sources observed do not have a flat spectrum then the source spectrum will have effects on the CLEANing of a similar nature to the frequency dependent primary beam problem described above. This problem does not depend on position in the field except in the the spectral index can vary across the field. In general the spectral index does vary in an image but in many cases the spectral index is usually closer to -.7 than to 0. To the degree that the structure in the field can be characterized by a single spectral index the amplitudes of the data can be scaled to the average frequency. Before imaging the amplitudes of the uv data are scaled to the average frequency using a spectral index of CPARM(2). For optically thin synchrotron sources this spectral index is typically between -0.6 and -1.0. This correction cannot remove the effects of variable spectral index but allows a single correction. Error in the Assumed Central Frequency: If the frequency used to compute the u, v a, w terms is in error then there will be a misscaling of the image due to this error. Central frequencies are frequently computed on the basis of unrealistic models of the bandpass shape. If CPARM(3) is larger than 0 it is assumed to be a frequency scaling factor for the u, v, and w that is to be applied before imaging. Array Misorientation Effects Images made with a coplanar array not oriented towards the instrumental zenith will have a distortion of the geometry which increases in severity away from the phase tracking center. For noncoplanar arrays the image is distorted rather than just the geometry. VLA snapshots are misaligned coplanar arrays whereas VLA synthesis images cannot be considered to be made with a coplanar array. Images made with misaligned coplanar arrays can be corrected using task OHGEO to remove the effects of this misalignment. This correction requires the knowledge of the observing geometry; in particular, the average parallactic and zenith angles. WFCLN computes these values and leaves then as header keywords where OHGEO can use them. Noncoplanar Effects If the observing array is not confined to a plane during the observations then images produced from a 2-D FFT will be increasing distorted from the phase center. If this is a serious problem then using a direct Fourier transform (DFT) to image onto the celestial sphere can eliminate this problem. However, THIS IS VERY SSSLLLOOOWWW. In addition, the dirty beam is no longer a stationary function of position in the field and a very conservative visibility based CLEAN is needed making this EVEN SLOWER. If CPARM(4) is greater than 0 then imaging and model subtraction will be done using a DFT. Be prepared to wait. There is also a limit of 1 field in this mode. There are several other changes in the cleaning for this mode; especially, the beam patch used is fixed at a small value. Since the speed of the DFT imaging is directly proportional to the number of visibilities time averaging is advised. Task UBAVG can be used to time average to the maximum possible extent without distorting a specified field of view. Scaling residuals In general the units of the residuals are different than those of the restored components; either being Jy per beam area. If the dirty beam area is similar to the restoring beam area then this effect is negliglible. Similarly, if the CLEAN has proceeded well into the noise then this difference is of little consequence. However, if there is signifigant unCLEANed flux left in the image then this difference may be important. If CPARM(5) > 0 then WFCLN will attempt to scale the residuals to the same units as the restored components. The principle difficulty is determining the effective area of the dirty beam. Operationally this is done inside a box centered on the peak in the beam with halfwidth CPARM(6) in x and CPARM(7) in y.