AIPS HELP file for SETFC in 31DEC24
As of Fri Apr 26 2:21:58 2024
SETFC: Task to make a BOXFILE for input to IMAGR
INPUTS
INNAME UV dataset name (name)
INCLASS UV dataset name (class)
INSEQ 0.0 9999.0 UV dataset name (seq. #)
INDISK 0.0 9.0 Disk drive #
SRCNAME Source selected
BCOUNT 0.0 511.0 First field number to use
BOXFILE
disk file to write to (the
input BOXFILE for IMAGR)
CELLSIZE $ 0.0 (X,Y) size of grid in asec
IMSIZE $ 0.0 16384 field size
SHIFT Position shift (RA,Dec) asec
for all fields
FLUX Minimum component flux =
(source * beam)
BPARM (1) Inner region radius (deg)
(2) Field overlap (pixels)
(3) Factor to scale NVSS
fluxes, 0 -> 1
(4) Radius NVSS search (deg)
(5) Flux limit in NVSS (Jy)
(6) IMSIZE for NVSS fields
(7) IMSIZE for Sun fields
(8) Write Clean boxes for
NVSS fields
(9) Maximum allowed phase
error in imaging
(10) Points per beam
OPTYPE 'USEF' -> use F type field
cards rather than C type
PBPARM Beam parameters:
(1) Cutoff; (2) Use (3)-(7)
(3)-(7) Beam shape parms
INLIST
NVSS input file name
' ' => AIPS provided.
NFIELD @ Number fields found
HELP SECTION
SETFC
Type: Task
Use: SETFC makes an output BOXFILE to be used as input to IMAGR. It
is meant to be used in preparation for wide-field 3D imaging.
It prepares BOXFILE data to image an area around the pointing
position using a number of overlapped fields. Optionally, it
also searches through lists of sources from the NVSS (21 cm VLA
D-array) or WENSS/WISH (92 cm Westerbork northern and southern)
surveys and adds outlier fields to image those sources above a
specified flux limit. It writes an inscribed circular Clean
box for the fields covering the primary beam and can,
optionally, write small Clean boxes for each of the sources in
the outlier fields. The latter will almost certainly require
later hand editing but they are instructive.
NOTE: if you do not need the BOXFILE, the task will use a blank
BOXFILE as indication that the BOXFILE output should go to the
message terminal instead.
Input adverbs:
INNAME......The UV dataset name (name). Standard defaults.
INCLASS.....The UV dataset name (class). Standard defaults.
INSEQ.......The UV dataset name (seq. #). 0 => highest.
INDISK......The disk drive #. 0 => any.
SRCNAME.....The source to be used from a multi-source file; a single
source name is required to get the central pointing
position from the source table. Ignored for single-source
files.
BCOUNT......First field number to use. 0 -> 1. This allows you to
append to a pre-existing file with lower field numbers
obtained in some other way.
BOXFILE.....Output text file containing lines which specify the fields
for the multi-field imaging. This file should then be
specified as the BOXFILE for IMAGR. If the file already
exists, the new information will be appended to it.
If BOXFILE = ' ', the output will be redirected to the
message terminal/file. The field cards will be at
message level 4, the clean box cards at message level 2.
CELLSIZE....Pixel size for the fields in IMAGR in arc seconds.
Value used is returned (i.e. 0's are changed to
recommended values)
IMSIZE......Size of each field. Value used is returned (i.e. 0's
are changed to recommended values)
If CELLSIZE and/or IMSIZE are zero, the data are read to
find the maximum baseline and maximum W in order to
estimate these parameters. The "maximum phase error" in
gridding ignoring the W term may be controlled with
BPARM(9).
SHIFT.......Specifies a position shift in arc seconds at the phase
center for all of the fields in the inner portion. The
output RA = RA0 + SHIFT(1)/cos(DEC0) and DEC = DEC0 +
SHIFT(2) where 0 refers to the input coordinates.
FLUX........Minimum included component "flux" = source flux times
the single-dish beam power. 0 => any in INLIST meeting
BPARM(4). Note, the single dish beam power is taken to
be 0.01 outside the main lobe. Fluxes are read from the
table, scaled by BPARM(3), and then compared to FLUX.
BPARM.......(1) The radius in degrees to be covered fully by
overlapping fields. <= 0 means do not do fly's eye
list of fields. < 0 => do not include catalog sources
within abs (BPARM(1)) of the origin.
(2) Field overlap in pixels 0 -> 5. The program now
takes into account that the Cleaning area is smaller
than the image size since the outer 6 pixels are
regarded as unreliable.
(3) Factor to scale NVSS fluxes (to account for spectral
index on average). 0 -> 1
(4) Radius for the search in the catalog for interfering
sources. < BPARM(1) => no search. Try 30 for 74
Mhz imaging. All sources outside the center of the
outermost fly's eye field (n.b. < BPARM(1)) and
< BPARM(4) are included if they meet the flux
criteria.
(5) Flux (Jy) limit in catalog search, There are 4
AIPS-provided NVSS files each containing sources > its
flux limit. Those limits are 50, 100, 300, and 1000
mJy and searches will be faster if you are just above
rather than just below one of these limits.
(6) Desired size of external fields; 0 -> 128.
(7) Desired size of external fields on Sun; 0 -> 256.
(8) > 0 => write Clean boxes in outlier fields. If > 5,
use BPARM(8) for the radius in cells.
(9) The phase error made in gridding a point is approx
180 * W * (l*l + m*m) degrees where W is in
wavelengths and l and m in radians. Thus the
maximum field of view (radius) is
sqrt(E/(180*Wmax)).
BPARM(9) gives the allowed value of E in degrees,
where BPARM(9) = 0 -> 45 degrees. The actual value
of E used will be reduced by the cos (zenith angle)
and will be reduced still further if the average
abs(W) > Wmax/4 or the sqrt (average W*W) > Wmax/3.
(10) The cell size recommended is 1 / Bmax / Nppb where
Bmax is tha maximum baseline and Nppb is the number
of points per beam. Even with uniform weighting the
beam is often larger than 1/Bmax so one may end up
with more than Nppb points per beam. BPARM(10) sets
points per beam (when CELLSIZE=0) and 0 -> 3.
OPTYPE......'USEF' -> use F type field cards giving the RAshift and
DECshift of the center of the field (facet)
This can be used for more than one pointing
although the NVSS sources and Sun will not be
correct.
other -> use C type field cards giving the center RA
and DEC for each field
PBPARM......Primary beam parameters:
(1) Lowest beam value to believe: No default.
0.0 => use any beam value
(2) > 0 => Use beam parameters from PBPARM(3)-PBPARM(7)
Otherwise use default parameters for the VLA (or
ATCA where appropriate)
(3-7)..For all wavelengths, the beam is described by the
function:
1.0 + X*PBPARM(3)/(10**3) + X*X*PBPARM(4)/(10**7) +
X*X*X*PBPARM(5)/(10**10) + X*X*X*X*PBPARM(6)/(10**13)
X*X*X*X*X*PBPARM(7)/(10**16)
where X is (distance from the pointing position in arc
minutes times the frequency in GHz)**2.
See explain for details
INLIST......Catalog input file name. For format see Explain
' ' => an AIPS-provided files appropriate to BPARM(5):
Epoch 2000:
FLUX >= 1.000 NV00.1000 ( 2267 objects)
FLUX >= 0.300 NV00.0300 ( 14456 objects)
FLUX >= 0.100 NV00.0100 ( 63411 objects)
FLUX >= 0.030 NV00.0030 (237600 objects)
Epoch 1950:
FLUX >= 1.000 NV50.1000 ( 2267 objects)
FLUX >= 0.300 NV50.0300 ( 14456 objects)
FLUX >= 0.100 NV50.0100 ( 63411 objects)
FLUX >= 0.030 NV50.0030 (237600 objects)
The WENSS/WISH surveys ar also available $AIPSTARS as
FLUX >= 0.100 WE00.0100 ( 99709 object 2000)
FLUX >= 0.100 WE50.0100 ( 99709 object 1950)
Some sites may choose to download really large source
lists to deeper flux levels. These may include from the
NVSS survey:
FLUX >= 0.003 NV00.0003 (1560007 objects, 2000)
FLUX >= 0.003 NV50.0003 (1560007 objects, 1950)
and the WENSS/WISH survey:
FLUX >~ 0.010 WE00.0000 (319770 objects, 2000)
FLUX >~ 0.010 WE50.0000 (319770 objects, 1950)
These deep files may be particularly useful for BOXES
but are too deep to be of much use here.
Note: the WENSS survey covers +90 to +28 degrees
declination and the WISH survey covers -25 to -15 with
some sources to -9.
Output adverbs (returned to AIPS):
CELLSIZE....Pixel size for the fields in IMAGR in arc seconds.
Value used is returned (i.e. 0's are changed to
recommended values)
IMSIZE......Size of each field. Value used is returned (i.e. 0's
are changed to recommended values)
NFIELD......Number of fields put in the bOXFILE.
EXPLAIN SECTION
SETFC: Task to make an input BOXFILE to be used with IMAGR
DOCUMENTOR: Bryan Butler (NRAO)
DESCRIPTION
This task was motivated by Lazio & Kassim's SETFAC RUN file which sets
facets for wide-field imaging via IMAGR. The original version of the
task was then written by Bryan Butler.
The purpose of the task is to set up a BOXFILE for input to IMAGR. This
is intended to be used for wide-field imaging applications (e.g., VLA 74
MHz data), as a way of specifying multiple fields which cover a wide
field of view. It is quite usefull at any wavelength however.
The task, if instructed to determine cell and/or image size, will read
the UV data to find the maximum baseline and maximum W. The cell size
in radians is then 1/Bmax / Nppb where Nppb is the number of points
per beam. The formula for phase error which determines the maximum
radius of a facet comes from Thompson, Moran, and Swenson,
"Interferometry and Synthesis in Radio Astronomy" 2001, pages 73-74.
In radians, the facet radius for which all phase errors are less than
E degrees is sqrt (E / Wmax / 180).
It is found that an error as great as 45 degrees is okay if there are
not too many points at large W and if the elevation is not too low.
The user may control E with BPARM(9) but the E actually used is set
by E = BPARM(9) * cos (ZA) * Wmax / max (Wmax, 4*Wa, 3*Wr)
where ZA is the zenith angle at transit, Wa is the average abs(W),
and Wr = sqrt (average W*W). This biases things when more than a few
points are at large W and reduces the allowed error at low elevations
where the results of the phase errors are more serious.
The task is split into 2 relatively independent parts. The first is the
creation of a "fly's eye" - a tiling of overlapping fields which cover
the central part of the primary beam. The second part is the creation
of several smaller fields which are centered on NVSS sources and the
Sun. The two parts are independent, i.e., you can do either or both of
them on any particular run of SETFC.
The fly's eye tiling is controlled by the parameters BPARM(1), BPARM(2),
CELLSIZE, IMSIZE, and SHIFT. See their description above...
The NVSS source catalog is searched within some search radius for
sources with flux density greater than specified, and small fields are
created around these sources. In order to do this, the position (RA,
DEC) of the pointing phase center is required. This is obtained from
the input UV data set. In the case of a single-source data set, it is
read from the header. In the case of a multi-source data set, the
source must be specified in the first element of the adverb SOURCES, and
the position is read from the SU extension. The selection of sources is
controlled by the adverbs BPARM(4), BPARM(5)< BPARM(6). See their
description above. The source catalog may be specified in INLIST or
you may use one of the AIPS-provided versions of the NVSS. The format
of the file is:
All lines beginning with a semi-colon are ignored. They are the
copyleft, a descriptive text in the AIPS files, and other comments.
Be careful about the epoch of the coordinates.
Remaining give the Right ascension in degrees, Declination in degrees,
Flux in mJy, and optionally a FWHM in arc seconds using format
F9.5,1X,F9.5,I7,F10.4. A sample is given below no width is shown
since none are used by SETFC.
0.08521 55.65239 1518
0.22108 40.90052 1301
0.84166 -17.45316 2415
1.23802 12.80524 1071
1.37727 69.39949 1105
1.55780 -6.39310 2051
1.59416 -0.07363 3898
2.12217 -5.97935 1323
358.54728 32.91998 1183
358.59049 45.88455 1873
358.78961 49.83570 2306
358.97312 15.69069 1104
359.25280 -34.75882 1286
359.32748 14.76875 1020
359.38022 -11.42748 1814
359.64781 44.07789 1940
PRIMARY BEAM PARAMETERS
SETFC corrects an image for the primary beam attenuation of
the antennas. The function used to model the primary beam for normal
VLA frequencies
F(x) = 1.0
+ parm(3) * 10E-3 * x
+ parm(4) * 10E-7 * x*x
+ parm(5) * 10E-10 * x*x*x
+ parm(6) * 10E-13 * x*x*x*x
+ parm(7) * 10E-16 * x*x*x*x*x
where x is proportional to the square of the distance from the
pointing position in units of [arcmin * freq (GHz)]**2, and F(x)
is the multiplicative factor to divide into the image intensity at the
distance parameter x. For other antennas, the user may read
in appropraite constants in PBPARM(3) through PBPARM(7). The
flag, PBPARM(2) must be set to a positive number to invoke this
option and PBPARM(3) must not be zero.
This correction scales with frequency and has a cutoff
beyond which the map values are set to an undefined pixel value GIVEN
in PBPARM(1). At the VLA frequencies the default cutoff is
1.485 GHz 29.8 arcmin
4.885 GHz 9.13 arcmin
15 GHz 2.95 arcmin
22.5 GHz 1.97 arcmin
and occurs at a primary beam sensitivity of 2.3 percent of the value at
the beam center. Corrections factors < 1 are forced to be 1.
The estimated error of the algorithm is about 0.02 in (1/F(x))
and thus leads to very large errors for x>1500, or at areas
outside of the primary response of 20 percent. The cutoff level
may be specified with DPARM(1).
Default values of PBPARM for the VLA are given by Perley's fits:
0.0738 GHz -0.897 2.71 -0.242
0.3275 -0.935 3.23 -0.378
1.465 -1.343 6.579 -1.186
4.885 -1.372 6.940 -1.309
8.435 -1.306 6.253 -1.100
14.965 -1.305 6.155 -1.030
22.485 -1.417 7.332 -1.352
43.315 -1.321 6.185 -0.983
For the ATCA, these are by default:
1.5 GHz -1.049 4.238 -0.8473 0.09073 -5.004E-3
2.35 -0.9942 3.932 -0.7772 0.08239 -4.429E-3
5.5 -1.075 4.651 -1.035 0.12274 -6.125E-3
8.6 -0.9778 3.875 -0.8068 0.09414 -5.841E-3
20.5 -0.9579 3.228 -0.3807 0.0 0.0
For the Karl G Jansky VLA ("EVLA"), the defaults are frequency
dependent. If the observing frequency is between two tabulated
frequencies, then the beam is computed for each of the tabulated
frequencies and then interpolated to the observing frequency. The
values used are far too numerous to give here, see EVLA Memo 195,
"Jansky Very Large Array Primary Beam Characteristics" by Rick Perley,
revision dated June 2016. Obtain it from
http://library.nrao.edu/evla.shtml
RICK PERLEY'S (OLD) REPORT
Polynomial Coefficients from LSq Fit to VLA Primary
Beam raster scans.
Functional form fitted:
1 + G1.X^2 + G2.X^4 + G3.X^6
where X = r.F,
and r = radius in arcminutes
F = frequency in GHz.
Fits were made to 3 percent cutoff in power for 24 antennas.
Poor fits, and discrepant fits were discarded, and the most
consistent subset of antennas had their fitted coefficients
averaged to produce the following 'best' coefficients.
Freq. G1 G2 G3
0.0738 -0.897E-3 2.71 E-7 -0.242E-10
0.3275 -0.935 3.23 -0.378
1.285 -1.329 6.445 -1.146 *
1.465 -1.343 6.579 -1.186
4.885 -1.372 6.940 -1.309
8.435 -1.306 6.253 -1.100
14.965 -1.305 6.155 -1.030
22.485 (old) -1.350 6.526 -1.090 *
22.485 (new) -1.417 7.332 -1.352
43.315 -1.321 6.185 -0.983
The estimated errors (from the scatter in the fitted
coefficients) are generally very small:
G1: .003 at all bands except Q (.014)
G2: .03 to .07 at all bands except Q (.15)
G3: .01 to .02 at all bands except Q (.04)
R. Perley 21/Nov/00
* The 1.285 and 22.485 old feed values are not used.