AIPS HELP file for MOMNT in 31DEC24
As of Fri Apr 26 17:06:12 2024
MOMNT: Task to calculate profile moments
INPUTS
INNAME Input name(name).
INCLASS Input name(class).
INSEQ 0.0 9999.0 Input name(seq. #). 0=>high
INDISK 0.0 4.0 Input disk drive #. 0=>any
OUTNAME Output name(name).
OUTCLASS Contains a string of numbers
(0-3) indicating which
moments are wanted.
blank => '012'
OUTSEQ -1.0 9999.0 Output name(seq. #).
0=>highest unique.
OUTDISK 0.0 4.0 Output image disk drive #
0=>highest with room.
BLC 0.0 2048.0 Bottom left corner of image
0=>entire image
TRC 0.0 2048.0 Top right corner of image
0=>entire image
FUNCTYPE Smoothing functions to be
used for blanking;
1st char refers to velocity
coord: B:box, H:Hanning;
2nd char refers to spatial
coords: B:box, G:Gaussian.
CELLSIZE 0.0 25.0 Width of smoothing functions:
1st element: velocity coord
2nd element: spatial coords
Allowed ranges:
Vel. B/H: odd integer 1-25
Spat. G: real 0.5-6.0.
B: odd integer 1-11
FLUX Use only data > FLUX
ICUT Use only data > in abs value
than ICUT (> 0). Use only
data < in abs value than
ICUT (< 0.).
PBPARM Beam parameters:
(1) Cutoff: 0 -> no PB corr
(2) > 0 -> Use (3)-(7)
(3)-(7) Beam shape
HELP SECTION
MOMNT
Type: Task
Use: MOMNT does profile analysis on spectral line data. It
calculates profile moments 0 to 3 from n-dimensional maps
(2TO BE 'VE', 'FR', or 'CH'; a subimage may be selected. The
decision on whether or not to include a particular point in the
moment calculation is made by comparing the smoothed/averaged
intensity at that point with FLUX and ICUT. The
smoothing/averaging is done in three dimensions, with a choice
of Boxcar or Hanning for the velocity coordinate, and Boxcar or
Gaussian for the spatial coordinates (specified by FUNCTYPE).
The size of the convolving kernel is given by CELLSIZE and has
to be an odd integer, except for the Gaussian where it specifies
the FWHM of the kernel; in this case the size of the kernel is
2*CELLSIZE(2)+1. The maximum kernel size for velocity is 25,
for the spatial coordinates 11. The kernel sizes are adjusted
to the nearest extremum if they are out of bounds. The subimage
size is adjusted for the spatial kernel size, if necessary. The
program makes an effort to minimize the I/O; if
(TRC(1)-BLC(1)+1+CELLSIZE(1)) * CELLSIZE(2) *
(TRC(2)-BLC(2)+1+CELLSIZE(2)) > 4000000
the execution time will about double because of a huge increase
in I/O (corners and kernel sizes adjusted, of course). For FLUX
try a value in the range
1.5 to 4 * RMS / SQRT (A * B)
where:
A = CELLSIZE(1) for velocity Boxcar
= (CELLSIZE(1)+1)/2 for velocity Hanning
B = CELLSIZE(2)**2/(B1*B2) for spatial Boxcar
= CELLSIZE(2)**2/(B1*B2) + 1 for spatial Gaussian
B1 = major axis FWHM of input map beam (in pixels)
B2 = minor axis FWHM of input map beam (in pixels)
RMS = r.m.s. noise in input map
The units of the first input axis must be m/s, Hz, or channel
number. XMOM is similar to MOMNT but does not do any smoothing
before the clipping.
*************************************************************
MOMNT now (2003-06-01) finally handles magic-value blanks.
Using REMAG to convert blanks to zero and then smoothing with
them is not correct and is no longer required.
*************************************************************
Users should be aware that the image of the first moment is in
single-precision floating point. If the first axis is frequency,
there may be not be enough accuracy to represent the variation in
frequency about some very high central frequency. The task will
subtract the central value from the image of the first moment
whenever the difference in the axis values from one end to the
other is < 10**-3 of the central value. NOTE: THIS PRODUCES AN
INCORRECT FIRST MOMENT SINCE AIPS HEADERS NO LONGER SUPPORT THE
CONCEPT OF A BIAS AND SCALE.
Adverbs:
INNAME.....Input name (name): Standard defaults.
INCLASS....Input name (class); Standard defaults.
INSEQ......Input name (sequence number); 0 => highest.
INDISK.....Input disk unit number; 0 => any.
OUTNAME....Output name (name): Standard defaults.
OUTCLASS...Contains a string of numbers (0-3) indicating which
moments are wanted (e.g., '0123' or '301');
N.B. blank => '012'. The actual OUTCLASSes of the
images will be 'MOM0','MOM1','MOM2',and 'MOM3'.
OUTSEQ.....Output name (sequence number); 0 => highest unique.
OUTDISK....Output disk unit number; 0 => highest w room.
BLC........Bottom left corner of subimage; 0: bottom left corner of
entire image
TRC........Top right corner of subimage; 0: top right corner of
entire image
FUNCTYPE...Smoothing functions to be used for blanking;
first character refers to velocity coordinate:
B:box, H:Hanning (default B);
second character refers to spatial coordinates:
B:box, G:Gaussian (default B).
CELLSIZE...Width of smoothing functions;
first element: velocity coordinate; allowed range:
B/H: odd integer 1 - 25 (<= 0 => 3);
second element: spatial coordinates; allowed ranges:
B: odd integer 1 - 11 (<= 0.0 => 5),
G: real 0.5 - 6.0 (<= 0.0 => 2.0).
FLUX.......A flux cutoff in the same units as the input image (i.e.
Jy/beam). Data values below FLUX in the smoothed image
are ignored in the moment computation. NOTE that 0.0 is
not a null value. Instead, it means ignore all negative
brightnesses.
ICUT.......A flux cutoff in the same units as the input image (i.e.
Jy/beam). When ICUT > 0.0, data values in the smoothed
image less in absolute value than ICUT are ignored. When
ICUT < 0.0, data values in the smoothed image greater in
absolute value than ICUT are ignored. NOTE that ICUT and
FLUX are both always used.
PBPARM.....Primary beam parameters: Adjust the cutoff levels to
account for the primary beam.
(1) Lowest beam value to believe: 0 -> do not do a
primary beam correction. The maximum correction is
a factor of 100.
(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
EXPLAIN SECTION
MOMNT has the option of scaling the cutoff values on a
pixel-by-pixel basis to "correct" for the primary beam. Thus, as the
beam value goes down the cutoff value goes up. This allows MOMNT to
be run on data cubes after the application of PBCOR. Since the
primary beam is a function of frequency, the spectral moments are
affected by the primary beam correction. Unfortunately this
correction also raises the noise, making the option to raise the
cutoff useful.
MOMNT 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
1.285 -1.329E-3 6.445E-7 -1.146E-10 *
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.