AIPS HELP file for SDVEL in 31DEC24
As of Fri Apr 19 16:27:40 2024
SDVEL: Task to shift spectral-line data to a given velocity
INPUTS
INNAME Input UV file name (name)
INCLASS Input UV file name (class)
INSEQ 0.0 9999.0 Input UV file name (seq. #)
INDISK 0.0 9.0 Input UV file disk unit #
OUTNAME Output UV file name (name)
OUTCLASS Output UV file name (class)
OUTSEQ 0.0 9999.0 Output UV file name (seq. #)
OUTDISK 0.0 9.0 Output UV file disk unit #
FLAGVER Flag table version
TIMERANG Time range to include
DPARM Compute and debug controls
(1) 0 -> velocity set at 1st
record of each scan
1 -> velocity set at last
record of each scan
2 -> velocity set at last
record of each scan
preceeding an OFF
3 -> velocity set at 1st
record of data set
(2) 0 -> use ref. coordinate
1 -> use coordinate of
record
2 -> use coordinate in
COORDINA
(3) Issue warning if shift >
DPARM(3) channels.
(4) Flag if shift > DPARM(4)
channels. 0 -> Nchan
COORDINA Velocity reference RA/dec
BADDISK 0.0 9999.0 Disks to avoid for scratch
HELP SECTION
SDVEL
Task: Shift a single-dish uv spectral-line data set in frequency space.
The purpose of the task is to shift all spectra to a given
velocity for the directions of observation. This task assumes
that the telescope has tracked - at some interval - the time
variation of frequency to maintain an approximately constant
velocity for the reference coordinate. It then shifts each
spectrum so that the reference velocity wrt the actual observed
coordinate is in the reference channel.
This is a subtle effect, previously ignored in spectral-line
imaging. However, for a coordinate 1.4 degrees from the
reference (e.g., a 2 degree square field with a center
reference), the error can be as large as 1.16 km/sec (LSR
velocities) or 0.79 km/sec (heliocentric) observed with NRAO's
12m telescope. Both vary with time, reference coordinate, and
telescope; the LSR velocity error changes significantly with time
of year. Narrow-band observations of wide fields, such as
observations of cold molecular regions, may be seriously affected
by this effect. Fortunately, so long as the spectra are fully
sampled in frequency, this effect can be fully corrected in
single-dish data. interferometer users are not so lucky.
Adverbs:
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 => highest.
INDISK.....Disk drive # of input UV file. 0 => any.
OUTNAME....Output UV file name (name). Standard defaults.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #). 0 => highest.
OUTDISK....Drive # of output UV file. 0 => highest with
space for the file.
FLAGVER....specifies the version of the flagging table to be applied.
0 => highest numbered table.
<0 => no flagging to be applied.
TIMERANG...Time range to include: start day, hour, minute, second, end
day, hour, minute, second. end = 0 -> infinity.
DPARM......Controls:
(1) Tells the task when to compute the reference doppler
shift as
0 -> at the starting record of EACH scan
1 -> after each scan using the last time of the scan but
applying it to the next scan
2 -> on each "off" scan (detected by a missing scan number)
using the last coordinate before the off.
3 -> at the first record of the data set.
The 12m probably now uses mode 0, it used to use mode 2.
(2) Tells the task what coordinate to use in the Doppler
computation as
0 -> data set reference coordinate
1 -> coordinate of the particular record
2 -> user specified coordinate in COORDINA
The 12m used to use mode 1, now uses mode 0, but can use
mode 2.
(3) A warning is issued if the shift exceeds DPARM(3)
channels. 0 -> NCHAN/20. The task limits the number of
consecutive samples warned to 10 but if there are then good
samples, it will resume warnings on the next "bad".
(4) A sample is deleted if the shift exceeds DPARM(4)
channels. 0 -> NCHAN. This may be used to detect and flag
periods in which the antenna is blown way off course
.
COORDINA...The RA and declination coordinates are found as:
RA = abs(CO(1)) + abs(CO(2))/60 + abs(CO(3))/3600
if any of CO(1), CO(2), CO(3) < 0: Xpos = -Xpos
Dec = abs(CO(4)) + abs(CO(5))/60 + abs(CO(6))/3600
if any of CO(4), CO(5), CO(6) < 0: Ypos = -Ypos
The units are standard FITS units (e.g degrees) except
that right ascensions are in hours of time.
BADDISK....A list of disks on which scratch files are not to be
placed. This will not affect the output file.
EXPLAIN SECTION