AIPS HELP file for CVEL in 31DEC22
As of Tue Dec 5 1:42:09 2023
CVEL: Task to shift spectral line data to a given velocity
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 #
SOURCES Source list to shift, other
sources will be passed
unshifted. Ignored for
single source files.
'*' or ' ' => all;
QUAL -10.0 Source qualifier to shift,
Sources with other quals
will be passed unshifted.
-1 => no selection by qual
TIMERANG Time range to shift
SELBAND Bandwidth to select (kHz)
SELFREQ Frequency to select (MHz)
FREQID 0.0 Freq. ID to select (1 only)
SUBARRAY 0.0 1000.0 Subarray, 0=>1
FLAGVER Flag table version
DOBAND -1.0 10.0 If >0 apply bandpass cal.
Method used depends on value
of DOBAND (see HELP file).
BPVER Bandpass table version
GAINUSE CL table version which
contains the time/antenna
dependent frequency offsets.
0 => 1.
APARMS(1:6) will define the
velocity parameters needed
for single source files. The
parameters you define here
will override any of those
set with ALTDEF. If any of
APARM(1)-(6) are set CVEL
will assume all are set.
These are ignored in the case
of multi-source files, you
should use SETJY for them.
APARM (1) => for single source file
the velocity of a given
(2) => the pixel to which
(3) defines the velocity type
0 => LSR, 1 => HELIO
(4) the velocity definition:
0 => optical, 1 => radio
(5) aparms 5 & 6 define the
rest frequency of the
line in Hz; the value
used is the sum of
APARM(5) + APARM(6).
(7) not used now
(8) if > 0 then do not print
messages about large
channel shifts, used if
deliberately want a large
(9) 0 => not smooth spectra
>0 => smooth AC spectra
>1 => smooth XC spectra
by Hanning also
(10) 0 = trust CVEL
1 = Earth center
2 = Low antenna
3 = High antenna
BADDISK 0.0 9999.0 Disks to avoid for scratch
Task: Shift a uv spectral line data set in frequency space. The
purpose of the task is to shift all spectra to a given
velocity; this will correct data observed with a fixed
frequency for the effects of the Earth's rotation and its
motion within the Solar System and towards the Local Standard
CVEL will work on both single and multi-source files. For
multi-source files the velocity to which the spectra are to be
shifted should be entered into the source (SU) table using the
task SETJY, this should be done for each source you wish to
shift. You then specify those sources with the SOURCE command
in CVEL, all other sources will be written to the output uv
file with their spectra unshifted. For single source files the
necessary velocity data are passed to the task using APARM(1) -
The shift that is reported is a shift of the profile with
respect to the channels, i.e. a shift of -0.4 will shift the
profile to the left.
The task will attempt to determine if it is processing data
from the VLBA correlator by examining the ANAME keyword in the
AN(tenna) table. If it is 'VLBA' then CVEL assumes that all
data have been fringe-rotated to the same reference point (the
centre of the Earth) and will determine the velocity correction
NOTE: this task optionally applies bandpass and flag tables to
the data but does not apply SN/CL calibration tables,
polarization, baseline-cals, etc. Run SPLIT first if these
operations are desired.
This task supports moving sources if there is a PO table.
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.
SOURCES....Source list to shift. All sources named will be
shifted to the velocity found in the SU table.
All other sources will be passed to the output
file unshifted. Ignored for single source files.
Some rules apply: '*' or ' ' = all;
a "-" before a source
name means shift all except ANY source named.
QUAL.......Only sources with a source qualifier number in the
SU table matching QUAL will be used.
If QUAL is -1, then selection by a qualifier
is ignored. Selection by a qualifier is ignored
for single source file also.
TIMERANG...Time range of the data to be shifted. In order:
Start day, hour, min. sec,
end day, hour, min. sec. Days relative to ref.
SELBAND....Bandwidth of data to be selected. If more than
one IF is present SELBAND is the width of the
first IF required. Units = kHz. For data which
contain multiple bandwidths/frequencies the task
will insist that some form of selection be made
by frequency or bandwidth.
SELFREQ....Frequency of data to be selected. If more than
one IF is present SELFREQ is the frequency of the
first IF required. Units = MHz.
FREQID.....Frequency identifier to select. CVEL will process only
one frequency identifier, ignoring any others. You may
determine which is applicable from the OPTYPE='SCAN'
listing produced by LISTR. If either SELBAND or SELFREQ
are set, their values overide that of FREQID.
However, setting SELBAND and SELFREQ may result in
an ambiguity. In that case, the task will request
that you use FREQID.
SUBARRAY...Subarray number to use. 0=>1
FLAGVER....specifies the version of the flagging table to be
applied. 0 => highest numbered table.
<0 => no flagging to be applied.
DOBAND.....If true (>0) then correct the data for the shape of the
antenna bandpasses using the BP table specified by BPVER.
The correction has five modes:
(a) if DOBAND=1 all entries for an antenna in the table
are averaged together before correcting the data.
(b) if DOBAND=2 the entry nearest in time (including
solution weights) is used to correct the data.
(c) if DOBAND=3 the table entries are interpolated in
time (using solution weights) and the data are then
(d) if DOBAND=4 the entry nearest in time (ignoring
solution weights) is used to correct the data.
(e) if DOBAND=5 the table entries are interpolated in
time (ignoring solution weights) and the data are then
BPVER......Specifies the version of the BP table to apply.
GAINUSE....version number of the CL table from which CVEL will
extract the tima and antenna dependent frequency
offsets. For instance, if some attempt was made to
occasionally correct for the doppler offsets these
offsets would be recorded in the CL table. For CVEL
to determine the true observing frequency at any
given time it must add up the reference freq. in
the catalogue header, the IF offset freq for IF >
1, the peculiar source freq. offset and the time
and antenna dependent freq. stored in the CL table.
If the data have been SPLIT, or CLCAL has generated
a new CL table there is no guarantee that the time
dependent offsets will be taken into account.
0 => 1
The control information is used to specify the
necessary velocity parameters for single source
files. The parameters you define here will
override any of those you set with ALTDEF. If any
of APARM(1) to (6) are set then the task assumes
that all are set.
APARM(1): the velocity of a given pixel (channel)
in the spectrum (m/s).
APARM(2): the pixel (channel) to which APARM(1)
APARM(3): the velocity type, 0 => LSR,
1 => heliocentric
APARM(4): the velocity definition, 0 > optical,
1 => radio
APARM(5) & APARM(6): define the restfrequency of
the molecular transition in Hz; the value used
is the sum of APARM(5) and APARM(6) (need the
APARM(7): not used now
APARM(8): if > 0 then do not print messages about
large channel shifts, used if deliberately
want a large shift.
APARM(9): 0 => not smooth spectra while shifting
>0 => smooth autocorrelation spectra by Hanning
>1 => smooth cross-correlation spectra by Hanning
It is strongly recomended to smooth spectra in the case
of strong narrow features. Otherwise various ringing
effects including 180 degree phase jumps between
adjacent channels can occur.
APARM(10): The correlator must shift the frequency of one
or both antennas in a baseline to the same in order to
correlate. The VLBA coorelators among others shifts both
to the Earth's center. The JIVE EVN shifts the low
numbered one to the high numbered one. Others the
opposite. If you know what this about and know what your
correlator did then set this parameter:
1 => Earth center
2 => low numbered
3 => high numbered
The default sets 1 for VLBA, 3 for EVN, rest 2 based on
the array name in the antenna file. NOTE WELL - THIS
BUSINESS MEANS THAT IT IS VERY BAD TO RENUMBER ANTENNAS
IF THAT RENUMBERING CHANGES THEIR ORDER UNLESS THE EARTH
CENTER IS THE CORRECT CHOICE FOR THIS ARRAY.
BADDISK....A list of disks on which scratch files are not to
be placed. This will not affect the output file.