PMAP
Spectral line On-The-Fly (OTF) On-Off mapping mode. OTF is much more efficient for mapping than the point-by-point modes since it avoids much of the overhead involved in the latter methods. It should always be used for mapping extended sources since the efficiency rises with larger map sizes.
The PMAP command was designed to be very similar to the PRASTER mode. There are, however, a few very important differences about integration times and step sizes. For more information, please read the help on PMAP /TIME_PMA and PMAP /MAPSIZE_PMA carefully !
Syntax:
PMAP <reflong> <reflat> <refsystem>
/MAPSIZE_PMA <lon> <reslon> <lat> <reslat> <scan direction>
/TIME_PMA <Ton> <Toff>
/ON_OFFS <n on's per off> <f: on first>
/NOOFFSET
<reflong>:
Position offset in true angles in longitude for the reference position. Unit is arcseconds.
<reflat>:
Position offset in true angles in latitude for the reference position. Unit is arcseconds.
<refsystem>:
The reference system is specified either in the source coordinate system of the catalogue epoch (possibly rotated if a descriptive system is used):
SOURCE, BASIS, LAMDA, BETA are all equivalent inputs
or in the current horizontal system:
HORIZONTAL, AZIMUTH, ELEVATION are equivalent inputs.
/MAPSIZE_PMA <lon><reslon><lat><reslat><obs_system>:
Example: /MAPSIZE_PMA 100 5 80 10 LAM
The map is dimensioned 100x80 seconds of arc with a step size of 5 seconds of arc along the scanning axis (LAM) and 10 seconds of arc in the beta direction.
Be careful to choose the step along the scanning axis small enough so that no considerable beam smearing occurs. This step size should be a small fraction of the beam size.
The step size perpendicular to the scanning axis can be chosen freely. For best results it should be smaller than half the beam size. You can, however, later combine several coarsely spaced maps to get a fully sampled final map.
<lon><reslon>:
<lon> defines the length of a line in the lam-direction and <reslon> the distance between two lines or between rasterpoints.
<lat><reslat>:
This has the same meaning like <long><reslon>, but for the beta direction.
<obs_system>:
Chooses the scanning coordinate of the map. Possible values are:
LAM: scans in longitude, latitude is orthogonal axis BET: scans in latitude, longitude is orthogonal axis AZM: the same for azimuth and elevation ELV: the same for elevation and azimuth
/TIME_PMA <Ton><Toff>:
"Ton" specifies the time per OTF raster point. This is NOT the time per subscan ! A subscan consists of a series of OTF raster points and represents a full row or column of the map.
The total time for one OTF row / column (i.e. one "On" subscan) is Ton*lon/reslon (or Ton*lat/reslat for the other direction).
"Ton" translates into backend dump times. Currently, the minimum value for "Ton" is 2 seconds because of data rate limitations with the Vax / Camac system. Ideally, "Ton" should be between 2 and 6 seconds to get reasonable scanning velocities.
You will get more integration time per beam along the scanning axis because OTF maps are heavily oversampled. To get even more integration time you should repeat the full map several times. It is better to observe several short maps with intermediate calibrations than one long map because changes in the system and the atmosphere will be smaller.
"Toff" specfies the time to be spent on the reference position. If omitted, the reference time is calculated automatically and set to the optimum value of Ton*sqrt(Num of On's per Off).
/ON_OFFS <n on's per off><f: on first>:
Number of On's per Off. Currently, the map should start with an Off since the reduction software cannot yet handle other setups.
/NOOFFSET:
The ON observation is made at the position of the object specified by SOURCE without any offsets specified by the SET OFFSET command.