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| Joint Astronomy Centre |
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Reducing ACSIS data with CLASS
To run the GILDAS software
(class, greg, etc) first type (or enter this in your .login file):
The latest installed version (October 2009a) can be reached at all 64-bit
machines.
If you prefer to use CLASS and other Gildas software to reduce your spectra these
are the steps to take:
(at this moment one is working in Grenoble on methods to do the conversion in CLASS itself)
First make cubes of the ACSIS data with makecube or ORACDR.
Then extract subcubes of dimension 1,1,nspec from the cubes in NDF format and
convert these to FITS format.
Read the FITS files into CLASS. This can be done with the kappa command ndfcopy and the convert command ndf2fits. The following assumes that you are using the most recent (Lehuakona) release of the Starlink software (the exten parameter of ndfcopy is only available in Hilo). to FITSIf you have multisubsystem observations made with RxA3, where the first subband is in LSB (USB) and another is in USB (LSB), you have to change the sideband in the header of the USB (LSB) cube: kappa The simplest ways to convert .sdf files to FITS format is for: RxA3 and RxW (single spectra): convert ndf2fits file.sdf file.fits encoding="fits-class"RxA3, HARP, RxW (maps) - one single spectrum from position (1,1) in map: kappa ndfcopy in='file(1,1,)' out=file.sdf exten ./cubecopy file.sdf file_cc.sdfThe parameter exten in ndfcopy extracts header arrays correctly when copying the cubes. Cubecopy copies the cube, and updates the median values of the FITS header parameters MEDTSYS, EFF_EXP, and EFF_TIME. To convert maps one needs to do this for all positions in the map. This is an example of a csh script that does that for a 4x4 map: #!/bin/csh -f source /star/etc/login >& /dev/null source /star/etc/cshrc >& /dev/null kappa >& /dev/null convert >& /dev/null if (`alias kappa` == "") then echo "" echo "Fatal: Initialization error of kappa environment" echo "" exit endif @ i = 0 while ($i <= 3) @ j = 0 while ($j <= 3) ndfcopy in='file('${i}','${j}',)' out=file_${i}_${j}.sdf ./cubecopy file_${i}_${j}.sdf file_cc_${i}_${j}.sdf The size of a cube and pixel bounds can be found with the kappa command ndftrace, e.g. Dimension size(s): 45 x 45 x 2048 Pixel bounds : -23:21, -23:21, -1024:1023 to CLASS
These files can be converted into class format %class (note: if the scannumber is missing in the fits header one needs to give a number when writing to the output file, or it will be put to 1) If you have large maps it is useful to do the conversion to class format with a commandfile, e.g.%ls *.fits > files.classand then edit files.cfits with your favourite editor from file.fitsto fits read file.fitsthen %classto start class LAS90>@files.class ProblemsCurrently there are some problems with the FITS files converted in this way. Some header variables don't have the expected name in the FITS files. To correct this, enter in CLASS before reading the file:LAS90> sic\symbol OBSNUM NUMBER LAS90> sic\symbol MEDTSYS TSYS LAS90> sic\symbol EXP_TIME OBSTIME LAS90> sic\symbol LINE NOTAKEY LAS90> sic\symbol MOLECULE LINENote: The scan number is missing (and put to 1 by class) when the ACSIS spectrum is the sum of many spectra. There is a FITS keyword LINE, but it is empty. Other header parameters which are missing are: tau (not calculated for ACSIS data) weather parameters beameff forweffAll class spectra will have the observed position in the header (offsets are 0 0 for every position in a map). So in class one may want to modify the positions: In order to do that one has to modify the projection to 'none' (0). set var pos wr let proj 0 modi pos hh:mm:ss.ss dd:mm:ss However in the current class version (oct09a) there is a bug - the resulting RA offset is 24h too large. Because of limitations of the CLASS headers, observations made with very large radial velocities will have incorrect velocities and velocity resolutions in CLASS. It is recommended in such cases to observe with a calcalated sky frequency and velocity 0 km/s. For help within class, greg, etc type help, or look at the GILDAS homepage. In the newest version of Greg/Graphic the Explain command is not working. Here is a list of available tasks (run task). Jan Wouterloot |