Conversion of map cubes to FITS

 SPECX has the capability to convert data cubes into FITS, either as velocity slices or complete cubes via the write-fits-map (w-f-m) and write-fits-cube (w-f-c) commands. The latter is a relatively recent addition and seems to work well generally.

w-f-m creates velocity slices i.e. maps of intensity versus position over a specified velocity range, say. Having decided on the velocity increment to use, and whether to use integrated or peak line strengths, one first opens a FITS file with the command open-fits. The name given the FITS file is quite literal; if you want the filetype to be .fits you have to specify it as shown in the examples below. Remember to close the FITS file with close-fits.

The following sequence is a typical example of how this would work:

 >> w-f-m
 Velo range? (km/s  ) [ -10.0000,   0.0000] -6 -4
 Integrated intensity? (rather than average) (Y/N) [Y] 
 R.A. offset scaled from   56.000 to  -56.000
 Dec. offset scaled from   56.000 to  -56.000
 Map centre as specified when map opened
 Centre channel VLSR (Rad def'n) -4.06757    
 Sector  1 : New I.F. = -1.500078 GHz
  -- specx_wrfitsmap --
     VFRAME  = LSR 
     VDEF    = RAD
     VELCODE = VLSR    
     VELREF  =   257
     Image frequency =     342796160906.77
     Deltav          =    -135.45202891868
 >> cl-fits
 >> $ls -l *.fits
-rw-r--r--   1 hem      astro      17280 Oct 13 23:19 src34.fits
 >>

w-f-c is also really very painless, and quite similar in mechanism to w-f-m:

 >> open-fits
 Filename for FITS output file? [src34.fits] src34_cube.fits
 Should disk file be byte-reversed? (Y/N) [Y] 
 >> w-f-c
 Flagged   50400 undefined pixels
 Map centre as specified when map opened
 Centre channel VLSR (Rad def'n) -26.3031    
 Sector  1 : New I.F. = -1.500000 GHz
  -- specx_wrfitscube --
     VFRAME  = LSR 
     VDEF    = RAD
     VELCODE = VLSR    
     VELREF  =   257
     Image frequency =     227537914962.07
     Deltav          =    -406.38704960595
 >> cl-fits
 >> $ls -l *.fits
-rw-r--r--   1 hem      astro      17280 Oct 13 23:19 src34.fits
-rw-r--r--   1 hem      astro    1016640 Oct 13 23:25 src34_cube.fits
 >>

Note the difference in size (given in bytes above) between map slices and cubes. The latter should be created carefully if you think diskspace is a problem. The above is a small (17 by 17 points, 700 channels) map, for reference.