Computing comet tail profiles

To derive tail profiles – e.g. to study asteroids or comets – I’ve developed a tail_profile.py code. It’s not in any of my usual SVN repos, so email me for a copy.

It’s run as follows:

/some/dir/tail_profile.py xxx.WEIGHTED.fits 200.6523 -15.765142 -save=test.dat -width=-3,3 -length=-200,1100 -fromregion=ds9.reg -sky=-40,-6/6,40

And this is what the parameters mean:

• xxx.WEIGHTED.fits
  Input file name. Has to be a single-extension FITS (i.e. run ODI frames through swarpstack first)
• 200.6253
  This is the RA position, in degrees, of the tail origin, i.e. the position of the nucleus
• -15.765
  Declination of Nucleus, in degrees
• -save=some.file
  File to write the profile data into. Output is written both as ASCII and FITS.
• -width=-3,3
  How wide the tail is. In this example, the tail spans from -3 to +3 arcseconds either side of the nucleus position
• -length=-200,1100
  Position along the tail to extract. In this case, from 200” ahead of the nucleus to 1100 arcsec behind the nucleus.
• -fromregion=ds9.reg
  Region file defining the angle of the tail. See below for details.
• -sky=-40,-6/6,40
  List of sky apertures extracted parallel to the tail, averaged, and subtracted from the tail profile. In this case, we use two apertures, extending from -40” to -6” from the tail and again from +6” to +40” (i.e. on the other side of the tail.

Note that only the input filename, Ra and Dec need to be given, and in that order. All other parameters are optional, and can be given in any order.

This is what the ds9 region file looks like overplotted (but slightly offset to show the tail) over some example image. Note that the region shape MUST be “line” (not vector or anything else).