code: def get_aux_files(basename):
      
      base = os.path.splitext(basename)[0]
      files = {"bkg": base + "_bkg.fits",
               "rms": base + "_rms.fits",
               "mask": base + ".mim",
               "cat": base + "_comp.fits",
               "psf": base + "_psf.fits"}
  
      for k in files.keys():
          if not os.path.exists(files[k]):
              files[k] = None
      return files
docs: Look for and return all the aux files that are associated witht this filename.
      Will look for:
      background (_bkg.fits)
      rms        (_rms.fits)
      mask       (.mim)
      catalogue  (_comp.fits)
      psf map    (_psf.fits)
  
      will return filenames if they exist, or None where they do not.
  
      Parameters
      ----------
      basename : str
          The name/path of the input image.
  
      Returns
      -------
      aux : dict
          Dict of filenames or None with keys (bkg, rms, mask, cat, psf)