code: def compute_photometry(catalog, photmode):
      
      # Determine VEGAMAG zero-point using pysynphot for this photmode
      photmode = photmode.replace(' ', ', ')
      vega = S.FileSpectrum(VEGASPEC)
      bp = S.ObsBandpass(photmode)
      vegauvis = S.Observation(vega, bp)
      vegazpt = 2.5 * np.log10(vegauvis.countrate())
  
      # Use zero-point to convert flux values from catalog into magnitudes
      # source_phot = vegazpt - 2.5*np.log10(catalog['source_sum'])
      source_phot = vegazpt - 2.5 * np.log10(catalog['flux'])
      source_phot.name = 'vegamag'
      # Now add this new column to the catalog table
      catalog.add_column(source_phot)
  
      return catalog
docs: Compute magnitudes for sources from catalog based on observations photmode.
  
      Parameters
      ----------
      catalog : `~astropy.table.Table`
          Astropy Table with 'source_sum' column for the measured flux for each source.
  
      photmode : str
          Specification of the observation filter configuration used for the exposure
          as reported by the 'PHOTMODE' keyword from the PRIMARY header.
  
      Returns
      -------
      phot_cat : `~astropy.table.Table`
          Astropy Table object of input source catalog with added column for
          VEGAMAG photometry (in magnitudes).