code: def thermal_source(self):
          
          sp = (SourceSpectrum(BlackBody1D, temperature=self.temperature) *
                units.SR_PER_ARCSEC2 * self.beam_fill_factor * self)
          sp.meta['temperature'] = self.temperature
          sp.meta['beam_fill_factor'] = self.beam_fill_factor
          return sp
docs: Apply emissivity to an existing beam to produce a thermal
          source spectrum (without optical counterpart).
  
          Thermal source spectrum is calculated as follow:
  
              #. Create a blackbody spectrum in PHOTLAM per square arcsec
                 with `temperature`.
              #. Multiply the blackbody with `beam_fill_factor` and ``self``.
  
          Returns
          -------
          sp : `~synphot.spectrum.SourceSpectrum`
              Thermal source spectrum.