Type Ia Supernovae as Standard Candles Annu. All rights reserved 2. It should be pointed out that the photometry of supernovae is particularly difficult. Photographic photometry requires the setup of an auxiliary local standard sequence. Any zero-point and scale errors in this sequence translate into a magnitude shift and a distortion of the light curve.
Photoelectric photometry is sensitive to the background light of the parent galaxy.
Even CCD photometry is not above suspicion. The transient phenomenon of a supernova frequently requires the use of nonphotometric nights which do not allow the proper determination of the night's photometric coefficients. Bewildering differences between the photometry of the same supernova by different authors give a vivid illustration of these problems. Deviations from the template in one pass band, for a supernova that appears standard in the other pass bands, are likely to be the result of photometric errors. In general the true deviations from the templates must be smaller than observed.