A new algorithm for differential photometry: computing an optimum artificial comparison star

Our new algorithm for differential photometry solves the problem of identifying proper comparison stars without a prior detailed study of the field of view. The comparison stars' variability is determined in a self-consistent way, and their weighted average is used as a reference level. The maximum error in differential photometry using objects and reference stars of different spectral types is estimated. The results from these calculations show that the photometric band chosen greatly determines the level of accuracy achieved. Finally, an important application of high-precision differential photometry are planetary transits.