Photometric biases due to stellar blending: implications for measuring distances, constraining binarity and detecting exoplanetary transits

摘要

We investigate blending, binarity and photometric biases in crowded-field CCDimaging. For this, we consider random blend losses, which correspond to thetotal number of stars left undetected in unresolved blends. We present a simpleformula to estimate blend losses, which can be converted to apparent magnitudebiases using the luminosity function of the analyzed sample. Because of theused assumptions, our results give lower limits of the total bias and we showthat in some cases even these limits point toward significant limitations inmeasuring apparent brightnesses of ``standard candle'' stars, thus distances tonearby galaxies. A special application is presented for the OGLE-II BVI maps ofthe Large Magellanic Cloud. We find a previously neglected systematic bias upto 0.2-0.3 mag for faint stars (V~18.0-19.0) in the OGLE-II sample, whichaffects LMC distance measurements using RR Lyrae and red clump stars. We alsoconsider the effects of intrinsic stellar correlations, i.e. binarity, viacalculating two-point correlation functions for stellar fields around sevenrecently exploded classical novae. In two cases, for V1494 Aql and V705 Cas,the reported close optical companions seem to be physically correlated with thecataclysmic systems. Finally, we find significant blend frequencies up to50-60% in the samples of wide-field exoplanetary surveys, which suggests thatblending calculations are highly advisable to be included into the regularreduction procedure.