Fitting Formulae for the Effects of Binary Interactions on Lick Indices and Colours of Stellar Populations

More than about 50% stars of galaxies are in binaries, but most stellar population studies take single star-stellar population (ss-SSP) models, which do not take binary interactions into account. In fact, the integrated peculiarities of ss-SSPs are various from those of stellar populations with binary interactions (bs-SSPs). Therefore, it is necessary to investigate the effects of binary interactions on the Lick indices and colours of populations detailedly. We show some formulae for calculating the difference between the Lick indices and colours of bs-SSPs, and those of ss-SSPs. Twenty-five Lick indices and 12 colours are studied in the work. The results can be conveniently used for estimating the effects of binary interactions on stellar population studies and for adding the effects of binary interactions into existing ss-SSP models. The results and a few procedures can be obtained on request to the authors or via http://www.ynao.ac.cn/~bps/zhongmu/download.htm