THE POTENTIAL IMPORTANCE OF BINARY EVOLUTION IN ULTRAVIOLET-OPTICAL SPECTRAL FITTING OF EARLY-TYPE GALAXIES

Abstract

Binaries are very common in galaxies, and more than half of Galactic hot\nsubdwarf stars, which are thought as a possible origin of UV-upturn of old\nstellar populations, are found in binaries. Previous works showed that binary\nevolution can make the spectra of binary star populations significantly\ndifferent from those of single star populations. However, the effect of binary\nevolution has not been taken into account in most works of spectral fitting of\ngalaxies. This paper studies the role of binary evolution in spectral fitting\nof early-type galaxies, via a stellar population synthesis model including both\nsingle and binary star populations. Spectra from ultraviolet to optical band\nare fitted to determine a few parameters of galaxies. The results show that the\ninclusion of binaries in stellar population models may lead to obvious change\nin the determination of some galaxy parameters and therefore it is potentially\nimportant for spectral studies. In particular, the ages of young components of\ncomposite stellar populations become much older when using binary star\npopulation models instead of single star population models. This implies that\nbinary star population models will measure significantly different star\nformation histories (SFHs) for galaxies compared to single star population\nmodels. In addition, stellar population models with binary interactions measure\nlarger dust extinctions than single star population models on average. It\nsuggests that when using binary star population models instead of single star\npopulation models, negative extinctions are possibly unnecessary in spectral\nfitting of early-type galaxies.\n