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Integrated spectral energy distributions of binary star composite stellar populations

This paper presents theoretical integrated spectral energy distributions (SEDs) of binary star composite stellar populations (bsCSPs) in early-type galaxies, and how the bsCSP model can be used for spectral studies of galaxies. All bsCSPs are built basing on three adjustable inputs (metallicity, ages of old and young components). The effects of binary interactions and stellar population mixture are taken into account. The results show some UV-upturn SEDs naturally for bsCSPs. The SEDs of bsCSPs are affected obviously by all of three stellar population parameters, and the effects of three parameters are degenerate. This suggests that the effects of metallicity, and the ages of the old (major in stellar mass) and young (minor) components of stellar populations should be taken into account in SED studies of early-type galaxies. The sensitivities of SEDs at different wavelengths to the inputs of a stellar population model are also investigated. It is shown that UV SEDs are sensitive to all of three stellar population parameters, rather than to only stellar age. Special wavelength ranges according to some SED features that are relatively sensitive to stellar metallicity, young-component age, and old-component age of bsCSPs are found by this work. For example, the shapes of SEDs with wavelength ranges of 5110-5250AA, 5250--5310AA, 5310--5350AA, 5830--5970AA, 20950--23550AA are relatively sensitive to the stellar metallicity of bsCSPs. The shapes of SEDs within 965-985AA, 1005--1055AA, 1205--1245AA are sensitive to old-component age, while SED features within the wavelength ranges of 2185--2245AA, 2455--2505AA, 2505--2555AA, 2775--2825AA, 2825--2875AA to young-component age.