Single-binary star separation by ultraviolet color index diagrams

Abstract

Detection of a composite flux in photometry can serve as an indication of a photometrically unresolved binarity and can contribute to the parameterization of the components of binary systems. A main goal of the present study is to develop a method of automatic photometric detection of binaries, based on multi-color photometry, theoretical stellar spectral energy distributions and general understanding of binary evolution. In particular, we consider an ultraviolet photometry where, in combination with optical and infrared photometry, interstellar reddening can be easier distinguished from temperature reddening.

The following procedure is applied to achieve the declared goal. One can compose possible pairs of components, based on evolution concept. This can be done for various stages of binary evolution. Theoretical spectral energy distributions and response functions of ultraviolet photometric bands in appropriate sky surveys allow us to compute color-indices of such pairs, when they are unresolved, as well as of single stars. Usage of an interstellar extinction law gives us theoretical color-indices of reddened objects, both single stars and unresolved binaries. When plotted on a multidimensional color space, they allow us to indicate areas, where unresolved binaries can be easily separated from single stars, and identify binaries among objects, cross-matched in photometric surveys.