Separating the spectra of binary stars

We present a practical method for the analysis of spectroscopic binaries, reconstructing the lines of the two components of the system. We show that the problem of the separation of binary spectra can be solved in an easy way, under most common conditions. One pair of observations may be sufficient, if taken at different orbital phases of the system, preferably at opposite quadratures. The separation procedure is discussed analytically, and a technique is described, which allows to restore the secondary lines in few steps. An algorithm is also provided, which derives the radial velocity of the secondary star, by directly analysing a difference line-profile obtained from the two input spectra. The efficiency of the method is tested, by reconstructing artificial line-profiles and simulated binary spectra as well. Then the procedure is applied to the eclipsing binary IZ Per, revealing for the first time its faint secondary spectrum.