Study of spectroscopic binaries with TODCOR. III. Application to triple-lined systems

In a previous paper we introduced TODCOR, a new two-dimensional correlation technique, to analyze spectra of binary stars and derive the Doppler shifts of the two components. We propose here a generalization of TODCOR to analyze spectra of triple-lined stellar systems and derive the Doppler shifts of the three components. The algorithm computes the correlation of the observed spectrum against combinations of three template spectra, with all possible shifts. Thus, the correlation is a three-dimensional function in velocity space. The location of the maximum of this function corresponds to the actual shifts of the three components. We demonstrate the difficulties of the one-dimensional cross-correlation and the advantages of the new algorithm with a simulated example. We also analyze with the algorithm a real test case, HD 100018, and we show that the velocities derived with the new extension of TODCOR solve a long-standing discrepancy between the old orbital elements and the mass estimate for the system.