TIRAVEL - Template-independent RAdial VELocity measurement

We propose a new approach to measure differential radial velocities, mainly for single-lined spectroscopic binaries. The proposed procedure - TIRAVEL (Template-Independent RAdial VELocities) - does not rely on a prior theoretical or observed template, but instead looks for a set of relative Doppler shifts that simultaneously optimizes the alignment of all the observed spectra. We suggest a simple measure to quantify this overall alignment and use its maximum to measure the relative radial velocities. As a demonstration, we apply TIRAVEL to the observed spectra of three known spectroscopic binaries, and show that in two cases TIRAVEL performs as good as the commonly used approach, while in one case TIRAVEL yielded a better orbital solution.