AliasFinder: A Python script to search for the true planetary frequency within radial velocity data

Planets around other stars, so called exoplanets, can be detected with the radial velocity (RV) method which uses high-resolution spectroscopy on the host star. The method transforms the measured Doppler-shift in a stellar spectrum to a radial velocity. This Doppler-shift is caused by the stellar reflex motion (wobbling), in particular the line of sight movement of the star, due to its gravitational interaction with the orbiting planet. By now the RV method is the second most successful method and the first one to find exoplanets. The detection of exoplanets by this method relies on finding periodic signals in noisy time-series data (RVs over time) using a periodogram analysis. However, gaps in the observations (e.g., stars can only be observed during night from the ground) can result in strong aliases, an effect where two signals are almost indistinguishable when sampled. Aliases normally occur at fAlias = fTrue ±m · fSampling where fTrue is the true signal, fSampling the sampling frequency and m an integer value. This makes it difficult to assess the true period of the planet and has already led to incorrectly published orbital periods (see Dawson and Fabrcky 2010; Stock et al. in prep).