Detection of planetary signals by reflected light of the host star using the autocorrelation of spectra
We consider an alternative to the cross-correlation function (CCF), that uses the autocor- relation function (ACF), to measure in spectra the reflected light of the stars by their planetary companion. The objective of this work is to assess and analyse the efficiency of the ACF in detecting planetary signals by a detection of reflected light. To do so, we first compare the ACF and the CCF using artificial spectra containing a planetary signal. We then use the ACF to analyse spectra of the 51 Peg + 51 Peg b system and compare our results with those obtained by Martins et al. (2015) who previously analysed the same system using the CCF. The functionalities of the ACF and the way it is implemented are similar to that of the CCF. One of the main advantages of the ACF is the fact that, unlike the CCF, no weighted binary mask is required. This makes the ACF easier to use. The results related to simulated spectra showed that the ACF allowed us to decrease the boundary condition threshold for the use of spectra compared to the CCF so that more data could be used to recover the planetary signal. For the 51 Peg b planet, we achieved a detection significance of 5.52 σnoise with the ACF compared to 3.70 σnoise with the CCF (Martins et al. 2015). We conclude that the ACF has the potential to become a prominent technique in detecting exoplanets considering its efficiency, ease of use and rapid execution time.