A 2821 Star Optical SETI Survey using ESO HARPS archival data

Abstract

We examined archived observations of 2,821 stars taken by the high-resolution ESO HARPS spectrograph to search for potential narrow-band laser emissions from extraterrestrial sources. From one observation of each star, our search algorithm identified a total of 285 spectral peaks with line widths slightly larger than the instrument's point-spread function. After eliminating false positives (including cosmic rays, instrumental artifacts, and terrestrial airglow lines, we identified 8 sources worthy of follow-up observations. We then analyzed all 1,835 additional observations of these follow-up targets, looking for recurring signals. We found 1 additional unexplained candidate in this followup search, but no candidate spikes which repeated at the same wavelength as one of the initial candidates at a later time. Further analysis identified one candidate as a likely faint airglow line. The remaining seven candidates continued to defy all false positive categories, including interference by LiDAR satellites and adaptive optics lasers from neighboring observatories. However, observations of other stars on the same night showed identical spectral spikes (in the telescope's reference frame) for four of these seven candidates -- indicating an as-yet unknown terrestrial source. This leaves 3 final candidates which currently defy the prosaic explanations examined thus far, show no indication of a terrestrial origin and therefore warrant further investigation. Two of these three candidates originate from M-Type stars and one of them originates from an oscillating red giant, so follow-up work will need to disentangle natural astrophysical stellar processes from potential SETI sources.