The 2821 Star Southern Hemisphere HARPS Optical SETI Survey

We conducted a single observation survey of archival reduced spectra from 2821 stellar targets taken by ESO’s HARPS spectroscope for potential signatures of lasers from extraterrestrial civilizations. We established a classification system to identify false positives, including cosmic rays, bleed through from the Th-Ar calibration lamp, night sky airglow lines, and large clusters of emission lines which may be the product of natural stellar activity. Of the 2821 stellar spectra we analyzed, we identified 294 candidates with at least one narrow spectral emission feature–41 of which did not fit any of the above false positive categories. After filtering this dataset on the basis of linewidth, we were left with 9 compelling candidates–one of which closely matched a laser’s predicted spectral profile. This spurred a comprehensive investigation. We found 6 other occurrences of the same emission line in observations of unrelated stars separated in the sky by several hours of right ascension within a two hour window on the same night, which does not appear to be in the same reference frame as any of these stars. Although this latest result argues against an interstellar origin, the deductive detective work itself yielded methodologies that are broadly applicable to future candidates of this type. It also spurred some novel theoretical hypotheses/predictions about what a laser technosignature might look like which can motivate future search strategies. Additionally, the continued lack of an alternative prosaic explanation still singles it out as an anomaly which could point to a novel natural atmospheric phenomenon.