A Search for Laser Signals in Optical Stellar Spectra

Lasers provide a potentially energy efficient, powerful, and technologically simple form of transmitting and receiving information over interstellar distances, and thus are of special interest in the search for extraterrestrial intelligence. Past works have directly searched through the spectra of target stars for features that match the expected characteristics of laser signals: high intensity in a narrow wavelength band, gaussian shape due to travel through the telescope optics, and no clear natural explanation. Most have used observations from the Keck telescope. This project introduces a new method: by first matching the target spectrum to a library of spectra corresponding to stars with known properties, then subtracting a linear combination of the closest matching spectra from the target spectrum, we produce a residual which contains only features unique to the target spectrum. Examining the residual for laser signals will provide a more sensitive laser search than previously conducted. We also present a calibration of the laser search algorithm to demonstrate its wider applicability for analyzing Automated Planet Finder, rather than only Keck, observations.