A Search for Optical Laser Emission Using Keck HIRES

We present a search for laser emissions coming from point sources in the vicinity of 2796 stars, including 1368 Kepler objects-of-interest (KOIs) that host one or more exoplanets. We search for extremely narrow emission lines in the wavelength region between 3640 and 7890 A using the Keck 10 m telescope and spectroscopy with high-resolution (λ/Δλ = 60,000). Laser-emission lines coming from nonnatural sources are distinguished from natural astrophysical sources by being monochromatic and coming from an unresolved point in space. We search for laser emissions located 2-7'' from the 2796 target stars. The detectability of laser emissions is limited by Poisson statistics of the photons and scattered light, yielding a detection threshold flux of ~1 photons m-2 min-1 for typical Kepler stars and ~1 00 photons m-2 min-1 for solar-type stars within 100 lt-yr. Diffraction-limited lasers having a 10 m aperture can be detected from 100 lt-yr away if their power exceeds 90 W, and from 1000 lt-yr away (Kepler planets), if their power exceeds 1 kW (from lasers located 60-200 AU, and 2000-7000 AU from the nearby and Kepler stars, respectively). We did not find any such laser emission coming from any of the 2796 target stars. We discuss the implications for the search for extraterrestrial intelligence (SETI).