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Search for Nanosecond Optical Pulses from Nearby Solar-Type Stars
With ``Earth 2000'' technology we could generate a directed laser pulsethat outshines the broadband visible light of the Sun by 4 orders ofmagnitude. This is a conservative lower bound for the technicalcapability of a communicating civilization; optical interstellarcommunication is thus technically plausible. We have built a pair ofsystems to detect nanosecond pulsed optical signals from a target listthat includes some 13,000 Sun-like stars, and we have made some 16,000observations totaling nearly 2400 hr during five years of operation. Abeam splitter-fed pair of hybrid avalanche photodetectors at the 1.5 mWyeth Telescope at the Harvard/Smithsonian Oak Ridge Observatory(Agassiz Station) triggers on a coincident pulse pair, initiatingmeasurement of pulse width and intensity at subnanosecond resolution. Anidentical system at the 0.9 m Cassegrain at Princeton's Fitz-RandolphObservatory performs synchronized observations with 0.1 μs eventtiming, permitting unambiguous identification of even a solitary pulse.Among the 11,600 artifact-free observations at Harvard, the distributionof 274 observed events shows no pattern of repetition, and is consistentwith a model with uniform event rate, independent of target. With onepossible exception (HIP 107395), no valid event has been seensimultaneously at the two observatories. We describe the search andcandidate events and set limits on the prevalence of civilizationstransmitting intense optical pulses.
| Interstellar Extinction Along the Camelopardalis and Perseus Border
Interstellar extinction in a ~ 100 sq. degree area at theCamelopardalis and Perseus border is investigated. The study is basedon the results of photoelectric photometry of 455 stars in theseven-color Vilnius photometric system published earlier. The nearest100 stars with Hipparcos parallaxes show that the extinction starts togrow at a distance of 110--150 pc. At a distance of 1 kpc theextinction A_V is within 1.2 and 2.4 mag. At larger distances theextinction determination is affected by the limiting magnitude effect.At distances >1.5 kpc a number of O--B stars with the extinctionsbetween 2 and 4 mag are found.
| Photometry and Classification of Stars Along the Camelopardalis and Perseus Border
Seven-color photometry in the Vilnius system for 309 stars down to 12.5mag in the area along the galactic equator near the Camelopardalis andPerseus border is presented. Photometric spectral and luminosity classesof the stars are determined.
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