William Mallard

New SETI Sky Surveys for Radio Pulses

Berkeley conducts 7 SETI programs at IR, visible and radio wavelengths. Here we review two of the newest e orts, Astropulse and Fly’s Eye. A variety of possible sources of microsecond to millisecond radio pulses have been suggested in the last several decades, among them such exotic events as evaporating primordial black holes, hyper-flares from neutron stars, emissions from cosmic strings or perhaps extraterrestrial civilizations, but to-date few searches have been conducted capable of detecting them. The recent announcement by Lorimer et al. of the detection of a powerful ( 30 Jy) and highly dispersed ( 375 cm 3 pc) radio pulse in Parkes multi-beam survey data has fueled additional interest in such phenomena. We are carrying out two searches in hopes of finding and characterizing these uS to mS time scale dispersed radio pulses. These two observing programs are orthogonal in search space; the Allen Telescope Array’s (ATA) ”Fly’s Eye” experiment observes a 100 square degree field by pointing each 6m ATA antenna in a di erent direction; by contrast, the Astropulse sky survey at Arecibo is extremely sensitive but has 1/3,000 of the instantaneous sky coverage. Astropulse’s multibeam data is transferred via the internet to the computers of millions of volunteers. These computers perform a coherent de-dispersion analysis faster than the fastest available supercomputers and allow us to resolve pulses as short as 400 nS. Overall, the Astropulse survey will be 30 times more sensitive than the best previous searches. Analysis of results from Astropulse is at a very early stage. The Fly’s Eye was successfully installed at the ATA in December of 2007, and to-date approximately 450 hours of observation has been performed. We have detected three pulsars (B0329+54, B0355+54, B0950+08) and six giant pulses from the Crab pulsar in our diagnostic pointing data. We have not yet detected any other convincing bursts of astronomical origin in our survey data.

Mid-infrared interferometry with high spectral resolution

The Infrared Spatial Interferometer (ISI) is a three telescope interferometer system that operates near 11 microns wavelength using heterodyne detection with CO2 lasers as local oscillators. Stellar measurements have been made using consistent instrumentation for 20 years, allowing comparisons of stellar sizes of red giant and Mira stars over time intervals which are long in comparison to stellar luminosity periods. Recent visibility and closure phase measurements of the star Betelgeuse have been fitted to simple image models and these results have been added to the 17 year record of stellar observations. A new area of investigation of stellar properties at very high spectral resolution will begin in the 2010-2011 observing season. The design of a new digital spectrometer-correlator system is discussed. This system will obtain visibility measurements on-and-off individual spectral lines and the continuum, simultaneously.