Dear friends,
This summer, I worked on an article that describes the results of our 2020–2023 search for narrowband radio signals around nearly 12,000 stars. This paper has been accepted for publication in The Astronomical Journal. There are lots of goodies in the paper beyond our search results. For instance, we quantify the efficiency of radio SETI detection pipelines by injecting 10,000 artificial signals in raw data and identifying the fraction of signals that are actually detected. The UCLA SETI pipeline recovers 94.0% to 98.7% of the injections, depending on the level of radio frequency interference (RFI). Another pipeline that has been used in at least a handful of recent SETI papers did not fare as well, with recovery rates between 6% and 25%, depending on the range of frequency drift rates considered. Pipeline efficiency has a substantial impact on estimates of SETI search volume and transmitter prevalence, but has rarely been considered in the SETI literature to date. In our paper, we encourage the SETI community to incorporate this efficiency in estimates of SETI search volume. For instance, the Drake Figure of Merit is widely used to estimate SETI search volumes and it includes key parameters such as bandwidth, sky coverage, and detectable flux. We proposed a modified formulation that also includes pipeline efficiency as well as the range of frequency drift rates considered, which is another obvious dimension that describes the completeness of a search.
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The modified Drake Figure of Merit quantifies the search volume of radio SETI efforts. Included here are Horowitz and Sagan's 5-year META search, Harp et al.'s 5-year search with the Allen Telescope Array, the Breakthrough Listen searches of 692 (primary) and 1327 (primary) stars, and 2016–2023 UCLA SETI searches.
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We also provide new bounds on transmitter prevalence, i.e., the fraction of stars that host transmitters detectable in our search. On the basis of our results and the GAIA survey, we found that this fraction is less than 0.0003 for stars within 20,000 light years of the Sun. We did not find a clear exposition of this calculation in the recent literature, which is astonishing considering that prevalence estimates are arguably the most tangible results of SETI searches to date. We took care to explain our formalism in detail in the paper. To our surprise, we were unable to reproduce any of the prevalence calculations published in a handful of recent papers, which prompted me to state at a recent meeting of the IAA SETI Permanent Committee: "Either we are doing it wrong, or everybody else is doing it wrong". I encouraged the SETI community to review our formalism and inform us of any deficiencies. Regular UCLA SETI supporter and co-author Larry Lesyna pointed out that, under ideal search conditions, our formalism reduces to an expression published in the Cyclops report edited by Bernard M. Oliver and John Billingham, so we are in pretty good company.
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Our paper describes new and improved upper limits on transmitter prevalence (95% confidence level) as a function of transmitter duty cycle.
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With assistance from graduate students, I will be hosting a Solar Eclipse Viewing Party (free and open to the public) on Saturday, October 14, 2023 from 8:00 am to 11:00 am at the Palisades Recreation Center (Veterans Gardens) in Pacific Palisades, CA. Weather permitting, we will experience a partial eclipse of the Sun, when up to 70% of the surface of the Sun will be obscured by the Moon. We will provide eclipse glasses (while supplies last) and set up a telescope with a solar filter as well as projection telescopes known as Sunspotters. The Sunspotters were gifted to my department by Michael Thacher, who also supports UCLA SETI. I hope you get to see the eclipse (safely), wherever you are.
Warm regards,
Jean-Luc Margot
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