SETI USING INTERFEROMETRIC TECHNIQUES

Abstract

The search for extraterrestrial intelligence (SETI) using radio telescopes and the astronomical technique of very long baseline interferometry (VLBI) emerged at roughly the same time. Radio SETI has however been restricted to single dish antennas and beam-forming arrays and is yet to exploit the full advantages of VLBI. Besides the obvious advantage of being able to localize a potential techno-signature over short time frames, VLBI offers the added advantages of immunity to local radio frequency interference (RFI) which does not correlate and added redundancy in the case of signal detection due to the multiple baselines. To develop SETI techniques using VLBI we made observations of targets in the Kepler field at 21-cm using the European VLBI Network (EVN). Firstly, we selected compact targets with flux densities above 40 mJy from the NRAO VLA Sky Survey (NVSS) in regions of the Kepler field where there is a lack of good calibrators. Then we phase referenced them with known very long baseline array (VLBA) calibrators in the same field. One of the VLBA calibrators, J1926+4441, lies about 1.88′ from Kepler-111, a G-type star that hosts Kepler111-b which is an "Earth-like" exoplanet. We then correlated the data in two passes; in the first pass, all the data were correlated at 32 frequency channels over an 8 MHz bandwidth and 2 seconds of integration in time. In the second pass, the data for the observing scans of J1926+4441 were correlated at 16384 frequency channels over the same bandwidth and 0.25 seconds integration in time. This preserved a large field of view encompassing Kepler-111b allowing for phase rotation of the data to the location of the exoplanet for technosignature search. The precise targeting of the exoplanet is aided by proper motions from GAIA and distance measurements from the Bailer-Jones catalogue. We map all the targets from NVSS but fail to make detections above 5ð. The cause of this remains unclear. During the analysis of the high-resolution data, we encountered a feature in the autocorrelations and cross-correlations and by querying existing surveys of galactic hydrogen we prove that the feature in the former is due to the emission of neutral galactic hydrogen. However, the feature in the cross-correlations eludes explanation, as galactic hydrogen cannot correlate at VLBI baselines due to its low brightness temperatures. Nonetheless, through a follow-up observation using the e-MERLIN, we judge the data adequate, flag the feature and proceed to search for technosignatures from the Kepler-111b. We make image cubes and search for signals with a drift rate up to 2 Hz/s that have signal-to-noise ratios exceeding 5. We also fail to detect any such signal, but constrain the power expected from a receiver on the surface of Kepler-111b to ∼ 3.75 × 1015 watts.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Garrett (Supervisor) & Jack Radcliffe (Supervisor)