Fermilab Dyson sphere searches  updated February 26, 2016  D. Carrigan carrigan@fnal.gov (subject line must be sensible)

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Introduction:
The Fermilab Phase I IRAS filter-based search for Dyson spheres was reported at the International Astronautical Congress in  Vancouver in 2004. Phase II, a more sophisticated search using the IRAS Low Resolution Spectrometer (LRS), has been published (on right). The Phase II technique follows the Dyson Sphere search exercise for amateurs page. IRAS appears below in this NASA-JPL image.

Information contines down the page, click
Typical spectra, Results, Aitoff plot, SETI follow-up 		Links to the Fermilab search:

Particle astrophysics seminar - Fermilab - Jun 2 2008 (pdf)

The Fermilab search has now been published in Astrophysical Journal 698  2075-2086 (2009). It is available at http://stacks.iop.org/0004-637X/698/2075.
IRAS Search constraints:
An ideal instrument for a Dyson sphere study is an all sky survey covering a wide wavelength band centered in the 10 micron regime equivalent to 300 degrees Kelvin. These two requirements were satisfied by the mid-eighties IRAS satellite.  A central mission for IRAS was to study cosmic dust, so there was no premium on resolution and the mirror had only a 0.6 m diameter.  Still, the performance was satisfactory for a Dyson Sphere survey. The sensitivity was 1 Jansky while the angular resolution was 1 minute. Starting from a 250,000 source sample sources were discarded if the IRAS flux quality for the 12 and 25 μm filters only corresponded to an upper limit. This left 10982 sources. The search focused on a temperature range of 100 to 600 °K leaving about 6521 sources. No cut was made on proximity to other sources. By doing this partial Dyson spheres were not ruled out. As noted on the Dyson Sphere look-alike page there are several natural surrogates that are difficult to rule out. Several cuts were used on the LRS sample to focus in on a Dyson Sphere signature. These included temperature, classification, and visual scans in SIMBAD. This led to a sample of 17 weak and ambiguous candidates..
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A SiC emission line - low temp C star

SiC emission line
 Closest "candidate"
closest "candidate"
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Phase I results:
Phase I showed that less than 1 in 600 of the IRAS sources were clustered within about 10% of the blackbody line. During Phase I it became clear the IRAS Low Resolution Spectrometer data with many more points in a spectrum could give more definitive fits. That approach has been pursued in Phase II. 		Phase II results:
Using the Low Resolution Spectrometer yielded 17 ambiguous candidates of which four were slightly amusing but still ambiguous and questionable. The largest one sun bolometric distance in the 17 source sample was 118 pc. The 11000 source Calgary sample extended down to 1-2 Jy which would have given a maximum bolometric distance of 300 pc for LRS sources. This region includes something like a million stars.
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Aitoff plot for IRAS -blue dots several thousand selected sources for investigation. Red - 17 ambiguous Dyson sphere "candidates". Green lines show Arecibo SETI region
Aitoff plot
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Allen H line

SETI follow-up:

More recently Peter Backus of the SETI Institute, Jim Annis and I have been carring out a SETI investigation of some of these lackluster Dyson sphere candidates using the Allen Telescope. Neutral hydrogen, known in radio spectra for many decades, often appears in SETI scans. The panel shows a 2 MHz portion of the spectrum near the famous neutral hydrogen line for the “best” Dyson sphere candidate shown above (IRAS 20369-5131). While it is amusing to think about the shoulder it is due to in all likelihood to a second cloud with a bluer Doppler shift, common in these SETI investigations.