# Presentation: 183789

## Search for Dyson Spheres using the IRAS catalog

**Dick Carrigan**
**Fermilab**

- Infrared Processing and Analysis Center, Caltech/JPL.
- IPAC is NASA's Infrared Astrophysics Data Center.

**Notes:**
Good morning. I am Dick Carrigan. Today I’m going to talk about searching for so-called Dyson spheres using the database from the IRAS satellite shown on the left. Dyson spheres were suggested by Freeman Dyson many years ago. The idea is that an advanced civilization could break up the planets around a star to form a spherical cloud or “shell” that would absorb most of the light coming from the sun and thereby harvest more of the star’s energy.

## Marching plan

**Searching for signs of life, extraterrestrial intelligence**
**The Dyson Sphere conjecture**
**IRAS and other infrared instruments **
**Dyson Sphere search scheme **
**Illustrative sources including mimics **
**Results, and other searches**
**Future possibilities? **

**Notes:**
First I will review signatures for life and extraterrestrial intelligence then go on to the Dyson Sphere conjecture. Next I will consider the capabilities of IRAS and other infrared telescopes as Dyson Sphere detectors including the specifics of the IRAS search scheme. I will go over the spectroscopic information for several sources including Dyson Sphere mimics and some interesting and less interesting candidates. I’ll summarize the results and compare them to other investigations and SETI searches. Finally I’ll look at possibilities for the future.

## THE RADIO SETI PARADIGM

- SETI radio beacon (acquisition signal) –but why?

- Material and electromagnetic
- artifacts like a Dyson Sphere don’t require reason to communicate

- A substantial fraction of  sun-like stars out to several hundred light years have been monitored for ETI with radio SETI.

- Stat Mus-Berlin

- Arecibo via satellite

**Notes:**
Interest in searching for signs of life beyond the earth is quickening. The principal scientific thrust is to look for biological signatures. A second approach is to search for signs of extraterrestrial intelligence. This program is called SETI. Note that there is a distinction here, life can include some very simple forms while intelligence might just possibly transcend life, say cell phones gone wild. The current SETI paradigm is heavily dependent on the presumption that the originating civilization will provide a beacon, much in the spirit of lighthouses indicating coast lines. The problem here is understanding just why a civilization would bother. My own view is that most of the justifications would be unfavorable to the receiving civilizations. By now radio SETI has checked stars out to several hundred light years with no sign of a signal. 
A different approach is to look for material and electromagnetic artifacts of advanced civilizations like Dyson Spheres. These correspond to objects like the pottery shards, garbage dumps, or pyramids that are the messages of archaeology. Most of these archaeological signals were not intended as messages to the future. They did not require a conscious decision to try to communicate Evidence of some cosmic archaeological artifact does not require an intent to communicate. The situation is similar to this 3400 year old bust of Neferititi that gives some insight into ancient Egypt. The Neferititi bust is equivalent to an artifact signal to us from a star one fifth of the way to the center of the galaxy.

.

. 

## COSMIC ARCHAEOLOGY (CA)

**COSMIC ARCHAEOLOGY (CA)**

**SETI**

**Radioactive waste disposal in a star **** – Type I**

- G. Lemarchand**, **SETIQuest, Volume 1, Number 1, p. 3.** **
**     **On the web at http://www.coseti.org/lemarch1.htm

**Kardashev civilizations****:**
** **
**	****I-planet  (10****16**** W) your world now: 10****13**** W**
**	****II-star  (4*10****26**** W for sun)  -Dyson Sphere**
**	****III-galaxy (10****36**** W)  -- ****Jim Annis**** search**

**Stellar engineering ****– Type II – M. Beech’s book**

**Extrasolar planetary atmospheres ****-Type I**

**Notes:**
There are many possibilities for cosmic archaeological signals. One of the more interesting perspectives on the cosmic archaeology question is a classification scheme suggested by Kardashev. He divided civilizations into those harvesting all the energy of a planet, of a star, and of a galaxy. A Dyson Sphere would be a type II Kardashev civilization. Jim Annis, an astronomer at Fermilab, has looked for type III Kardashev civilizations by plotting a surrogate for the galaxy brightness versus the size of the galaxy for a million elliptical galaxies. This distribution follows the Tully-Fisher relation. Most of the galaxies lie close to the line. The outlier line is 1.5 magnitudes higher (representing a 75% dimunition of the light output). No galaxies reach the outlier suggesting that there are few 75% efficient type III Kardashev civilizations. Another signal suggested by Drake and Shklovski is the appearance of unusual spectral lines such as Technetium in a star due to purposeful salting of the star. They estimate that it would require 105 tons to produce a recognizable signature. Nuclear waste disposal to the surface of a star might produce a similar signal.  Other signatures might arise from trying to manage the life cycle of a star across the Hertzsprung-Russell Diagram. A recently published book by Martin Beech discusses some of these possibilities. Finally, there is the possibility of Dyson Spheres.

## AN EXAMPLE OF CA: DYSON SPHERES

-     “loose collection or swarm of objects
-     traveling on independent orbits...”

- Searches-problem fixing distance.
-    Earlier-Sylsh, TKP, Jugaku, ...

- Signature
-     infrared
-     stellar luminosity (distance problem)
-     pure Planck
-     no star for pure DS

- Types of Dyson Spheres - ...pure, partial, rings,

**AN EXAMPLE OF CA: ****DYSON SPHERES**

- Based on G. Lemarchand

- Types
-     pure – star completely obscured
-     partial

- Sagan and Walker, Astrophysical Journal **144(3)**, 1216 (1966)
-     search feasible even with sixties technology but that the possible confusion
-     with natural signatures could require searches for other artifacts of intelligence

**Notes:**
In 1960 Dyson suggested that a society growing modestly would soon outrun its planet based energy resources. He suggested creating a loose collection or swarm of objects in a spherical cloud around the star to harvest the energy. The material thickness would be on the order of a centimeter.  This is thick enough to adsorb all  the visible light. The spherical swarm would radiate the energy away at a temperature of about 300 degrees Kelvin. Dyson spheres could come in several varieties. A pure Dyson Sphere would contain all of the visible energy of the star so that no visible star would be present. A partial Dyson Sphere would only partly cover the star. This could occur for something like a ring distribution or because the overall density was such that there was not total obscuration. A partial Dyson Sphere would be an easier object to build. The signature for a Dyson sphere is a strong infrared signal with the luminosity of a normal star. There have already been several Dyson Sphere searches. I will come back to them later. As far back as 1966 Sagan and Walker showed that that Dyson Spheres could be detected out to 1000 parsecs with sixties technology. They did note that there would be a problem with confusion with natural signals and suggested that SETI searches could be used to sort out the problem.

## Dyson Sphere engineering

- Scale of a Dyson Sphere
**Jupiter-scale Dyson Sphere 2*10**27** kg**
**Earth’s biosphere 10**15** – 10**16** kg**
**Great Wall of China 10**12** kg**
**International Space Station weighs 2*10**5** kg, ocean liner 1.5*10**8** kg**
- Energy cost to build?
**800 years of ****total**** solar radiation, not amount falling on planet’s surface. **
**	****(The 800 year number is of the order of the gravitational energy of Jupiter.) **
**Poses a bootstrap problem**
- Is a Dyson Sphere rigid?
**Dyson - swarm of objects**
**Papagiannis: rigid shell for gravitational case alone ****unstable**
- Stability of a Dyson Sphere swarm?
**stability of elliptic and spiral galaxies **
**	****planetary formation in the solar system**
**actively steered, perhaps by solar sails**

**Notes:**
The mass of a Jupiter-scale Dyson Sphere would be 2*1027 kilograms. Earth’s biosphere is estimated to be in the 1015 – 1016 kilogram range. The largest ocean liner is 1.5*108 kilograms while the immobile Great Wall of China is on the order of 1012 kilograms and took 2500 years to build. The International Space Station weighs 2*105 kilograms so that it is a factor of ten billion trillion smaller than a Jupiter-class Dyson Sphere. In short, a Dyson Sphere is a large object! Dyson’s perspective on this was to note that increases of scale such as this can be reached in 3000 to 4000 years based on a population growth of O(1%/year). 
The energy cost of constructing a Dyson Sphere is high. Dyson notes that the energy to disassemble and rearrange a Jupiter size planet is equivalent to 800 years of total solar radiation, not the much smaller amount of solar radiation falling on the planet’s surface. (The 800 year number is of the order of the gravitational self energy of Jupiter.) This poses a bootstrap problem in the building process. Initially the available power would be low but would rise as more surface area developed. In any case the construction time would probably be much longer than 103 years. For scale, Earth-based projects such as cathedral or military fortification construction like the Great Wall of China have required times of 102 to 103 years. Mass loss time scales for circumstellar dust clouds can be in the 103 to 105 year range. Creation of these clouds requires a significant part of the stellar energy.
One of the criticisms of Dyson’s proposal from the start has been based on the incorrect presumption that Dyson’s object was a rigid, hollow sphere. Papagiannis has given a convincing calculation showing that a rigid spherical shell could not be built if only gravitational force is considered (that is, neglecting radiation pressure and centripetal effects). He then goes on to argue that a system of “space structures” would only obscure 1% of the light from the star. This is the justification used for partial searches such as those of Jugaku. This argument would seem to ignore a shroud consisting principally of thin silicon chips, solar panels, or carbon nanotubes. Put differently, it is difficult to anticipate the size or the technology going in to the individual cells in a Dyson Shroud developed by an advanced intelligence.
Another criticism of the Dyson hypothesis says that a spherical shroud is not a stable system. Somewhat similar systems are studied in connection with the stability of elliptic and spiral galaxies as well as in connection with planetary formation in the solar system. Presumably if instabilities develop in a rotating Dyson Sphere it could collapse to a disk under its own gravitational attraction. On the other hand the individual cells in the shell could be actively steered, perhaps by solar sails. 

## But some other objects act sort of like a Dyson Sphere

- From p. 14 of May, 2008 Physics Today
- 	reporting on Spitzer IR results on water vapor in regions where terrestrial planets form
-  	(artist rendition supplied by Robert Hurt, NASA/JPL-Caltech)

**50 AU**

**T = 170****oK**

**Notes:**
Several natural astronomical objects can mimic a Dyson Sphere. This artist visualization shows a dust and water vapor cloud forming a protoplanetary disk. Spitzer has recently provided IR data on a similar situation. Notice how the star is partially obscured. This system is large compared to our expectations for a Dyson Sphere. The swarm for a Dyson Sphere would have a radius on the order of 1 AU.

## DYSON SPHERE SURROGATES

**DYSON SPHERE SURROGATES**

- Brown dwarfs but temperature is typically higher
-     absolute luminosity is lower. **Not candidate**.

- Stars are born and die in clouds of dust

**Notes:**
Here are a number of Dyson Sphere surrogates. Planetary nebula might be confused with Dyson Spheres with temperatures in the 200 oK region.
Other possibilities include late type stars with shells such as C stars or “Miras” variables.  Very thick dust clouds occur when there is an extreme phase of mass loss. Since this is a fast process these are apparently rare. In addition for a thick cloud of dust one sees an agglomeration of blackbody spectra for many different temperatures.
Very young stars or protostars are typically in situations where there is a lot of dust and a lot of star formation. An example is Orion.
Brown dwarf temperatures are generally higher than those expected for Dyson Spheres. The luminosities are also expected to be lower.

## IRAS

**Notes:**
An ideal instrument for a Dyson sphere study is an all sky survey, like the ground based 2MASS project. The detectors should be sensitive to infrared over a wide wavelength band centered in the 10 micron regime. This corresponds to the 300 degree Kelvin temperature range. These two requirements narrow the choice to the IRAS satellite that flew in the mid-eighties. IRAS had filters at 12, 25, 60, and 100 microns. A central purpose was to study cosmic dust. As a result there was no premium on resolution and the mirror had a diameter of 0.6 m.  Still, the performance was quite satisfactory for an initial Dyson Sphere all sky survey. The sensitivity was in the 0.5 to 1 Jansky range while the angular resolution was on the order of 1 minute. Two hundred fifty thousand point sources were identified. The data base is widely available and quite comprehensive. The ground based 2MASS survey contains several thousand times more sources with much better resolution. It is of limited use for a Dyson Sphere survey because a 300 degree Kelvin source must be twenty times the IRAS minimum in the 12 micron filter to register in the 2MASS 2.17 micron filter.

## Infrared resources and databases

- Other resources include MSX (fills in IRAS dead region), DIRBE (on COBE), Gemini (S. Allam: earth-based including spectroscopy), AKARI satellite, NICMOS (Hubble), and Spitzer

**Notes:**
Currently there are many other sources for infrared information in addition to IRAS and 2MASS. MSX, the Starwars Midcourse Space Explorer satellite intended to fill in IRAS gaps has useful filter information. DIRBE on COBE has IR filter information but with poor spatial resolution. The ground based Gemini pair of telescopes can provide high resolution spectroscopy for individual sources. The Japanese satellite Akari has flown but I have not been able to get at the data. NICMOS on Hubble has good spectroscopy  for individual sources. Spitzer is in operation but no new proposals are possible. The spectroscopy is good but the filters, intended for Polycyclic Aromatic Hydrocarbon (PAH) are at relatively short wavelengths. The curve shows a real room temperature source as seen in IRAS.

## First search with filters –Planck fit with three filters(R. Carrigan, IAC-04-IAA-1.1.1.06, 55th IAC 2004) (IRAS 06176-1036 “Red Rectangle”)

- F is IRAS flux, K is Planck color correction,
- P is Planck dist., sigma is weight,
- a is fit parameter, k is filter index, m is temp
- index, and n is source index

- But look out!
-     IRAS has problems with Cirrus and
-     Zodiacal dust in the
-     60, 100 μm filters

**Notes:**
Two approaches were used in the first phase of this investigation to determine the putative temperature and temperature deviation for a fit to the three filters. The first formed a weighted least squares for  an array of temperatures from 150 to 500 degrees Kelvin in 50 degree increments for the roughly twenty thousand sources. In the formula F is an IRAS flux, K is an IRAS Planck color correction, P is the Planck distribution at the filter “center”, sigma is a weight, and a is the fitting parameter (related to the luminosity). The minimum of this distribution was identified from the array and this was used to refit the Planck distribution. The distribution shown here is the case for a bright planetary nebula called the “Red Rectangle.” This is a well studied object and is not a Dyson Sphere. The diamonds show the IRAS filter values. Note that the 100 micron filter is not riding high here. The position of the 2MASS filter is shown in green. Note that the Planck contribution at 2.2 microns is very small. As noted earlier, IRAS often saw Cirrus and Zodiacal dust in the 60 and 100 micron filters.

## Calgary atlas – 11224 sources

FQUAL(12), FQUAL(25) > 1

- FQUAL(12), FQUAL(25) > 1

**SEARCH WITH IRAS LOW RESOLUTION SPECTROMETER**

**Notes:**
Calgary has prepared a database of more than 11000 IRAS LRS spectra, roughly double the number in the original IRAS release. They have classified each source according to this table. After a preliminary scan of several hundred random sources it was clear that Dyson Sphere-like candidates fell in the C, F, H, and U categories. C includes carbon stars, F are featureless spectra, H are typically hydrogen clouds, etc, and U are unusual objects. Later I also included P objects with red continua and a sharp blue rise. Later still P was discarded again. To avoid dust problems with the 60 and 100 micron filters I used the color-color temperature curve shown here based on the 12 nad 25 micron filters to select ”low” temperature objects in the 100 to 600 degree Kelvin range.

## Source flow through cuts

- (no source or stellar association in catalogs)
- Fit to Planck distribution

- Visually scanned for:
-      non-Planck shapes
-      obvious spectral lines
-      large data scatter
-      visible stars with something else
-      identification of the source
-           with a known object

**Notes:**
With quality factor, temperature, and category cuts the search was narrowed to several thousand sources. In the next stage the search was originally limited to pure Dyson spheres in part by selecting on the IRAS IDTYPE variable for no catalog sources (0). It became apparent that this could be extended easily to partial Dyson Spheres by including stellar catalog cases (2). Finally I realized I should have also included multiple catalog cases and “other”. As a result the only  class I ended up excluding was extragalactic objects (1) leaving a sample of about 1500 sources. These sources were directly scanned for spectral lines, clear classifications as conventional objects, large data scatter, and visible stars with another plausible identification. This left a sample of 65 sources.

## FITTING TO A PLANCK DISTRIBUTION

**FITTING TO A PLANCK DISTRIBUTION**

**Notes:**
Least squares tests were introduced for the next stage by fitting the LRS data to a Planck distribution that is a function of the amplitude and the temperature. The distribution of the LRS points is a function of many factors including the possibility of non-stellar lines, non-Planck and multi-Planck aspects, source variability in many cases, and differences between the long and short wavelength parts of the spectrometer. In that sense the fit is as much a screen as a statistical measure. The weighted least squares was used to eliminate sources above 0.25 and a few more > 0.19 associated some other reasonable identification or very bright 2MASS object. This process left seventeen interesting sources of which four had rather better fits. However each of these sources had some sort of flaw or uncertainty. The following slides review some of these objects and pseudo Dyson Sphere candidates. 

## SOME PARTIAL MIMICS

**SOME PARTIAL MIMICS**

- Illustrates a common case, an 11.3 μm SiC emission feature typical of C stars. Often the background is a BB spectrum. Notice the 2MASS points on BB distribution. Line is not a natural DS feature. IRAS IVAR is 99%.
- T = 594 oK (with line), no visible star.
- (Scale: F(Jy) = y axis/0.0046)
- F[12], etc are temperature color corrected

- Shows a 10 μm absorption feature that sometimes occurs in OH/IR stars. SIMBAD classifies it as a star with an OH/IR envelope. T = 246 oK (with line),
- no visible star.
- (Scale: F(Jy) = y axis/0.0103)

- LRS short + , long – dots,
- filters – diamonds, 2MASS - triangles
- dotted curve - fit to 12, 25, 60 filters,
- LRS Planck distribution fit - solid curve.

**Notes:**
The left hand panel shows a common signature for a low temperature carbon star with an 11.3 micron silicon carbide line. The LRS points are shown as plus signs for the short wavelengths, dots for the longer ones. The diamonds are the IRAS filters. The dotted line is a fit to the 12, 25, and 60 micron filters. The solid line is the LRS fit. Notice that the 2MASS points lie on the curve. There is a distinct difference between the filters and the LRS. This is in line with fact that the IRAS IVAR index is 99%. This is a source that is barely inside the upper temperature bound. The scale factor can be used to scale the y axis to Janskys. The right hand panel illustrates another mimic due to sources with hydroxyl masers (OH/IR). These can have a 10 micron absorption feature. Both of these lines are more than 10 sigma above the “background”. Evidence for lines could be picked out down to about the 2 sigma level. [156826, 212309 Figures 1, 2 (p. 10).]

## ANOTHER MIMIC

**ANOTHER MIMIC**

- Looks like a Planck spectrum but has another explanation. Calgary classifies it as H. It may be near an HII region. Typically these H sources have low temperatures.
- T = 132 oK, source near a visible star
- (Scale: F(Jy) = y axis/0.0051)

**Notes:**
This spectrum illustrates another mimic due to a Calgary H case. The sources are often rather good black body fits but with temperatures that are typically below 200 degrees Kelvin. These sources were ruled out. [96506, Figure 3 (p. 11)]

## Closest “candidate”, one of best fits

**SIMBAD says C star but Calgary gives U**
-         can’t find classification literature
-         may be  based on millimeter region
- Open circles – DIRBE but may be second
-         source, open squares - MSX
- T = 376 oK, no visible star
- (Scale: F(Jy) = y axis/0.0168)

**Notes:**
Now for some of the more interesting cases. This source is one of the best fits. The temperature is around the boiling point of water and there is no visible star. SIMBAD, the Strasbourg database, classifies this as a carbon star while Calgary classifies it as U. I was not able to untangle the basis of the SIMBAD classification. This illustrates a case where one could out of hand discard the source as a Dyson Sphere but the evidence is ambiguous. Indeed the SIMBAD classification might have been only on the basis of IR color-color. Another problem for the source as a Dyson Sphere candidate is the DIRBE information. That information conflicts with the MSX information. Could it be that the DIRBE low angular resolution data is associated with another source? [222772]

## Distance estimates

- D is source distance (kpc)
- L, Lo are luminosities of putative DS and Sun. Distance

- Slysh peak flux formula

- Possibilities:
- proper motion (2/17)
-      visible star (10/17)
- red shift via
-       maser signal or
-       binary companion.
- galactic scale height for
-      rough limit
- bolometric

- Partial (nearer)

**Notes:**
Some sort of a distance estimate is necessary to untangle whether an IR object is radiating in the regime of a sun-like star. Possibilities include proper motion or sensitive Doppler information either from a binary companion, a visible star in a partial Dyson Sphere situation, or a maser. The parenthetical cases indicate the fractions of these for the 17 source sample. I have also looked at a galactic scale height to argue a rough upper bound on distance. This is obviously fraught with problems. In his search with and early IRAS data release Slysh developed a bolometric formula for the peak flux. This can be inverted to get a one sun bolometric distance for a pure Dyson Sphere. The formula can be applied to partial Dyson Spheres by including the fractional area covered by the “sphere”. Clearly partial cases have to be nearer than their fully shrouded twins to give the same peak flux.

## Closest “candidate” - continued

- D(1 sun)bol = 42 pc
- Dscl(galactic) is O(2000pc)

**Notes:**
For this case the 1 sun, pure Dyson Sphere bolometric distance is 42 pc. The very rough scale height distance is several thousand pc. It implies a luminosity several thousand times the solar luminosity.

## 
source region was observed with the Arecibo telescope in the SETI SERENDIP program (later slide)
No SETI detection .

- source region was observed with the Arecibo telescope in the SETI SERENDIP program (later slide)
- No SETI detection .

**wide discrepancy** between filters, MSX, spectrometer
- variability 99%
- F[100] filter is 10-20 > low filters
- temperature is low, 208 oK
-     **H rather than U?**
- one sun bolometric distance is 34 pc
- (Scale: F(Jy) = y axis/0.0563)

- Another good fit

**Notes:**
Here is another low least squares source. The right hand graph extends out to the 100 micron filter. Notice that there is a very large difference between the filters and the LRS in addition to a high variability. This event is strikingly similar to the H event shown earlier. A good case can probably be made that it is misclassified in the Calgary LRS database. This source was within the region covered by the SETI SERENDIP search. That source saw no SETI signals. [Fig 5 198730]

## Two other low least squares fits

- Classified U but maybe H?
- Hint of structure at 8 μm
- T = 177 oK
- Note F[60], F[100] filters high,
-    suggests an even lower temperature. The bolometric distance is 45 pc
- (Scale: F(Jy) = y axis/0.0055)

- T = 538 oK
- DIRBE suggests higher temperature
- 13.5 μm emission artifact?
- bolometric distance is 55 pc
- (Scale: F(Jy) = y axis/0.0425)

**Notes:**
This slide shows the other two low least squares cases. Again, while Calgary classifies the source on the left as “U” it looks more like the two H cases and the temperature is a lower 177 degrees Kelvin. A fit to all four filters would give an even low temperature. On the other hand IVAR = 0%. The right hand panel shows a source classified as F by Calgary. The 2MASS points match up with the LRS Planck fit. In this case a polynomial fit is about as good as a blackbody distribution. There is nothing reported for MSX. Several filter points from DIRBE are shown as open circles. They suggest a blackbody distribution that extends below the LRS wavelengths. The fitted blackbody temperature is 538 oK. There is a hint of an emission artifact at 13.5 μm and a weak visible star. The source is in the direction of the galactic center but above the galactic plane. There is an indication of variability. With the available information it would be hard to make a case that this source is an interesting example of a possible Dyson Sphere candidate. The one solar bolometric distance is Dbol = 55 pc.  [221999, 133377]

## ANOTHER NEAR CANDIDATE

- Planck spectrum? Polynomial better. Scatter high. This is the problem when deviations become larger. Kerton and Brunt - no CO associations for this source.
- Calgary F
- T = 381 oK, apparently no visible star.
- (Scale: F(Jy) = y axis/0.0541)

**Notes:**
Here is one more near candidate. This could be a Planck spectrum but the scatter is high. The unweighted least squares is 0.163. This illustrates why it becomes difficult to identify a Dyson Sphere signature as the least squares fit value increases. [15762 Figure 7 (p. 11)]

## Summary slide – 17 sources

**Notes:**
Sorry about this table, it is mainly for my personal reference for the 17 sources. The difference between the four most interesting sources and the others can be seen in the unLSQ column. Notice that this table contains only U and F sources. About half of them are associated with visible stars. Many of the sources exhibit variability. The other point to make is that there is quite a bit of information now on all of these sources.

## Reach of search

- Largest Dsol (17 source sample) =  **118 pc** (Sm = 8.6 Jy)
- For 65 source sample: F > 4 Jy
- 	then could have Dsol ~150 pc
- 	LRS: down to ~ 1-2 Janskys in 11000 source sample
- 	Could have found Sun-sized Dyson Spheres out to **300 pc**
- 	**O(1 M) solar type stars**
- For galactic disk scale height of 100-200 pc
- 	(and assuming one solar luminosity estimate ~150 pc)
- 	then this IRAS LRS sample would be scattered over the whole sky
- 		rather than lying near the galactic plane
- Actually  **1/4 scattered over whole sky**
- 	other 3/4 in galactic plane
- 	These sources are probably more luminous and at greater distances.

**Notes:**
The largest bolometric distance in the 17 source sample is 118 pc. This was for a maximum peak flux of 8.6 Jy.  The smallest maximum peak flux in the 65 source sample was about 4 Jy. For that level the search could have reached out to 150 pc. The 11000 source sample extended down to 1-2 Jy which would have given a maximum bolometric distance of 300 pc. This region includes something like a million stars. For a galactic scale height of 100-200 pc the 65 source bolometric distance of 150 pc suggests the sources would be scattered over the whole sky rather than lying near the galactic plane. As seen in the next transparency only one quarter of the sources are scattered over the sky suggesting that most of the sources are at greater distances and are more luminous.

## WHERE ARE THE INTERESTING SOURCES?

- 2240 event sample
-      follows galaxy,
-      although less
-           in core?
- 17 interesting events
-      Some away
-          from plane
-      (meaning nearer?)
-      biased to left side

- Pleiades

- Galactic center

**Notes:**
Here is the distribution of the seventeen source set over the sky in terms of galactic coordinates. The bias to the galactic plane is clear. The dots show the 2240 LRS sample that was selected on temperature and Calgary class. This is also biased to the galactic plane but shows no galactic center bulge. This suggests that the LRS does not reach all the way into the galactic center 8000 pc away. The seventeen source sample has a clear bias to the left side of the Aitoff distribution.

## EARLIER SEARCHES (typically for partial Dyson Spheres)

- Jugaku and Nishimura, *Bioastronomy 2002: Life Among the Stars*,
-     Norris and Stootman, eds, IAU Symposium, **213**, 437 (2002) and earlier
- use the **2.2 μm K band as an indicator** of the photospheric radiation **hosting partial DS**
- then look for an infrared **excess in the IRAS infrared satellite 12 μm** band
-       1 mag difference for 1% sphere. See less than 0.3 mag for 384 stars inside 25 pc.

- Slysh, in *The Search for Extraterrestrial Life: Recent Developments*,  Papagiannis (Ed) 1985. Timofeev, Kardashev, and Promyslov, AAJournal, **46**, 655 (2000) [TKP]
-     _**Four filter IRAS**_ Planck fit. Several candidates, limited sky. 100, 300 °K. 98 stars

- Conroy and Werthimer, preprint (2003)
- Jugaku technique to **older stars**. 1000 nearby older stars from Wright and Marcy        Older stars eliminate dust clouds around young stars. Also planet hosts. Correlate with the K band near-infrared data from 2MASS. **For partial Dyson Spheres**
-     33 in the IRAS 12 μm with 3 σ excesses from mean. About 1⁄2 LRS. None in 17.

- Globus, Backman, and Witteborn, preprint (2003)
-     **temperature/luminosity anomaly** due to the fact that the luminosity of a star
-        surrounded by a **partial DS** would be lowered compared to naked star with same T

**Notes:**
A number of Dyson Sphere searches have been carried out in the past. Jugaku and his colleagues have had a continuing program to use the 2.2 micron K band as an indicator of photospheric radiation and then look for an excess in the 12 micron IRAS band. This presupposes a partial Dyson sphere. A 1 magnitude difference could arise for a sphere absorbing 1% of the stellar light. The measured differences are less than 0.3 magnitudes. Looking at 378 of the 458 stars with infrared excesses within 25 pc of the sun they have found no cases of reasonable partial Dyson Sphere candidates. They do note a few interesting sources. Conroy and Werthimer applied Jugaku’s technique to 1000 older stars that might host planets, partly in the hope that this would eliminate dust clouds around young stars. They did find 33 cases. About half had LRS spectra but none were in the 17 source sample. Globus, Backman, and Witteborn have looked for a temperature/luminosity anomaly in the same spirit as the Annis search for type III Kardashev civilizations. Up to this point they have reported a data set that requires more investigation.

## Reprise on Slysh and Timofeev, Kardashev, and Promyslov (TKP) 

**TKP** lists 14 sources - only six have LRS spectra
- 	(Calgary classifications would have excluded )
- 	for 5 of 6 with LRS data TLRS differed from T4filt differed by average of 110 oK
- 		(LRS temperatures all higher - filter temperatures can be misleading)
- 		2 of the 6 have FQ[12] values of 1 which would also have excluded
- 		Most associated with definite stellar types.
**Slysh** - four out of six had LRS information - 1 in 1527 source sample
- 	IRAS 04530+4427 (Slysh 0453+444) - carbon star (CGCS 6092)
- 		12 μm emission line
- 	IRAS 05073+5248 (Slysh 0507+528) - NV Aur, Mira Cet has an OH/IR maser
- 		excluded from the 1527 source set because of E classification
- 	IRAS 05361+4644 (Slysh 0536+467) - carbon star BD+46 1033
- 		12 μm peak - classified as E by Calgary and therefore excluded
- 	IRAS 17411-3154 (Slysh G 357.3-1.3) - strong absorption feature at 10 μm
- 		it was classified A by Calgary and excluded
- For four with LRS data TLRS differ from T4filt the four filter by average of 44 oK
- 	(the LRS temperatures are all higher).
**No Slysh or TKM included here, 1 in 1527 sample. LRS is an effective tool**

**Notes:**
Timofeev and colleagues (TKP) used early IRAS data to look at sources near the poles, possibly to avoid Zodiacal light confusion. They looked at 98 sources with IR temperatures in the 100 and 300 degree K range and fit a Planck spectrum to the four IRAS filters. Outside of the fact that the sample is limited by the temperature and polar cuts there is another problem with this approach. The IRAS 100 micron filter is sensitive to galactic cirrus so the 100 micron filter often rides high. Six of the 14 sources they discuss have LRS spectra. Most of these are now associated with definite stellar types. Interestingly the filter fits are typically 100 degrees Kelvin lower than the LRS fits. Calgary classifications would exclude all of these. For Sylsh four of the six sources identified had LRS spectra. All four had non-accepted Calgary classifications. Only one of the sources identified in these two experiments were in the 1527 source temperature, class, and Calgary type selected sample. This indicates that the LRS was an effective discriminant for the search compared to the filters. Again all the filter temperatures were low compared to the LRS temperatures.

## Can Spitzer, 2MASS be used? AKARI? Gemini?

- For IRAS filter values in 1-2 Jy regime could fit to IRAC
- 	get up to 300 oK
- Limited to galactic plane for GLIMPSE (80 K IRAS sources)
- Does not extend reach much for 300 oK (factors of 2)

**Notes:**
Could Dyson Sphere searches be extended and would it do any good? Spitzer sensitivities, angular resolutions, and spectroscopy are very good. On the other hand most of the Spitzer program has been concentrated on individual sources. Spitzer’s GLIMPSE program is an important exception. Using the four IRAC filters it has done a continuous photometry study of the galactic plane so it covers about 1/3 of the IR sources seen in IRAS. As seen in the figure, IRAC does not really reach to the 300 degree Kelvin regime. If IRAC, 2MASS and the IRAS filters were coupled into a fitting program it might to study 80,000 sources or about eight times more than with LRS alone. On the other hand the IRAS sensitivity would not be improved. At best the reach might improve by 2-4. On the other hand, Gemini spectroscopy could be used to see if it can rule out members of the seventeen source sample (this was suggested by Sahar Allam). New Spitzer spectroscopy data releases could also be used. This is illustrated in the next transparency.

## Spitzer spectroscopy for IRAS 11544-6408

- Spitzer release from April 15, 2008 (Garcia-Lario et al.)
- Spectroscopy intermediate between MSX, LRS. IVAR =0%?
- Shape shows non-Planck features

- Blue dots-Spitzer

**Notes:**
This recent Spitzer spectrometer data shows how more subtle spectroscopy features can be detected and thereby rule out a fairly good Planck spectrum. SIMBAD classifies this as a post AGB star. It may be a planetary nebula.  

## SETI compare

**SERENDIP** Berkeley (SETI@home)
- 	collected data in Arecibo side lobe
- 	     continuous survey measurements.
- 	angular coverage like Phoenix but uniform
- 	loss of  order of magnitude in sensitivity
- 	     compared to Phoenix
- 	Sampled over ~1 Hz in 100 MHz
- 	     around 21 cm
- 	3 of 17 sources in SERENDIP region
- 	No signals found in SERENDIP
**	****--so that 3 of 17 interesting IRAS sources free of SETI signatures**

**Phoenix**  Arecibo 300 m, Green Bank, ..
- 	O(1000) targets < 250 light years
- 	     (F, G (Sun-like) and K stars) [life]
- 	A region from -2o to +38o declination
- 	sensitivity of O(1 Jy)
- 	“point and shoot”.
- 	1.2 to 3 GHz (includes 21 cm
- 	     hydrogen line)
- 	**No ETI signals detected**
- 	None of 17 sources in Phoenix target list

**Notes:**
Are there sources in the seventeen source sample that have been searched for SETI  signals? The green lines show the Arecibo telescope region accessible to the Phoenix and SERENDIP SETI searches. Phoenix has targeted about 1000 stars for searches over a wide frequency range. The sensitivity of the search is 1 Jy. None of the 17 sources was in the SETI search list. This is not surprising because the SETI list were based on old, visible stars expected to typically harbor planets. This does not directly overlap the effective Dyson Sphere criteria. In any case no ETI signals have been observed in Phoenix. SERENDIP collected data in a side lobe of the main Arecibo beam. As a result they had full sky coverage over the Arecibo portion of the sky but the sensitivity was down by an order of magnitude compared to Phoenix. They also searched a narrower frequency range. Three of the seventeen source set were in the Arecibo region so roughly 15 % of the sample has been searched for SETI signals. SERENDIP also did not find any SETI signatures.

## Allen Telescope Array

- Allen Telescope is a distributed array (about 42 dishes, 350 when complete in 2011) coming on line for SETI in Northern California,
- 	Advantages: 1) wide field of view, 2) frequency 0.5 to 11.2 GHz , 3) multiple back ends, 4) active interference mitigation
- Carrigan, Annis, Backus (SETI Institute) proposal
- 	Concept – look for SETI signals from 17 interesting sources
- 	also look for hydroxyl masers (1612-1720 MHz) to see if they can be used to rule out some sources

- (Credit: Allen Telescope)

**Notes:**
It could be interesting to look at the 17 source sample more carefully for SETI signals. An early 42 dish embodiment of the planned 300 dish Allen Telescope has now come on line. It will be used principally for SETI studies although other radio astronomy work will also be scheduled. The Allen Telescope has the advantage of a wide field of view, a wide frequency span, the ability to use multiple back ends, and active interference mitigation. Jim Annis, Peter Backus of the SETI Institute, and I have recently submitted a proposal to observe the sample. We also hope to look at a test case of a known OH/IR hydroxyl maser to study the capability of the telescope to rule out sources based on maser signals.

## Can the IRAS data accumulated for the Dyson Sphere searchbe used for something else?

- Have an interesting collection of C stars with lines
- Variability of dust shells
- Some IR stars which appear to be misclassified

- Some recent studies:
-  M. Busso, et al., AJ **133**, 2310(2007)
- infrared photometry of AGBs
- J. Rodmann, et al., A&A **446**, 211 (2006)
- large dust particles in disks
- P. Whitelock, et al., MNRAS **369**, 751 (2006)
- photometry on C stars
- R. Szczerba et al., A&A **469**, 799 (2007)
- post AGB catalog

**Notes:**
In the course of the Dyson Sphere search I have accumulated about a thousand fits to LRS spectra. I have wondered if there is something more conventional that could be done with this data. Good spectroscopy on C star spectroscopic lines can tell quite a bit about the surrounding dust cloud. Unfortunately the IRAS spectroscopy data is not all that strong. Variability in carbon stars is another interesting area. The IRAS data represents an interesting lever arm back in time for looking at this. On the other hand this is probably a domain for dedicated experts. Finally I have uncovered a number of what appears to be misclassified sources. Can I find some way to rectify these classifications? 

## Summary

- Artifacts like pyramids, Dyson Spheres, and Kardashev civilizations are “natural” and don’t require purposeful ETI signals

- IRAS – good Dyson Sphere search instrument
- Searches are confounded by many other signatures
- Few sources at most with
-            IRAS Low Resolution Spectrometer

- Cosmic archaeology
-      SETI cultural signals
-      Type III Kardashev ala Annis
-      Cultural planetary atmosphere signals
-      Astroengineering – Dyson Spheres
-      Stellar engineering – Martin Beech

**Notes:**
In summary, artifacts like Dyson Spheres offer a different paradigm for searching for extraterrestrial intelligence. Like pyramids and other artifacts from archaeology, Dyson Spheres require no purposeful effort to originate a signal. The IRAS infrared satellite has been a useful tool for whole sky Dyson Sphere searches. Even with the problem of angular resolution it has offered the best whole sky tool. This search indicates that there are only a few at best pure Dyson Spheres candidates in a sample of a million suns. One does find good Planck fits but most of these are surrogates like some carbon stars.  
New opportunities to look for life signatures and cosmic archaeology are at hand. The Allen Telescope is a new tool to look for cultural radio signatures. Extrasolar planetary atmosphere investigations have begun and within a decade or so may be able to see cultural atmospheric signatures. Hopefully there are other hypothetical cosmic archaeology signatures that can be checked. For example, what would you do if your sun turned into a Red Giant and was about to envelope your planetary home and burn you to a crisp? Do astrophysicists uniformly believe that there would be no way out?  Thanks for your interest.