Interstellar Communication Channel Search of 49 Target Stars
Closer than 11.5 pc
M G Zadnik1, J Winterflood2, A J Williams2, K J Wellington3, R Vaile4, J Tarter5, R P Norris3, G Heiligman6, D G Blair2 and P Backus5
1 Dept of Applied Physics, Curtin University of Technology, W Australia
2 Dept of Physics, University of Western Australia, W Australia
3 CSIRO ATNF, PO Box 76, Epping, NSW 2121, Australia
4 Dept of Physics, University of Western Sydney, NSW, Australia
5 SETI Institute, Mountain View, California, USA
6 Sterling Software, SETI Institute, Mountain View, California, USA
Contact Person: M G Zadnik (m.zadnik@curtin.edu.au)
Abstract
We report on a search for narrow band emissions from the vicinity of 36 solar type (F6 to K4) target stars and 13 other non-solar type stars within 11.5 parsecs at 5 possible interstellar beacon frequencies of p*fH, 2p*fH, e*fOH , e*(fOH +fH) and 3He (4.462, 8.925 4.532, 8.393 and 8.666 GHz respectively). The frequencies were selected by scaling important naturally occurring lines by fundamental constants. The stars were selected for a distance of less than 11.5 parsecs to give sufficient time for a nearby civilisation to have detected early Earth radio leakage signals and to have replied. The search was carried using the 64m Parkes telescope with the Phoenix instrumentation and 22m Mopra telescope for candidate verification. The instrument combination allowed for a low interference, high resolution, high sensitivity search. We did not detect any signals from any of the target stars. If a civilisation at a distance of 10 pc had beamed 20 kW signals at us using a 100-m dish, we would have detected the transmission at the 10 sigma level. Thus we can exclude signals above this level.
Introduction
This paper describes the third in a series of searches for narrow band interstellar communication channels (magic frequencies) using the Parkes 64 m Radio Telescope in Australia. We have argued previously that these narrow band communication channels will be related to wavelengths of fundamental physical importance, such as the hydrogen line at 21 cm and the hydroxyl line at 18 cm scaled by fundamental mathematical constants such as p and e (Blair, 1986; Blair et al, 1992; Blair and Zadnik, 1993 which lists 55 such frequencies). Communities wanting to communicate will choose frequencies which should be readily determinable by humans. These frequencies are unlikely to be confused with natural sources and are within the 1-20 GHz window of frequencies for which interstellar communication is likely. The window is limited by Galactic synchrotron radiation on the low end and by quantum limits on the high end (one photon per bit of information implies higher energy cost). In addition, water absorption in the Earths atmosphere reduces our sensitivity above 10 GHz.. We did not include frequencies in the 1 to 3 GHz range as these had been covered by the Phoenix project (Backus et al, 1996).
Previous observations took place in May 1990 and May 1991 at Parkes and searched solar type stars at the frequency of 4.462336275 GHz ( p x the 1420 MHz hydrogen line) (Blair et al, 1991; Blair et al, 1992). The first series of observations, in 1990 involved monitoring about 100 nearby stars (< 110 pc) for the presence of this narrow spectral line.
In the second series, in 1991, the previously observed stars were re-examined and another 60 new stars, together with seven globular clusters, were observed, again using the hypothesised interstellar communications channel frequency of 4.462336275 GHz. The frequency was Doppler corrected for the solar barycentre, target barycentre and Cosmic Microwave Background (CMB) reference frames. Null results, down to a three sigma flux limit of 2 Jy (6 Jy in CMB frame), were used to set an upper limit of 108 years on the lifetimes during which extraterrestrial civilisations used the hypothesised beacon technique to make contact with emerging civilisations (Blair et al, 1992).
New Observations
The third series of observations described in this paper differs primarily from the previous two in the following ways.
1 We used the Phoenix back-end instrumentation (see Backus et al. 1996 and Dreher et al. 1996 for detailed descriptions of the Phoenix systems) together with the ATNF 4 and 8-GHz receivers; (a) the bandwidth was increased (from 50 and 500 kHz in previous observations), to 20 MHz which is wide enough to encompass Doppler shifts due to relative motions of the sources and the Earth, (b) the resolution was increased (from 100 and 1000 Hz) to 1 Hz., and (c) the use of the 22 m Mopra telescope running in parallel with Parkes with the automated Phoenix procedure allowed for candidate verification.
2 We have increased the number of magic frequencies for observation to 5- p*fH, 2p*fH, e*fOH , e*(fOH +fH) and 3He (4.462336273, 8.924672545, 4.532350, 8.393412 and 8.665650 GHz).
3 We observed target stars within 11.5 parsec (see Table 1). This distance was chosen as it is now over 70 years that the Earth has been leaking narrow band radio waves (since about 1923) which would show up as departures from the blackbody spectrum of the Sun to extraterrestrial communities. Should communities choose to communicate with us, sufficient time has now elapsed for us to receive return signals from those within 36 light years.
The search was carried out over 48 hours from 25 and 27 June, 1995. The Parkes-Phoenix instrument combination allowed for a low interference, high resolution, high sensitivity search. Of the 49 stars observed, 43 were observed with the 4 GHz frequencies, 40 with the 8 GHz frequencies and 34 with all five frequencies. 77% of the observations were for 96 frames (138 seconds). The system temperature at 8 GHz frequencies was between 52.2 and 58.2 K, corresponding to a flux sensitivity of 3.5 Jansky for 192 frames (276 seconds).
Results
Very low levels of interference were experienced at all search frequencies. A number of follow up observations were required and almost all that were required were for low significance detections near to the noise threshold. None required follow up tests by operators. A carrier and two sidebands from the space craft Voyager 2 (distance of ~ 44 AU transmitting at ~20 W) were easily detected at frequencies 8420.172, 8420.195 and 8420.217 MHz.
Conclusions
We did not detect any signals from any of the target stars. If a civilisation at a distance of 10 pc had beamed 20 kW signals at us using a 100-m dish, we would have detected the transmission at the 10 sigma level. Thus we can exclude signals at or above this level.
Acknowledgements
We thank Dr Ross Kirkman for assistance during the observations, and we thank the ATNF staff for setting up the equipment for this experiment.
References
Backus et al, 1996, paper presented at the International Astronautical Federation, 46th Congress, Oslo, Norway, 1995. To be published in a special edition of Acta Astronautica, J. Heidmann (ed).
Dreher et al., 1996, paper presented at the International Astronautical Federation, 46th Congress, Oslo, Norway, 1995. To be published in a special edition of Acta Astronautica, J. Heidmann (ed).
Blair, D.G.: 1986, Nature, 319, 270
Blair D. G., Norris R., Troup E., et al., 1991, Bioastronomy, The Search for Extraterrestrial Life, Heidmann, J and Klein M. J.,
(eds) Lecture Notes in Physics 390. Springer-Verlag, Berlin.
Blair D. G., Norris, R.P., Troup E., Twardy R, Wellington K.J., Williams A. J., Wright A. and Zadnik M.G., 1992, MNRAS 257,105-109.
Blair D. G. and Zadnik, M. G., 1993, Research Note, Astron. Astrophys, 278, 669-672.
Hoffleit, D.: The Bright Star Catalogue, Yale University Observatory.
Latham D., Soderblom D., and Henry T., 1994, private communication.
TABLE 1
Target list of 49 main-sequence stars, south of +20 degrees Dec, and closer than 11.5 pc from Hoffleit (1982) and The SETI Institutes Best and Brightest target list from Latham, Soderblom, and Henry (1994).
Hofflei HD Observing RA RA RA DEC DECMi DEC SPEC TYPE Distance t List number Freq* Hrs Mins Secs Deg ns Secs Parsec 225213 C and X 00 05 24 -37 21 26 M4V 4.5 77 1581 C and X 00 20 04 -64 52 29 F9V 7.2 2151 C and X 00 25 45 -77 15 15 G2IV 6.4 222 C and X 00 48 23 05 16 50 K2V 6.9 486 10361 C and X 01 39 48 -56 11 42 K2V+K3 6.7 493 X 01 42 30 20 16 07 K1V 8.4 509 C and X 01 44 04 -15 56 15 G8V 3.6 637 C and X 02 10 26 -50 49 28 K1V 11.1 857 X 02 52 32 -12 46 10 K2V 8.3 20766 C and X 03 17 46 -62 34 31 G2V 10.7 1010 20807 C and X 03 18 13 -62 30 22 G1V 11.4 996 X 03 19 22 03 22 13 G5V 9.3 1008 20794 C and X 03 19 56 -43 04 11 G5V 6.3 1084 X 03 32 56 -09 27 30 K2V 3.3 1325 26965 X 04 15 16 -07 39 12 K1Ve+D 4.8 1543 X 04 49 50 06 57 41 F6V 8.0 33793 C and X 05 11 41 -45 01 08 M0V 3.9 1983 C and X 05 44 28 -22 26 54 F6V 7.8 2261 43834 C and X 06 10 14 -74 45 11 G5V 8.8 C and X 06 45 09 -16 42 58 A1Vm 2.6 C and X 07 53 15 -67 47 31 DQ9 6.9 C and X 08 43 18 -38 53 00 K1V 10.4 C and X 10 16 46 -11 57 41 (K) 9.3 C and X 10 44 32 -61 11 38 m 4.5 4458 C and X 11 34 29 -32 49 53 K0V 9.4 C 11 45 43 -64 50 31 DQ6 4.6 4523 102365 C and X 11 46 31 -40 30 02 G5V+? 10.3 4540 C and X 11 50 42 01 45 53 F9V 9.6 5019 C and X 13 18 24 -18 18 41 G6V 8.7 C 14 29 43 -62 40 47 dM5e 1.3 5459 128620 C and X 14 39 36 -60 50 07 G2V+K0 1.3 5544 C and X 14 51 23 19 06 04 G8Ve+K4V 6.4 5568 C and X 14 57 28 -21 24 56 K4V 5.8 C 15 32 13 -41 16 31 M3 6.1 6098 147584 C and X 16 28 28 -70 05 04 G0V 10.8 6171 C and X 16 36 21 -02 19 29 K2V 10.8 6402 C and X 17 15 21 -26 36 05 K0V 5.3 6426 C and X 17 18 57 -34 59 23 K3V+K5V 7.1 6416 C and X 17 19 03 -46 38 02 G8-K0V 7.6 C 19 20 48 -45 33 27 M4.5 5.7 190248 C and X 20 08 44 -66 10 55 G8V 5.7 7703 191408 C and X 20 11 12 -36 06 05 K3V+M3 5.6 191849 C 20 13 53 -45 09 51 M0V 6.1 7722 C 20 15 17 -27 01 58 K0V 8.1 202560 C 21 17 15 -38 52 03 M0Ve 3.9 8181 C and X 21 26 27 -65 21 58 F6V 9.0 204961 C 21 33 34 -49 00 33 M1V 4.7 8387 209100 C and X 22 03 22 -56 47 10 K5Ve 3.5 217987 C 23 05 52 -35 51 12 M2Ve 3.5
* C indicates observations at 4.462 and 4.532 GHz, X at 8.393, 8.666 and 8.925 GHz, and C and X indicates observations were made with all 5 frequencies.