Contains research objectives and reports on three research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)U. S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-0009National Science Foundation (Grant GP-7046)National Aeronautics and Space Administration (Contract NSR-22-009-120)National Aeronautics and Space Administration (Grant NsG-419

Barrett, Alan H.

Burke, Bernard F.

Moran, J. M., Jr.

Papadopoulos, George D.

Reifenstein, E. C., III

Wilson, T. C.

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VII. RADIO ASTRONOMYAcademic and Research StaffProf. A. H. Barrett Prof. W. B. Lenoir Dr. S. H. ZiskProf. B. F. Burke Prof. R. M. Price J. W. BarrettProf. D. H. StaelinGraduate StudentsR. M. Blotky Sara E. Law E. C. Reifenstein IIIM. S. Ewing J. M. Moran, Jr. L. W. Schaper, Jr.N. E. Gaut P. C. Myers P. R. SchwartzW. W. Gebhart G. D. Papadopoulos J. W. WatersL. P. A. Henckels P. W. Rosenkranz T. L. WilsonH. F. Hinteregger W. J. WilsonRESEARCH OBJECTIVES AND SUMMARY OF RESEARCH1. Development of long-baseline interferometry techniques and studies of smallangular diameter sources. The use of highly stable atomic frequency standards for fre-quency and time control has made possible the construction of radio interferometers ofarbitrarily long baseline. Separate stations have been operated simultaneously at theHaystack facility of Lincoln Laboratory, M. I. T., the National Radio Astronomy Obser-vatory at Green Bank, West Virginia, and the Hat Creek Observatory of the Universityof California at Berkeley, giving spacings of up to 19, 500, 000 wavelengths at OH fre-quencies and resolution of . 005 second of arc. Studies of the OH regions have demon-strated structure of the order of . 01 second of arc, and an unresolved component of thequasar 3C273B has been shown to be smaller than . 005 second of arc. The observationscontinue and the technique shows promise of yielding interesting information concerningthe validity of general relativity and can also be used as a potentially powerful geophys-ical technique.2. Measurements of the cosmological microwave black-body radiation. A mea-surement of the isotropic radio background was made at 9. 24-mm wavelength, whichyielded a background temperature of 3. 16 ±. 26°K. Plans are being made to extend thetechnique to much shorter wavelengths in the vicinity of 1 mm, beyond the Planck min-imum, thereby giving a sensitive test to the cosmological interpretation.3. Galactic studies. Making use of measurements of the hydrogen recombinationline 109a, we have completed a survey of H II regions in the galaxy. The observationswere made at 6 cm, using the 140 ft telescope of the National Radio Astronomy Obser-vatory, and interpretation of the results is proceeding. One of the members of ourgroup will travel to Australia, to extend the survey to the Southern sky, using the 210 fttelescope of the CSIRO Radio Physics Laboratory.4. Aperture synthesis. A 2-cm interferometer is nearing completion, and willbe used to make high-resolution studies of the bright radio sources. The interfer-ometer will make use of an on-line computer for real-time data reduction, and isintended to serve as a prototype for further high-resolution instruments for continuumstudies.*This work was supported principally by the National Aeronautics and Space Admin-istration (Grant NsG-419 and Contract NSR-22-009-120); and in part by the Joint ServicesElectronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force, under Con-tract DA 28-043-AMC-02536(E), the U. S. Navy (Office of Naval Research) under Con-tract N00014-67-A-0204-0009, and the National Science Foundation (Grant GP-7046).QPR No. 88(VII. RADIO ASTRONOMY)5. Study of the microwave continuum from galactic and extragalactic radio sourcesat short centimeter wavelengths. The variable quasi-stellar radio sources are observedat 3. 75 cm and 2. 0 cm wavelengths to determine their time-variant spectra and polari-zation properties.6. Study of microwave emission and absorption by the terrestrial atmosphere, withparticular emphasis on meteorological satellite application. This work has includedground-based observations of atmospheric water vapor and ozone, and balloon observa-tions of microwave emission by molecular oxygen. Up-looking balloon observations havebeen conducted to determine the line absorption coefficient, and down-looking flights havebeen carried out to test inversion techniques to recover the temperature profile.A. H. Barrett, B. F. BurkeA. GALACTIC STUDIES OF THE HYDROGEN RECOMBINATION LINEThe second phase of our 6-cm 109a recombination line survey has been completed,and data analysis is proceeding. In the first phase, with observations made last spring,we have completed analysis of line intensities and radial velocities of 80 galacticsources. A line was detected in 52 of these sources, and a comparison of the observa-tions with neutral hydrogen line (21 cm) surveys has been made. It is clear that mostof the intense H II regions are concentrated in the inner regions of the galaxy, fromroughly 4 kpc to 6 kpc, although a few occur farther out. Our latest observations, alsousing the 140 ft telescope of the National Radio Astronomy Observatory, will extend thelist to twice the number of sources, and include nearly every thermal source visible atGreen Bank of flux greater than 6 X 10 mks at 5009 MHz. A detailed analysis is inprogress, and should soon be ready.Observations were also made of the galactic center region, which have shown thatseveral components may be nonthermal, even though their continuum spectrum appearsto be thermal. Three components, with G-numbers (0.5, -0.0) (0.7, -0.0), and (1.1, 0.4)are clearly thermal, and their observed radial velocities indicate that they are not chanceforeground objects, but must participate in the peculiar motions of the central region.B. F. Burke, E. C. Reifenstein, T. C. WilsonB. Ku-BAND INTERFEROMETERThe 17 GHz interferometric system is, at present, in its final stage of construction.Two of the three 8-ft dishes have been mounted on the polar mounts built by the ResearchLaboratory of Electronics shop. A preliminary feed will be completed within a few days,and will be used to measure the efficiency of the antennas.A small computer (PDP-8) was purchased last June for real-time data processingand sytem control. The program has been written and the interface is now under test.The front end and the phase-lock parts of the system are now under test.George Papadopoulos, B. F. BurkeQPR No. 88(VII. RADIO ASTRONOMY)C. STRUCTURE OF W3We have been investigating the structure of the 18-cm OH emission in the H II regionW3. Owing to the small angular size of the emitting region, it has been necessary touse very long-baseline radio interferometers to resolve the source. The Agassiz-Millstone interferometer,l with baseline of 74, 000 X, revealed that the spectral featuresin the 1665-MHz spectra were spatially separated by roughly 1 arc second. In June 1967,the Haystack antenna and the 140 ft antenna at the National Radio Astronomy Observatorywere linked to give a baseline length of 4. 6 X 106 . This instrument showed that someof the individual spectral features were . 02 second of arc in size or smaller. 2In July 1967, an interferometer experiment was carried out between Hat Creek, Cal-ifornia, and NRAO to give a baseline of 19. 5 X 106 X and a fringe spacing of . 01 secondof arc. The signals received at each site were clipped and sampled and recorded onmagnetic tape. Later the tapes were brought together and the data were crosscorrelated.Atomic frequency standards were used to control the local oscillators and samplers.o 0.84a-U)u_0z01.2zJw-45.1 (R)43.7 (R)-41.7 (R)I NRAO - HAYSTACKNRAO- BERKELEY-46.4 (L)MAP OF W3OH REGION1000 A.U.AT 1700 PC1.4 K-45.5 (L)I IO. 10 0.05RIGHT ASCENSION OFFSET (sec)I0.00Fig. VII-1. Map of OH sources near W3.QPR No. 88(VII. RADIO ASTRONOMY)Because the spectral features originate from slightly different locations the inter-ference fringes that they produce move at slightly different frequencies. By measuringthe relative fringe frequency caused by two spectral features at many orientations ofthe baseline, the separation of these features can be computed. Because this is a rela-tive measurement the instrumental effects of uncertainty in the baseline orientation andthe frequency of the atomic standards are removed. For an integration time of 2 min-utes the relative fringe frequency can be measured to . 0001 Hz out of a total fringe fre-quency of approximately 1000 Hz. Hence several measurements are enough to computethe relative positions to . 1 second of arc. Figure VII-1 shows a detailed map of the OHsource near W3 comprising 2 square arc seconds, or approximately one hundredbillionth of the entire sky.We were not able to resolve the -43.7 km/sec component, which gives an upper limiton its size of .005 second of arc. Its linear dimension is less than 8 A. U., and itsbrightness temperature is greater than 4 X 10 12K. The features at -45. 1 GHz and-41. 7 GHz are double, with separations ~. 02 second of arc, while the feature at-46. 4 GHz is elongated or possibly double with dimensions . 01 X . 005 second of arc.J. M. Moran, B. F. Burke, A. H. BarrettReferences1. J. M. Moran, A. H. Barrett, A. E. E. Rogers, B. F. Burke, B. Zuckerman,H. Penfield, and M. L. Meeks, Astrophys. J. 148, 2 (1967).2. J. M. Moran, B. F. Burke, and A. H. Barrett, Quarterly Progress Report No. 87,Research Laboratory of Electronics, M. I. T., October 15, 1967, pp. 11-15.QPR No. 88

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