Sweep-frequency measurements of solar bursts.
Sweep-frequency measurements of solar nonthermal radio emissions in meter and decimeter wave ranges, discussing low RF spectrograph and interferometer observations
SWEEP FREQUENCY↗
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Radio Astrometry
The utilization of conventional and VLBI interferometer techniques for accurate determination of UTI, polar motion, and radio source position catalog data is discussed.
Johnston, K. J.↗
Feeding IC 342: The nuclear spiral of a starburst galaxy
IC 342 is a large nearby (1.8 Mpc, Turner and Hurt, 1991, hereafter T&H) spiral galaxy undergoing a moderate nuclear starburst. T&H have previously mapped the inner arcminute in CO-13(1-0) using the Owens Valley Millimeter Interferometer and found evidence that the nuclear molecular gas takes the form of spiral arms in a density wave pattern. They suggest that radial streaming along the arms may channel gas from the exterior of the galaxy into the nucleus, feeding the starburst. We have mapped the CO-12(1-0) emission of the inner 2 kpc of IC 342 at 2.8 inch resolution using the Owens Valley Radio Observatory (OVRO) Millimeter Interferometer. The greater sensitivity of CO-12 observations has allowed us to trace the spiral pattern out to a total extent of greater than 1 kpc. The CO-12 observations extend considerably the structure observed at CO-13 and offer further evidence that a spiral density wave may extend from the disk into the nucleus of IC 342.
Levine, D.↗
The Square Kilometre Array
The Square Kilometre Array (SKA) will be the premier instrument to study radiation at centimetre and metre wavelengths from the cosmos, and in particular neutral hydrogen, the most abundant element in the universe. The SKA will probe the dawn of galaxy formation as well as allow advances in many other areas of astronomy, such as fundamental physics, astro-biology and cosmology. The SKA will have a collecting area of up to one million square metres spread over at least 3000 km, providing a collecting area more than twenty times greater than the current largest radio telescope. Its field of view on the sky will be several tens of square degrees with potentially several large (100 square degrees) independent beams at the lower frequencies, providing a survey speed many thousands of times greater than current facilities. This paper summarises the key science drivers of the SKA and provides an update on the international project.
interferometers↗
Deployment of a tethered orbiting interferometer
Tethered orbiting interferometer configurations for future Radio Astronomy Explorer satellites, discussing gravitational stabilization and delta launching into orbit as single payload
Swet, C. J.↗
Solar microwave bursts - A review
Observational and theoretical results on the physics of microwave bursts that occur in the solar atmosphere are reviewed. Special attention is given to the advances made in burst physics over the last few years with the great improvement in spatial and time resolution, especially with instruments like the NRAO three-element interferometer, the Westerbork Synthesis Radio Telescope, and more recently the Very Large Array. Observations made on the preflare build-up of an active region at centimeter wavelengths are reviewed. Three distinct phases in the evolution of cm bursts, namely the impulsive phase, the post-burst phase, and the gradual rise and fall, are discussed. Attention is also given to the flux density spectra of centimeter bursts. Descriptions are given of observations of fine structures with temporal resolution of 10-100 ms in the intensity profiles of cm-wavelength bursts. High spatial resolution observations are analyzed, with special reference to the one- and two-dimensional maps of cm burst sources.
Kundu, M. R.↗
Aperture synthesis CO observations of the inner disk of NGC 1068
NGC 1068 is probably the nearest galaxy with both a high rate of star formation and a high luminosity active nucleus. About one-half of the total IR luminosity originates in a disk approximately 30 seconds in size, which has been taken as evidence for a high rate of massive star formation (Telesco et al. 1984). Previous CO line observations have shown the existence of a ring at the outer boundary of the inner disk (Myers and Scoville 1987). Although these observations have proved that this ring is extremely rich in molecular gas (as suggested by Scoville et al. 1983), the angular resolution (approx. 6 seconds) was not high enough to resolve its structure. New aperture synthesis observations of the CO (J=1 to 0) emission in the inner disk of NGC 1068 have been carried out with the Owens Valley Radio Observatory (OVRO) mm Interferometer. The new receivers installed for the 88/89 season have allowed researchers to obtain a high sensitivity map of the CO emission. The molecular cloud ring has been resolved and continuum as well as line emission from the nucleus of the galaxy have been detected.
Planesas, P.↗
Observations of the CO bulge on Venus and implications for mesospheric winds
Observations of CO at 2.6 mm (115.27 GHz) were made with the Owens Valley Radio Observatory (OVRO) millimeter interferometer in 1986 and 1988, yielding high-quality disk-resolved spectra which were inverted to determine the CO mixing ratio profile from distinct regions on the disk, allowing us to map the distribution of CO in the upper mesosphere of Venus both horizontally and vertically. The 1986 observations were of the morning terminator and were particularly useful in searching for a suspected CO maximum ('bulge') on the nightside. The resulting CO mixing ratio profiles were mapped for various altitudes as functions of latitude and local time, and we report that we have resolved the previously inferred CO bulge. The bulge increases in magnitude from a small day-night variation at 90 km to an extensive nightside peak at 100 km, the upper limit of our observations. The peak bulge-to-dayside ratio approached 20-30 at 100 km in 1986 and may have been as large as 50-100, assuming late-afternoon CO abundances found in 1988 were similar to those in 1986. Three-dimensional mapping shows that in the upper mesosphere the bulge was displaced from local midnight toward the morning equator, centered at 3:30 AM local time. Using the qualitative model of mesospheric circulation on Venus proposed by Clancy and Muhleman (1985, 1991), we explain this shift in terms of strong retrograde zonal winds throughout the mesosphere, matching the directly detected mesospheric circulation (Shah, K., D. O. Muhleman, and G. L. Berge 1991) observed with the same dataset in 1988.
Gurwell, Mark A.↗
Radio astronomy
Use of the Tidbinbilla Interferometer to refine the source positions in the Parkes 2.7 GHz survey of the southern sky is described. A result of the first phase of this work was the identification of a quasi-stellar object which appears to be the most remote object yet observed. This object has a red shift of 3.78 (PKS 2000-330, and a velocity of recession equal to 91% of that light. Based on Hubble's law, PKS 2000-330 appears to be 12 billion light years away.
Shaffer, R. D.↗
A Multiwavelength Study of Cygnus X-3
We present a global comparison of long term observations of the hard X-ray (20-100 keV), soft X-ray (1.5-12 keV), infrared (1-2 micron) and radio (2.25, 8.3 and 15 GHz) bands for the unusual X-ray binary Cygnus X-3. Data were obtained in the hard X-ray band from CGRO/BATSE, in the soft X-ray band from Rossi Xray Timing Explorer (RXTE)/ASM, in the radio band from the Green Bank Interferometer and Ryle Telescope and in the infrared band from various ground based observatories. Radio flares, quenched radio states and quiescent radio emission can all be associated with changes in the hard and soft X-ray intensity. The injection of plasma into the radio jet is directly related to changes in the hard and soft X-ray emission. The infrared observations are examined in the context of these findings.
McCollough, M. L↗
CO aperture synthesis of NGC 4038/9 (ARP 244)
Researchers present high-resolution (approx. 6 seconds) CO observations of the merging galaxies NGC 4038/9 made with the Owens Valley Radio Observatory (OVRO) Millimeter Wave Interferometer. The CO observations of Arp 244 were obtained between April and June 1988 using the OVRO Millimeter Wave Interferometer. Two fields with phase centers near the NGC 4039 nucleus and near the NGC 4038 nucleus were observed. The size of the synthesized beam is approximately 6.5 x 7 seconds at PA=72 degrees. The rms in a single cleaned channel map is 0.06 Jy beam(exp -1), corresponding to a brightness temperature of 0.12 K over the synthesized beam. Contour maps of the integrated CO intensity for both interferometer fields are shown. Three CO concentrations are evident. Two are centered near the nuclei of NGC 4038 and NGC 4039, closely correlated with H alpha and radio continuum maxima. A third CO emission region lies about 25 seconds northeast of the NGC 4039 nucleus. A number of radio continuum, H alpha, and 10 micron emission knots appear in this region. The total integrated intensity at the northern nuclear source, 302 K km/s, leads to a molecular mass of 8.3 by 10 to the 8th power solar mass assuming a Galactic CO to H2 conversion factor of 3.0 x 10 to the 20th power H2 cm(-2) (K km/s)(-1). The integrated CO intensity of the southern nuclear source leads to a molecular mass of 2.4 x 10 to the 8th solar mass. The extranuclear CO concentration contains 1.2 x 10 to the 9th power solar mass of molecular gas, extending over 170 km/s, and is resolved in a number of channels. Its large size, mass, and morphology strongly suggest that it is an agglomeration of several clumps.
Stanford, S. A.↗
A high declination search at 8 GHz for compact radio sources
With the Haystack-NRAO interferometer (baseline length of 20 million wavelengths at 3.8 cm) 37 sources were observed whose declinations were above 50 deg. Seven of these sources have compact cores with diameters smaller than 5 milliarcsec and with correlated flux densities greater than about 0.5 Jy; the remaining sources have no cores with flux densities above about 0.3 Jy, the sensitivity limit of the interferometer. Two of the sources with detected compact cores, 4C 67.05 and 3C 418, were also observed with longer-baseline interferometers; the diameter of the core of 4C 67.05 was estimated to be smaller than 1 milliarcsec and that of 3C 418 to be smaller than 0.4 milliarcsec. All diameter estimates were based on an assumed circular Gaussian distribution of radio brightness and refer to the contour with brightness density e to the -1/2 power times that of the center. Positions for the detected sources were also obtained from the interferometric data, the uncertainty in these coordinate estimates ranging from 0.04 to 0.6 arcsec. The compact core detected in 3C 390.3 was found to lie near the center of this extended (approximately 4 arcmin in diameter) double radio source and to be coincident to within 1 arcsec with an N galaxy previously identified with 3C 390.3.
Wittels, J. J.↗
2.3-GHz accurate positions and optical identifications for selected Parkes radio sources
Accurate radio positions of 74 extragalactic radio sources contained in the Parkes 2.7-GHz survey were measured at 2.3 GHz with the Tidbinbilla interferometer, located near Canberra, Australia. The radio sources, most of which lie between declinations -30 deg and -35 deg, were measured to an rms positional accuracy of about 3 arcsec relative to a grid of previously identified radio sources. Optical identifications have been made on the basis of positional coincidence alone, without regard to color or morphology, using the UK Schmidt telescope deep IIIa-J sky survey plates. Identifications are suggested and accurate optical positions have been measured for 62 objects brighter than magnitude 22.5 on the IIIa-J plates.
Jauncey, D. L.↗
Radio astronomy
Radio astronomy - Haystack-Millstone OH INTERFEROMETER, K-band spectrum measurements of sun, inference of atmospheric attenuation from balloon flights, and microwave emission
RADIO ASTRONOMY↗
The Tidbinbilla interferometer
This paper describes a technique to detect and identify weak, small-diameter radio sources with flux densities in the millijansky range. An interferometer system is proposed which will use existing 64 m and 24 m antennas of the Tidbinbilla Deep Space Network near Canberra. Design parameters of the system are described, and a schematic is presented with attention to low-noise traveling wave masers, and phase oscillation devices.
Batty, M. J.↗
Geodesy by radio interferometry - Intercontinental distance determinations with subdecimeter precision
Analysis of very-long-baseline interferometer (VLBI) observations yielded estimates of the distances between three radio telescopes in the United States and one in Sweden, with formal standard errors of a few centimeters: Westford, Massachusetts-Onsala, Sweden: 5,599,714.66 + or - 0.03 m; Green Bank, West Virginia-Onsala, Sweden: 6,319,317.75 + or - 0.03 m; and Owens Valley, California-Onsala, Sweden: 7,914,131.19 + or - 0.04 m, where the earth-fixed reference points are defined in each case with respect to the axes of the telescopes. The actual standard errors are difficult to estimate reliably but are probably not greater than twice the formal errors.
Herring, T. A.↗
Quarterly report of the Haystack Observatory
Radio astronomy studies including sensitive interferometers, digital correlators, and related measuring instruments also radar techniques for lunar topography
Source record↗
Large Antenna Control Methods: Current Status and Future Trends
Current methods for control of large antennas, as well as future trends required for improved performance are addressed. Some of the target missions in which these methods would be used are: the Land Mobile Satellite System (LMSS) for communications; the Satellite Surveillance (SSS) for aircraft traffic control; the orbiting Very Long Baseline Interferometer (VLBI), or QUASAT, for radio astronomy; and the Large Deployable Reflector (LDR) for IR and submillimeter astronomy.
Rodriguez, G.↗