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NASA NTRS1979

Radio emission from nova shells

This paper presents data from multifrequency radio observations of the novae HR Del 1967 and FH Ser 1970 made from June 1970 to December 1978 and of V1500 Cyg 1975 made from September 1975 to December 1978. The data for FH Ser and V1500 Cyg constitute a complete history of the important phases of their radio 'light' curves, while all but the rising portion of the optically thick phase of an expanding nova shell is present for HR Del. A simple solution of the spherically symmetric equations of mass and momentum conservation for an isothermal gas, for which pressure gradients are effectively decoupled from the dynamics, is shown to fit the radio data for all three novae quite well. The main features of this model are strong density and velocity gradients that lead to long periods when the 'observable' shell evolves from an optically thick 'disk' to a completely optically thin shell.

Hjellming, R. M.↗

NASA NTRS1979

A model of the Venus atmosphere from radio, radar, and occultation observations

A model is presented of the atmosphere and surface of Venus which best fits in the least-squares sense the available radio-brightness, radar cross-section, radio interferometric, and Mariner 5 and 10 radio occultation observations. The determinations of the radius of the planet obtained by others from radar time-delay measurements are included in the data set. The values of the adjusted parameters are: molar fraction of CO2 = 95 plus or minus 3%; fraction of combined nitrogen and argon = 5 plus or minus 3%; total atmospheric opacity at a wavelength of 1 cm = 19.4 plus or minus 1.3; mean radius of the surface = 6050.7 plus or minus 0.8 km; mean dielectric constant of the surface = 4.1 plus or minus 0.2, and percentage of total opacity due to chemical species other than CO2 = 45 plus or minus 12. The model temperature and pressure at the mean surface are 755 K and 91.4 atm, respectively.

Muhleman, D. O.↗

NASA NTRS1980

150 GHz observations of three radio galaxies

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C 111 were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components are similar, although the compact component in 3C 111 is more luminous at both radio and X-ray wavelengths than the one in Cyg A. The 3C 111 central source was much weaker than anticipated on the basis of prior observations at 90 GHz, perhaps due to variability. Even at 150 GHz, there is no evidence of a high-frequency cutoff in the spectrum of the central source in Cyg A, and variability of this source also is expected. The flux densities of the Cyg A lobes are consistent with the power laws derived at lower frequencies, indicating that no steepening occurs in their spectra out to at least 150 GHz. There is no evidence for a compact, optically thick component in 3C 236.

Kafatos, M.↗

NASA NTRS1979

Accurate radio positions with the Tidbinbilla interferometer

The Tidbinbilla interferometer (Batty et al., 1977) is designed specifically to provide accurate radio position measurements of compact radio sources in the Southern Hemisphere with high sensitivity. The interferometer uses the 26-m and 64-m antennas of the Deep Space Network at Tidbinbilla, near Canberra. The two antennas are separated by 200 m on a north-south baseline. By utilizing the existing antennas and the low-noise traveling-wave masers at 2.29 GHz, it has been possible to produce a high-sensitivity instrument with a minimum of capital expenditure. The north-south baseline ensures that a good range of UV coverage is obtained, so that sources lying in the declination range between about -80 and +30 deg may be observed with nearly orthogonal projected baselines of no less than about 1000 lambda. The instrument also provides high-accuracy flux density measurements for compact radio sources.

Batty, M. J.↗

NASA NTRS1980

Radio scintillations during occultations by turbulent planetary atmospheres

The radio occultation experiment which uses the radio link between the earth and spacecraft passing behind planets has proven to be an important method for remote sensing turbulence in planetary atmospheres. The effects of defocusing and anisotropic irregularities on the turbulence-induced fluctuations of the radio occultation signal are examined. Rytov's method along with geometrical optics is employed to study the frequency spectra and coherences of the log amplitude and phase fluctuations of spherical waves operating at one as well as two frequencies. Comparison with the Mariner 5 2.3-GHz measurements shows good agreement with the theoretical results.

Woo, R.↗

NASA NTRS1980

Plasma oscillations and the emissivity of type III radio bursts

Plasma wave electric field measurements with the solar orbiting Helios spacecraft have shown that intense electron plasma oscillations occur in association with type III solar radio bursts, thereby confirming a well known mechanism for generating solar radio emissions first proposed by Ginzburg and Zhelezniakov in 1958. In this paper the principal characteristics of these plasma oscillations are reviewed and the observed plasma oscillation intensities are compared with recent measurements of the emissivity of type III radio bursts. The observed emissivities are shown to be in good agreement with two current models for the conversion of electrostatic plasma oscillations to electromagnetic radiation.

Gurnett, D. A.↗

NASA NTRS1981

The DSN radio science system

The Radio Science experiments at Voyager 1 Saturn encounter which included two atmospheric occultations, a planetary ring occultation, and ring scattering experiment were supported by Deep Space Stations in Australia (DSS 43) and Spain (DSS 63). The DSN Radio Science System data flow from receipt of the radio signals at the antenna to delivery of the recorded data to the project are described.

Buckles, B. J.↗

NASA NTRS1980

Io control of Jovian radio emission

The possibility of Io controlling Jovian decametric radio emission, particularly in the region below 22 MHz, is discussed. Results of a two-year survey at 26.3 at 26.3 MHz are presented which demonstrate the control of Io over a high-intensity storm component of the radio emission and the independence of a weak radio component from the phase of Io, as was observed at lower frequencies. It is thus hypothesized that Io control is a flux-dependent rather than a frequency-dependent phenomenon, and results of analyses at 18 and 10 MHz which support this hypothesis are presented. The apparent correlation between frequency and Io control is thus shown to result from a selection effect due to the increase of non-Io emission with decreasing frequency and relative antenna detection threshold. This result implies a contiguous Io-controlled source region extending out several Jovian radii along the Io flux tube.

Desch, M. D.↗

NASA NTRS1981

Eddy diffusion coefficient for the atmosphere of Venus from radio scintillation measurements

Estimates are obtained of the vertical mass eddy diffusion coefficient of the Venus atmosphere in the region of turbulence near 60 km on the basis of radio scintillations observed during radio occultation by the atmosphere. The structure constant estimated from Pioneer Venus orbit 18 entrance radio occultation measurements is used, under the assumption that the turbulence is generated by wind-shear, to derive a value of 40,000 sq cm/sec for the vertical mass eddy diffusion coefficient, together with an energy dissipation rate of 20 sq cm/sec and a temperature fluctuation dissipation rate of 0.001 K-squared/sec. Results are noted to fall within the range measured for the earth's troposphere, however, indicate that small-scale turbulence is probably the dominant mechanism for vertical transport near the tropopause in the Venus atmosphere.

Woo, R.↗

NASA NTRS1981

Radio and visible light observations of matter ejected from the sun

An initial set of visible light and radio observations of a coronal transient made with the Coronagraph/Polarimeter experiment on SMM and the radioheliograph at Culgoora, Australia is presented. It is noted that an enormous loop-shaped transient observed on April 7, 1980, exhibited bright material having whiplike, nonradial motions, as well as moving and stationary radio sources. The data make it possible to establish that a moving type IV radio source was located on or very close to the fast-moving loop. The thermal, kinetic, and magnetic energies in the transient are estimated and, for the first time, compared with the radiative energy of the associated flare.

Wagner, W. J.↗

NASA NTRS1981

VLA search for radio emission from stars with solar-type structures

Results are presented of a high-sensitivity search for 6-cm radio emission from stars with evidence of active chromospheric or coronal regions. The data indicate that many of these stars have radio luminosities much less than those that have been found for known radio stars.

Bowers, P. F.↗

NASA NTRS1981

The 2f/p/ circumterrestrial radio radiation as seen from ISEE 3

A narrowband highly spin-modulated radio source has been observed with the radio astronomy experiment on ISEE 3 from a position 0.01 AU upstream of the earth. The source is interpreted as radio line emission generated at twice the local plasma frequency in the vicinity of the earth's bow shock by energetic particles. The bandwidth of the 2f(p) emission varies from less than 3 kHz to more than 20 kHz and is probably broadened by solar wind density variations across the source region. The 2f(p) source is visible about 50% of the time, and the true position of its centroid is usually located within 30 earth radii of the subsolar point, but at times is observed at a distance of up to 60 earth radii. But most of these variations might result from changes in the orientation of the polarization vector in a partially polarized source or from refraction across an electron density front.

Hoang, S.↗

NASA NTRS1981

Concurrent radio, infrared, optical and X-ray observations of the nucleus of the Seyfert galaxy NGC 4151

The nucleus of the Seyfert galaxy NGC 4151 was observed during May and June 1977 at X-ray energies from 20 to 200 keV using the high-energy X-ray spectrometer on OSO 8 at radio frequencies of 2695 and 8085. Data were also taken in the visual, and at infrared wavelengths of 1 to 2 microns, and from 2 to 6 keV using the OSO 8 proportional counter. Optical data showed variability by a factor of 2 within the observing period, which is comparable to the variability in the 2 to 6 keV X-ray flux. No variability, however, was measured at infrared or radio frequencies. The composite spectrum from radio to gamma-ray is plotted, and it is found that the optical and X-ray fluxes varied during the observing period, although it is not known if they varied concurrently.

Beall, J. H.↗

NASA NTRS1981

High resolution X-ray and radio images of the Crab-like supernova remnant G21.5-0.9

The Crab-like supernova remnant G21.5-0.9 has been imaged at 6 cm wavelength with the VLA and between 0.1-4 keV with the Einstein Observatory. Both the X-ray and radio images show a centrally peaked distribution of extended emission with no indication of a pointlike component. In contrast, the linearly polarized radio emission is distributed in a ring with a distinct central minimum. The electric vectors of the polarized radio emission are oriented circumferentially. The data support a Crab-like model for G21.5-0.9, but one in which a lower percentage of the radiated flux is emitted as X-rays relative to the Crab Nebula.

Becker, R. H.↗

NASA NTRS1981

Solar radio bursts of spectral type II, coronal shocks, and optical coronal transients

An examination is presented of the association of solar radio bursts of spectral type II and coronal shocks with solar flare ejecta observed in H-alpha, the green coronal line, and white-light coronagraphs. It is suggested that fast-moving optical coronal transients should for the most part be identified with piston-type phenomena well behind the outward-traveling shock waves that generate type II radio bursts. A general model is presented which relates type II radio bursts and coronal shocks to optically observed ejecta and consists of three main velocity regimes: (1) a quasi-hemispherical shock wave moving outward from the flare at speeds of 1000-2000 km/sec and Alfven Mach number of about 1.5; (2) the velocity of the piston driving the shock, on the order of 0.8 that of the shock; and (3) the regime of the slower-moving H-alpha ejecta, with velocities of 300-500 km/sec.

Maxwell, A.↗

NASA NTRS1981

Radio observations of comets

Three general techniques of radio science used to attempt to observe comets are discussed: spectral line, continum and radar observations. Of these, only radio spectral line observations achieved a degree of success but, more often than not, the results was negative. Cometary excitation and reasons why radio searches can fail were examined.

Snyder, L. E.↗

NASA NTRS1982

The DSN radio science system Mark 3, 1980

The DSN Radio Science System supported the Voyager 2 Saturn encounter radio science experiments in August 1981. Support for these experiments was provided by all the Deep Space Stations of the DSN. However, the critical support for the Saturn occultation and ring scattering experiment was provided at DSS 43 by the medium-band open-loop recording system. The DSN Radio Science System is descried and the recent implementation at DSS 43 is emphasized.

Buckles, B. J.↗

NASA NTRS1982

Neutral hydrogen in elliptical galaxies with nuclear radio sources and optical emission lines

An H I detection survey of eleven elliptical galaxies with powerful nuclear radio sources was conducted, using the 305 m antenna of Arecibo Observatory, to test the hypothesis that large H I mass is conductive to the formation of nuclear radio sources in elliptical galaxies. The H I was detected in emission in UGC 09114 and was possibly detected in absorption in UGC 06671. Observations of the remaining galaxies were not sensitive enough to support or refute the hypothesis. Data was combined from other H I surveys and spectroscopic surveys to search for correlations of H I mass with other galactic properties and environmental conditions. Strong correlations of (O II) lambda 3727 emission with H I content and with nuclear radio power were found. The latter two properties may simply indicate, respectively, whether a significant amount of gas is available to be ionized and whether energy is provided by nuclear activity for ionization. No dependence of H I content on optical luminosity or on degree of isolation from other galaxies was found.

Dressel, L. L.↗