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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Solar radio emission at 1.2 mm wavelength.

A 36-ft radio telescope was used in the investigations. The 1.2 mm wavelength receiver connected to the telescope is a helium-cooled germanium bolometer. The 1.2 mm solar maps were obtained by scanning the sun in right ascension at the rate of 1 deg per minute. A temperature of 6000 K was assumed for the 1.2 mm quiet sun temperature for all solar maps. Eight maps at 1.2 mm were obtained on six different days. The 1.2 mm regions are rather large and without much structure; they are closely associated with Ca-plage regions.

Kundu, M. R.↗
NASA NTRS1988

Uranus radio emissions

An overview of the Voyager 2 Planetary Radio Astronomy instrument observations of the planet Uranus is presented. From these observations, a number of inferences have been made including the rotation period of the interior of the planet and the source locations of several of the radio components.

Kaiser, Michael L.↗
NASA NTRS1993

Stochastic Growth Theory of Type 3 Solar Radio Emission

The recently developed stochastic growth theory of type 3 radio sources is extended to predict their electromagnetic volume emissivities and brightness temperatures. Predicted emissivities are consistent with spacecraft observations and independent theoretical constraints.

Robinson, P. A.↗
NASA NTRS1991

Nonthermal radio emission from the X-ray-bright K5 IV star 1E 1751 + 7046

VLA observations are analyzed of the K5 IV star 1E 1751 + 7046, which is known to be an X-ray source on the basis of Einstein observations and which shows some similarity to stars of the FK Comae type. Radio continuum emission has been detected at 3.6, 6, and 20 cm, and the spectral energy distribution is nearly flat. There is no evidence for circular polarization, and upper limits are given. The 6-cm flux is roughly one order of magnitude less than reported in a previous VLA observation, indicating that this star may flare at radio wavelengths. The inferred radio variability and the nearly flat spectral energy distribution suggest that the emission is of nonthermal origin. A variety of possible emission mechanisms is examined, and it is concluded that the emission is best explained in terms of a gyrosynchrotron/synchrotron model with the electrons following a power-law energy distribution. A brief comparison of the radio properties of 1E 1751 + 7046 with FK Comae-like stars and RS CVn systems is given.

Skinner, Stephen L.↗
NASA NTRS1988

The evolution of the radio emission from Kepler's Supernova remnant

High-resolution radio maps of Kepler's Supernova remnant (SNR) using all four arrays of the VLA have been obtained at wavelengths of 20 and 6 cm. They show the complete structure of the remnant; all features are resolved with sizes greater than about 2 arcsec, and the relative brightness of the smooth component near the center is about 1/4 the brightness of the rim. The results have been compared with earlier more limited data to measure changes in the remnant over a four-year time span. The SNR is expanding with a mean rate of R proportional to t exp 0.50 with considerable variations around the shell. Values range from R proportional to t exp 0.35 on the bright northern rim to R proportional to t exp 0.65 on the eastern part of the shell. The measurements are consistent with expansion into a variable circumstellar medium.

Dickel, John R.↗
NASA NTRS1987

X-ray studies of quasars with the Einstein Observatory. IV - X-ray dependence on radio emission

The X-ray properties of a sample of 114 radio-loud quasars observed with the Einstein Observatory are examined, and the results are compared with those obtained from a large sample of radio-quiet quasars. The results of statistical analysis of the dependence of X-ray luminosity on combined functions of optical and radio luminosity show that the dependence on both luminosities is important. However, statistically significant differences are found between subsamples of flat radio spectra quasars and steep radio spectra quasars with regard to dependence of X-ray luminosity on only radio luminosity. The data are consistent with radio-loud quasars having a physical component, not directly related to the optical luminosity, which produces the core radio luminosity plus 'extra' X-ray emission.

Worrall, D. M.↗
NASA NTRS2000

Theory of Type 3 and Type 2 Solar Radio Emissions

The main features of some current theories of type III and type II bursts are outlined. Among the most common solar radio bursts, type III bursts are produced at frequencies of 10 kHz to a few GHz when electron beams are ejected from solar active regions, entering the corona and solar wind at typical speeds of 0.1c. These beams provide energy to generate Langmuir waves via a streaming instability. In the current stochastic-growth theory, Langmuir waves grow in clumps associated with random low-frequency density fluctuations, leading to the observed spiky waves. Nonlinear wave-wave interactions then lead to secondary emission of observable radio waves near the fundamental and harmonic of the plasma frequency. Subsequent scattering processes modify the dynamic radio spectra, while back-reaction of Langmuir waves on the beam causes it to fluctuate about a state of marginal stability. Theories based on these ideas can account for the observed properties of type III bursts, including the in situ waves and the dynamic spectra of the radiation. Type 11 bursts are associated with shock waves propagating through the corona and interplanetary space and radiating from roughly 30 kHz to 1 GHz. Their basic emission mechanisms are believed to be similar to those of type III events and radiation from Earth's foreshock. However, several sub-classes of type II bursts may exist with different source regions and detailed characteristics. Theoretical models for type II bursts are briefly reviewed, focusing on a model with emission from a foreshock region upstream of the shock for which observational evidence has just been reported.

Robinson, P. A.↗
NASA NTRS1987

Models relating the radio emission and ionised gas in Seyfert nuclei

Possible models are discussed in which the radio emitting components in Seyfert II nuclei can compress and accelerate the ambient nuclear medium to produce the characteristics of the narrow line region. A first order model, which considers only the expansion of the radio components, is briefly described. However, in many Seyfert nuclei it appears that the linear motion of the radio components is also important. This can result in shock heating of the ambient medium, and if the cooling time is long enough, can lead to a displacement between the radio component and the associated emission lines. This effect may be present in NGC 1068 and NGC 5929 and by considering ram pressure balance and the cooling length it is possible to estimate lobe velocities and ambient densities.

Pedlar, A.↗
NASA NTRS1992

In ecliptic observations of Jovian radio emissions by Ulysses - Comparison with Voyager results

During the Ulysses inbound cruise to Jupiter the Unified Radio and Plasma Wave (URAP) experiment observed a variety of the planet's radio components in the frequency range below 1 MHz. Most of these emissions were already detected by the Voyager Radio Astronomy and Plasma Wave experiments, however, with much less sensitivity and different spectral coverage. These different radio components within the URAP dynamic spectra are identified, and their appearance with the previous Voyager observations are compared.

Lecacheux, A.↗
NASA NTRS1978

Maps of Jovian radio emission at 1412 MHz

Jupiter was observed with the Westerbork Radio Telescope at a frequency of 1412 MHz in December 1977 when it was at its most northerly opposition to the earth. Pictures were obtained of Jupiter in all four Stokes parameters at 24 different rotational aspects of the planet, each integrated over 15 degrees of Jovian rotation. The maps clearly indicate the presence of higher order terms in the dipolar field of Jupiter at distances of approximately 2 Rj from the center. They also show a displacement of the main dipole of 0.119 plus or minus 0.009 Rj from the center of the disk towards longitude 135-145 degree and a displacement of 0.04 plus or minus 0.04 Rj towards the north in agreement with the displacement found by the Pioneer spacecraft. From the data it is estimated that the thermal disk temperature at this frequency is more than 300 K but less than 340 K, which implies an ammonia mixing ratio of approximately 0.0005.

Pater, I. D.↗
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 NTRS1987

X ray and radio emission in solar He-3-rich events

We have examined radio and x ray properties of solar flares associated with a new sample of individually-identified He-3-rich solar-particle events. Given the association between kilometric Type 3 bursts and He-3-rich events, the timing of the radio events is used to identify the related x ray increases. Examination of these events shows correlations among the radio, x ray, and particle parameters. The sense of these correlations is that larger He-3/He ratios occur in smaller flares suggesting that waves required for He-3 enhancement are damped in large, energetic flares.

Reames, D. V.↗
NASA NTRS1986

Decimeter continuum radio emission from a post-flare loop

It is shown how radio observations permitted the estimation of magnetic fields in the postflare loop associated with the May 19, 1979 long-lasting burst. The strongest 20-cm burst source is associated with H-alpha brightening at 20:41 UT. A comparison of spatially-resolved microwave and soft X-ray emission connected with the flare loop event showed that, at the time of maximum 20-cm flux from the source associated spatially with the declining X-ray flare, as much as one-half of the 20-cm flux could be thermal bremsstrahlung from the X-ray postflare groups. It is suggested that this 20-cm burst emission is produced either by a thermal free-free process or by thermal/nonthermal gyroradiation.

Kundu, M. R.↗
NASA NTRS1973

Thermal radio emission from the major planets.

The use of long-wavelength radio measurements of brightness temperature to remotely measure the thermal structure of the atmospheres of the major planets at great depths is discussed. Data are presented which show that the gross features of Jupiter's and Saturn's microwave spectra, as determined from ground based observations, can be explained in terms of thermal emission from ammonia in deep convective atmospheres of He and H2.

Gulkis, S.↗
NASA NTRS1987

Radio emission from RS CVn binaries. II - Polarization and spectral properties

Multiepoch radio observations of circular polarization and spectral characteristics of several close, late-type stellar binaries are reported. The median luminosity of four well-studied systems ranged from 16.2 to 17.1 ergs/s/Hz. For individual systems, the fractional circular polarization decreases with increasing luminosity, particularly at frequencies above 5 GHz. Eclipsing binaries have significantly lower average circular polarization compared with noneclipsing systems. Helicity reversal is almost always observed between 1.4 and 4.9 GHz for systems with high orbital inclination. Comparison with ten years of previously published polarization observations for two RS CVn stellar systems show that the same helicity occurs at a given frequency for a given source, indicating a very stable, large-scale magnetic field geometry. These spectral and polarization characteristics strongly support a model of inhomogeneous gyrosynchrotron emission arising from electrons with power law energy spectra interacting with inhomogeneous magnetic fields.

Mutel, R. L.↗
NASA NTRS1983

The source location of certain Jovian decametric radio emissions

Evidence is presented which supports the concept that certain of the Jovian decametric radio waves originate as northern hemisphere extraordinary mode cyclotron emissions. The wave signals received by Voyager 1 near 10 MHz shortly after the closest approach to Jupiter were found to exhibit cusps in the fringe pattern which can be attributed to Faraday rotation in the Io plasma torus. At nearly the same time, the wave polarization near 1 MHz was found to exhibit a sudden reversal of its rotation sense, indicating that the wave path for those frequencies had also become perpendicular to the magnetic field at the spacecraft. It was determined that the waves came from the northern hemisphere at progressively lower altitudes with increasing frequency, and if the source is assumed to be associated with an L = 6 field line, the emission appears to have occurred near the source cyclotron frequency somewhere in the local midnight sector. The evidence indicates that the source is at the Io flux tube and that the emitted wave mode must have been extraordinary. In addition, the emitted wave polarization must have been substantially noncircular which would require a low plasma density near the source, much like that which occurs with auroral kilometric radiation at the earth.

Calvert, W.↗
NASA NTRS1994

Correlation of far-infrared emission and radio continuum emission along the major axis of edge-on spiral galaxies

Using new High Resolution far-infrared (FIR) images we have determined FIR flux densities, the FIR luminosity, and intensity profiles along the major axis for eight nearby edge-on spiral galaxies. We present spatial comparisons between the FIR profiles in three of the four IRAS Bands (25, 60, 100 microns). We also present direct spatial comparisons between the 60 micron intensity profiles and intensity profiles from 20 cm radio continuum maps with identical resolution (approx. 60 sec) obtained from J. J. Condon. Using these profiles we have evaluated the 60 micron-to-20 cm ratio Q(sub 60) along the major axis for each galaxy and have compared the results to global Q(sub 60) values. This analysis reveals that a considerable amount of complicated structure exists within the disk of spiral galaxies. Closer examination of this disk structure will make it possible to place further constraints on the well known global far-infrared and radio continuum emission correlation.

Heikkila, Bryant↗