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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
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NASA NTRS1995

The Decline of Jupiter's 13-cm Synchrotron Radio Emission During the Year Following the SL-9 Impacts

Measurements of Jupiter's microwave radio emission from 1990 through August 1995 are reported and analyzed to study the rate of decay in the synchrotron radiation following the dramatic increase observed in July 1994 during the week of impacts by fragments of Comet Shoemaker-Levy 9. The observations were made at 2295 MHz as part of the NASA-JPL Jupiter Patrol, a long-term radio astronomy monitoring program begun in 1971. Data from 34-meter and 70-meter antennas at the NASA's Deep Space Communication Complex at Goldstone, CA are used to estimate slope and curvature of plausible 'baselines' for Jupiter's non-thermal flux density over the five-year interval. These 'baseline' estimates are then used to derive decay times for the outburst emission related to the SL-9 impacts.

Jupiter SL-9↗
NASA NTRS1976

Hectometric and kilometric solar radio emission observed from satellites in August 1972

Type II, type III, and continuum solar radio events, as well as intense terrestrial magnetospheric radio emissions, were observed at low frequencies (10 MHz to 30 kHz) by the IMP-6 satellite during the period of high solar activity in August 1972. This review covers briefly the unique direction-finding capability of the experiment, a detailed chronology of the low-frequency radio events, and, where possible, their association with both ground-based radio observations and solar flares. The attempted observation of solar bursts in the presence of intense magnetospheric noise may, as illustrated, lead to erroneous results in the absence of directional information. The problem of assigning an electron-density scale and its influence on determining burst trajectories is reviewed. However, for the disturbed conditions existing during the period in question, it is felt that such trajectories cannot be determined accurately by this method. The capabilities, limitations, and observing programs of present and future satellite experiments are briefly discussed.

Malitson, H. H.↗
NASA NTRS1987

Radio emission from pre-main-sequence stars in Corona Australis

The central region of the Corona Australis molecular cloud surrounding the stars R and TY CrA has been studied using the VLA at 6 cm. Eleven radio sources are detected including five associated with pre-main-sequence objects. The most striking is associated with the near-IR source IRS 7 and shows a complex structure comprising two strong pointlike sources positioned either side of the deeply embedded IR source and two extended lobes of radio emission. The IRS 7 radio source appears to be similar to that associated with Lynds 1551 IRS 5 but has a considerably larger angular size. The other detected sources include the massive pre-main-sequence star TY CrA, the near-IR sources IRS 1 and IRS 5, and the Herbig-Haro object HH 101. The stars R and T CrA were not detected.

Brown, Alexander↗
NASA NTRS1981

Synoptic observations of Jupiter's radio emissions - Average statistical properties observed by Voyager

Observations of Jupiter's low-frequency radio emissions collected over one-month intervals before and after each Voyager encounter are analyzed to provide a synoptic view of the average statistical properties of the emissions. Compilations of occurrence probability, average power flux density, and average sense of circular polarization are given as a function of central meridian longitude, phase of Io, and frequency. The results are then compared with ground-based observations. The necessary geometric conditions and preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be basically the same as those observed in earth-based studies.

Alexander, J. K.↗
NASA NTRS1986

Solar wind control of Jupiter's decametric radio emission

Observations of the solar wind close to Jupiter are compared with the decametric radio emission (DAM), using data recorded by Voyager 1 and Voyager 2 during 1979. The Non-Io DAM, recorded by both spacecraft and combined using the superposed epoch technique, is found to correlate with the solar wind density and velocity, as well as with the interplanetary magnetic field (IMF) magnitude. In agreement with earlier work using ground-based observations, there are indications that the Non-Io DAM is somehow associated with magnetic sector structure although the precise details of the relationship are still not known and it is not clear if this is a fundamental effect or some secondary effect of intercorrelation.

Barrow, C. H.↗
NASA NTRS1987

Energetic interplanetary shocks, radio emission, and coronal mass ejections

The interplanetary shocks which generate detectable low-frequency radio emission, represent as a group, the most energetic shocks produced by the sun. For all interplanetary (IP) shocks which generated so-called IP type II events, the associated solar events involved fast coronal mass ejections (CMEs). In comparison with the set of all CMEs detected by the Solwind coronagraph, the CMEs associated with IP type II events are the most massive and energetic. The majority belong to the structural classes described by the Solwind researchers as 'curved front' or 'halo'.

Cane, H. V.↗
NASA NTRS1988

Detection of C-13O radio emission from C-13-rich carbon stars

A high ratio of C-13O radio emission in the J = 1-0 rotational line has been detected from three mass-losing carbon stars which optical data indicate have high C-13/C12 ratios. Since chemical fractionation, isotope-dependent photodissociation and opacity in the rotational and vibrational lines may not raise significantly the C-13O ratio above the actual C-13/C-12 ratio in these circumstellar envelopes, the relative abundance of C-13 in these stars might be even greater by perhaps a factor of two than previously believed. About 15 percent of all luminous carbon stars are C-13-rich, and these stars may play a significant role in the enhancement in the C-13/C12 ratio that has occurred during the past 4.6 billion years since the formation of the sun.

Jura, M.↗
NASA NTRS1992

Outer heliospheric radio emissions. I - Constraints on emission processes and the source region

Observations by Voyager 1 and 2 of LF radio emissions near 2 and 3 kHz during the interval 1983-1987 while at heliocentric distances from 15 to 27 AU and 11 to 20 AU, respectively, are reported. Constraints on the emission processes and source characteristics are discussed. Minimum Langmuir wave electric fields in the source region, based solely on the kinematics of the radiation processes, lie in the range 1-100 micro-V/m for nominal source and electron beam parameters. Path lengths for fundamental and harmonic emission processes are calculated. The observed levels of radiation can be produced in path lengths and source dimensions smaller than 1 AU provided the participating Langmuir waves have effective temperatures of about 10 exp 17 K. Previous source models for the radiation are discussed.

Cairns, Iver H.↗
NASA NTRS1997

Ulysses and WIND simultaneous observations of the radio emission associated with the 6-7 January 1997 coronal mass ejection

The three dimensional source location of interplanetary type 2 radio bursts is intended to be determined from two spacecraft observations, performed by the radio receivers onboard the WIND and Ulysses spacecraft and associated with the interplanetary coronal mass ejection detected by the large advanced spectrometer coronagraph (LASCO) from the SOHO spacecraft. The intensity time profiles recorded by WIND and Ulysses were compared and their directivity is found to vary from one component of radio emission to another. The three dimensional location was obtained by radio triangulation and was deduced from the direction measured at WIND and the difference of the arrival times measured at both spacecraft. The sensitivity of both determination methods to wave scattering and refraction was discussed.

Hoang, S.↗
NASA NTRS1992

The effect of magnetic topography on high-latitude radio emission at Neptune

Occultation by a local elevation on the surface of constant magnetic field is proposed as a new interpretation for the unusual properties of Neptune high-latitude emission. Abrupt changes in intensity and polarization of this broadband smooth radio emission were observed as the Voyager 2 spacecraft passed near the north magnetic pole before closest approach. The observed sequence of cutoffs with polarization reversal would not occur during descent of the spacecraft through regular surfaces of increasing magnetic field. The sequence can be understood in terms of constant-frequency (constant-field) surfaces that are not only offset from the planet center but are locally highly distorted by an elevation that occults the outgoing extraordinary-mode beam. The required occulter is similar to the field enhancement observed directly by the magnetometer team when Voyager reached lower altitude farther to the west. Evidence is presented that the sources of the high-altitude emission are located near the longitude of the minimum-B anomaly associated with the dipole offset and that the local elevation of constant-B surfaces extends eastward from the longitude where it is directly measured by the magnetometer to the longitude where occultation of the remote radio source is observed. Together, the radio and magnetometer experiments indicate that the constant-frequency surfaces are distorted by an elevation that extends 0.3 rad in the longitudinal direction.

Sawyer, C. B.↗
NASA NTRS1988

A search for radio emission from flare stars in the Pleiades

The VLA has been used to search for radio emission from flare stars in the Pleiades. Two observational strategies were employed. First, about 1/2 sq deg of cluster, containing about 40 known flare stars, was mapped at 1.4 GHz at two epochs. More than 120 sources with flux densities greater than 0.3 mJy exist on the maps. Detailed analysis shows that all but two of these sources are probably extragalactic. The two sources identified as stellar are probably not Pleiades members as judged by their proper motions; rather, based on their colors and magnitudes, they seem to be foreground G stars. One is a known X-ray source. The second observational strategy, where five rapidly rotating flare stars were observed at three frequencies, yielded no detections. The 0.3 mJy flux-density limit of this survey is such that only the most intense outbursts of flare stars in the solar neighborhood could have been detected if those stars were at the distance of the Pleiades.

Bastian, T. S.↗
NASA NTRS1994

Polarization features of solar radio emission and possible existence of current sheets in active regions

We show that it is possible to account for the polarization features of solar radio emission provided the linear mode coupling theory is properly applied and the presence of current sheets in the corona is taken into account. We present a schematic model, including a current sheet that can explain the polarization features of both the low frequency slowly varying component and the bipolar noise storm radiation; the two radiations face similar propagation conditions through a current sheet and hence display similar polarization behavior. We discuss the applications of the linear mode coupling theory to the following types of solar emission: the slowly varying component, the microwave radio bursts, metric type U bursts, and bipolar noise storms.

Gopalswamy, N.↗
NASA NTRS1995

Changes in Jupiter's 13-cm Synchrotron Radio Emission Following the Impact of Comet Shoemaker-Levy-9

Results of an observing program to monitor the synchrotron radio emission from Jupiter's inner radiation belts before, during and after the impact of Comet SL-9 are reported. The observations were made at 2295 MHz as part of the NASA-JPL Jupiter Patrol, a long-term radio astronomy monitoring program begun in 1971. ne data indicate that the intensity of the synchrotron emission at 13 cm wavelength increased by 27 percent within a few days after the comet impacts; the longitudinal beaming curve was distorted during the week of impacts; the magnetic latitude beaming curves flattened after the week of impacts suggesting an increase in the emission at higher magnetic latitudes; and the decay of the enhanced emission is consistent with an exponential with a time constant of approx. 125 days. The reported changes following the SL-9 impact are unprecedented in the 23-year history of the Jupiter Patrol.

Klein, M. J.↗