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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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NASA NTRS1985

Simultaneous observations of hard X-ray and microwave burst sources in a limb flare

Observations of a flare which occurred just behind the west solar limb on 1981 August 3 are reported. A hard X-ray source (20-30 keV) and a microwave source at 5 GHz were observed simultaneously using the Very Large Array and the hard X-ray telescope aboard the Hinotori spacecraft. Both sources were located in the corona, apparently near the tops of two independent coronal arcades or loops. The source may be composed of many thin filaments unresolved by the VLA observations.

Takakura, T.↗
NASA NTRS1986

Radio emission of cataclysmic variable stars

Eight cataclysmic variable stars were observed at 6 cm wavelength using the Very Large Array (VLA). The objects were: CN-Ori, SS-Aur, YZ-Cnc, SU-Uma, Z-Cam, V603-Aql, EM-Cyg, and RZ-Sge. Most of these objects were in optical high stage, but none were detected beyond flux limits between 0.1 and 0.3 mJy.

Fuerst, E.↗
NASA NTRS1986

Infrared astronomy after IRAS

The development of infrared astronomy in the wake of IRAS is discussed. Attention is given to an overview of next generation infrared telescope technology, with emphasis on the Space Infrared Telescope Facility (SIRTF) which has been built to replace IRAS in the 1990s. Among the instruments to be included on SIRTF are: a wide-field high-resolution camera covering the infrared range 3-30 microns with large arrays of detectors; an imaging photometer operating in the range 3-700 microns; and a spectrograph covering the range 2.5-200 microns with resolutions of 2 and 0.1 percent. Observational missions for the SIRTF are proposed in connection with: planetary formation; star formation; cosmic energy sources; active galactic nuclei; and quasars.

Rieke, G. H.↗
NASA NTRS1985

Spaceborne SAR antenna technology and the Shuttle Imaging Radar-B (SIR-B) antenna development

Shuttleborne SAR systems have been developed jointly by NASA and JPL for remote sensing research. NASA initially entered the field of spaceborne imaging in June 1978 with the launch of Seasat. In November 1981 the Space Agency launched the Shuttle Imaging Radar-A (SIR-A) and SIR-B was lifted into orbit in October 1984. One of the key technical developments in this program is the microstrip planar antenna used to synthesize a large array for high ground resolution. This paper discusses the technology development of these spaceborne antennas with emphasis on the Shuttle Imaging Radar-B (SIR-B) system.

Schaeper, H. R. A.↗
NASA NTRS1985

Microwave imaging of a solar limb flare - Comparison of spectra and spatial geometry with hard X-rays

A solar limb flare was mapped using the Very Large Array (VLA) together with hard X-ray (HXR) spectral and spatial observations of the Solar Maximum Mission satellite. Microwave flux records from 2.8 to 19.6 GHz were instrumental in determining the burst spectrum, which has a maximum at 10 GHz. The flux spectrum and area of the burst sources were used to determine the number of electrons producing gyrosynchrotron emission, magnetic field strength, and the energy distribution of gyrosynchrotron-emitting electrons. Applying the thick target model to the HXR spectrum, the number of high energy electrons responsible for the X-ray bursts was found to be 10 to the 36th, and the electron energy distribution was approximately E exp -5, significantly different from the parameters derived from the microwave observations. The HXR imaging observations exhibit some similiarities in size and structure o the first two burst sources mapped with the VLA. However, during the initial burst, the HXR source was single and lower in the corona than the double 6 cm source. The observations are explained in terms of a single loop with an isotropic high-energy electron distribution which produced the microwaves, and a larger beamed component which produced the HXR at the feet of the loop.

Schmahl, E. J.↗
NASA NTRS1986

Is there a black hole in the sky?

The consequences of the hypothesis that a supermassive black hole can serve as a gravitational lens are analytically studied. It is shown that the presence of a black hole could be established by the unique property that it would appear against the microwave background as a black spot with a diameter of 0.1 arcsec or greater. The only instrument capable of either resolving the black spot or at least noticing it as a negative luminosity source is the Very Large Array.

Paczynski, B.↗
NASA NTRS1986

Constraints on extragalactic-jet characteristics from lobe observations

Very Large Array spectral and polarimetric observations of the lobes of luminous, double radio galaxies are discussed. These observations can provide information on the jets responsible for the sources. Spectral steepening is usually observed in the lobes, with the radio spectral index increasing with distance from the hot spot. These data can be used to infer a 'speed of separation' of the hot spot and lobe material. These speeds are in agreement with hydrocode models of jets. Polarimetric observations indicate that in at least some sources, there is an undectably small amount of internal Faraday rotation, indicating upper limits to the thermal-plasma density of a few times 10 to the -5th/cu cm or less. These measurements are also in agreement with the numerical beam models, provided that the beam density is substantially less than that of the background medium. It is concluded that the lobe observations indicate that these sources are powered by light, high-Mach-number beams.

Spangler, S. R.↗
NASA NTRS1986

Jet activity in the symbiotic variable R Aquarii

Low-resolution ultraviolet spectra of the R Aquarii jet have been obtained with the International Ultraviolet Explorer (IUE). The most recent IUE observations indicate the ionization state of the jet is increasing. Subarcsecond, Very Large Array observations of R Aquarii have resolved the radio-continuum structure into discrete parcels of emission that are extended and nearly collinear. R Aquarii provides evidence that indicates stellar jet activity is not unique to objects associated with high-energy emission processes alone. Rather, the nature of the aligned radio-optical features that comprise the R Aquarii jet indicate that directional mass expulsion, in the form of discrete-collimated ejecta, probably reflect a general, underlying, physical process associated with a wide variety of peculiar stellar objects. As such, the R Aquarii jet constitutes a prototype for jet activity in composite or peculiar emission stars.

Michalitsianos, A. G.↗
NASA NTRS1986

VLA feedhorn for Voyager encounter of Neptune

A high gain, low noise corrugated feedhorn was designed and developed by JPL for use in Very Large Array (VLA) antennas, near Soccoro, New Mexico. The new feedhorn will enable the VLA to support the Voyager encounter of Neptune in August of 1989. This will significantly enhance the receiving capability of the United States for that historic event.

Manshadi, F.↗
NASA NTRS1986

Combined ultraviolet studies of astronomical sources

Topics addressed include: Cygnus Loop; P Cygni profiles in dwarf novae; YY Gem; nova shells; HZ Herculis; activity cycles in cluster giants; Alpha Ori; metal deficient giant stars; ultraviolet spectra of symbiotic stars detected by the Very Large Array; time variability in symbiotic stars; blue galaxies; and quasistellar objects with X-ray spectra.

Baliunas, S. L.↗
NASA NTRS1986

Goldstone solar system radar

Information is provided about physical nature planetary surfaces and their topography as well as dynamical properties such as orbits and spin states using ground based radar as a remote sensing tool. Accessible targets are the terrestrial planets: the Earth's Moon, Mercury, Venus and Mars, the outer planets rings and major moons, and many transient objects such as asteroids and comets. Data acquisition utilizes the unique facilities of the Goldstone Deep Space Network, occasionally the Arecibo radar, and proposed use of the VLA (very large array).

Jurgens, R. F.↗
NASA NTRS1986

Radiative transfer in planetary atmospheres

The research effort was concentrated toward comet P/Halley, although observations of other comets including Giacobini-Zinner, Hartley-Good and Thiele were made as opportunities arise. In preparing for the apparition of P/Halley, detailed predictions for the emission in the 18 cm OH transitions were made in order to assist observers and to indicate what type of data would be particularly valuable. Likewise, since occultations by the comet of background radio sources can provide unique types of information, the tracks of P/Halley and P/Giacobini-Zinner were surveyed with the NRAO Very Large Array, background sources were mapped, and a catalogue of occulted sources published. Beginning in September, 1985, regular observations of the 18 cm OH lines have been made for P/Halley using the 43 m antenna of the NRAO in Greenbank, West Virginia. These data promise to provide the most accurate time sequence for the OH emission for any comet ever obtained at radio wavelengths. From the linewidth and shape, information is obtained on the kinetics of the gas in the cometary coma. An extensive series of observations have been undertaken with 14 m antenna to study emission from the HCN molecule in P/Halley. These data provide the first definitive detection of this component of the cometary ices. Interesting variations in the production of HCN were observed with time scales less than a day. Likewise, there appeared to be variations in the ratio of the hyperfine components of the J = 1-0 transition.

Irvine, W. M.↗
NASA NTRS1986

Passive microwave remote sensing of the asteroids using the VLA: Continuation

The structure and composition parameters for a selected set of the main belt asteroids were inferred by employing microwave remote sensing techniques developed for Earth observations. Precise flux density measurements made with the Very Large Array (VLA) and the 11 m mm-wave antenna of the National Radio Astronomy Observatory are used to define the microwave continuum spectra of these asteroids. These spectra were inverted in order to estimate the near-surface bulk properties (radii, roughness, composition) independent of previous optical or infrared spectroscopy.

Webster, W. J., Jr.↗
NASA NTRS1986

International Halley Watch: Discipline specialists for radio science

Some 34 radio observatories in 18 countries are participating in the Radio Science Net of the International Halley Watch. Approximately 100 radio astronomers are contributing to this effort, which has included observations of comets P/Crommelin and P/Giacobini-Zinner as well as P/Halley. It is clear that the record of data for the 18 cm OH ground state lambda doublet, which provides fundamental information on the gas production rate, kinematics, and potentially the magnetic field in the coma, will be vastly more complete and of higher accuracy than has even been obtained on any previous comet. The coverage by a number of radio observatories will enable short period variations to be studied and correlated with simultaneous data obtained at other wavelengths. Likewise, the first definitive detection of the important parent molecule hydrogen cyanide in a comet was obtained and is being studied by groups in the United States, Sweden, and France. The first detection of the comet with the Very Large Array telescope operated by NRAO was achieved and has produced exciting results for the distribution of emission at high angular resolution from the OH radical. At this writing data are still being obtained and being processed, and there are still strong indications that exciting information will be obtained from radar studies of P/Halley and from searches for additional parent molecules.

Irvine, W. M.↗
NASA NTRS1986

High resolution observations of the L1551 bipolar outflow

The nearby dark cloud Lynds 1551 contains one of the closest examples of a well-collimated bipolar molecular outflow. This source has the largest angular size of any known outflow and was the first bipolar outflow to be detected. The outflow originates from a low-luminosity young stellar object, IRS-5. Optical and radio continuum observations show the presence of a highly collimated, ionized stellar wind orginating from close to IRS-5 and aligned with the molecular outflow. However, we have little information on the actual mechanism that generates the stellar wind and collimates it into opposed jets. The Very Large Array (VLA) observations indicate that the winds originate within 10(15) cm of IRS-5, unfortunately at a size scale difficult to resolve. For these reasons, observations of the structure and dynamics of the hypersonic molecular gas may provide valuable information on the origin and evolution of these outflows. In addition, the study of the impact of the outflowing gas on the surrounding molecular material is essential to understand the consequence these outflows have on the evolution and star formation history of the entire cloud. Moriarty-Schieven et al. (1986) obtained a oversampled map of the CO emission of a portion of both the blueshifted and redshifted outflows in LI551 using Five College Radio Astronomy Observatory 14 m telescope. The oversampled maps have been reconstructed to an effective angular resolution of 20 arcsec using a maximum entropy algorithm. A continuation of the study of Moriarty-Schieven et al. is presented. The entire L1551 outflow has now been mapped at 12 arcsec sampling requiring roughly 4000 spectra. This data has been constructed to 20 arcsec resolution to provide the first high resolution picture of the entire L1551 outflow. This new data has shown that the blueshifted lobe is more extended than previously thought and has expanded downstream sufficiently to break out of the dense molecular cloud, but the redshifted outflow is still confined within the molecular cloud. Details of the structure and kinematics of the high velocity gas are used to test the various models of the origin and evolution of outflows.

Snell, R.↗
NASA NTRS1986

A compact density condensation around L1551-IRS 5: 2.7mm continuum observations with 4" resolution

The dark cloud L1551 contains the best known examples of bipolar molecular outflow. Such outflows are assumed to be driven by winds from young stars embedded in a cloud but the mechanism for collimation of the outflows is still in doubt, though it has been much debated. Among the possibilities put forth to date are intrinsically anisotropic stellar winds, isotropic stellar winds collimated by interstellar toroidal shaped clouds on the order of 10(17) cm in size, or circumstellar disks of order 10(15) cm in size. Because the outflow in L1551 as revealed by the Very Large Array (VLA) cm continuum observations is collimated even at the arc second level it seems as though the stellar wind powering the outflow must either be initially anisotropic or be collimated by something very close to the star, such as a circumstellar disk. We have observed L1551 in the continuum at 2.7 mm with the OVRO millimeter-wave interferometer in the winter of 1983-4 and again, more extensively, in 1985-6. The resulting map shows for the first time direct evidence for a density condensation capable of collimating an initially isotropic flow from IRS 5. This map made from data taken in 1985-6 with projected baselines up to 100 m in length (37k lambda). It has been cleaned and reconstructed with a 4'' gaussian beam. It shows a nearly unresolved source with a suggestion of extension at the 3'' level (assuming a gaussian source shape). The integrated flux density in this map is 170 mJy. A composite spectrum of L1551 is presented which shows that the flux at 2.7 mm is due to the thermal radiation from dust that is also seen at shorter wavelengths. Very little of it can be due to the continuation of the nearly flat cm wavelength spectrum which is assumed to be from thermal bremsstrahlung radiation. The map and spectrum provide strong constraints on the size, temperature, and optical depth of the density condensation surrounding IRS 5.

Keene, J.↗
NASA NTRS1986

The asymmetric profile of the H76 alpha line emission from MWC349

MWC349 is an emission-line star found by Merrill, Humason and Burwell (1932). Braes, Habing and Schoenmaker (1972) discovered that it is a strong radio source. The radio emission originates in a massive ionized wind that is expanding with a velocity of about 50 km s(-1). Its continuum spectrum fits well a nu(0.6) power law from the cm wavelengths to the far-IR. Radio recombination line emission from the envelope of MWC349 was first detected by Altenhoff, Strittmatter and Wendker (1981). We have obtained good signal-to-noise ratio, Very Large Array observations of the H76 alpha radio recombination line from the ionized wind of MWC349. Our data reveal that the profile is markedly asymmetric, with a steep rise on the blue side. This asymmetry could be due to non-LTE effects in the formation and transfer of the line or to intrinsic asymmetries in the envelope. Our analysis suggests that most probably the peculiar profile is caused by a non-LTE enhancement of the line emission from the side of the envelope nearer to the observer. This asymmetry has the opposite sense than that observed in optical and IR recombination lines, where a different effect (absorption of the stellar continuum by the gas in the wind between the star and the observer) is known to be dominant, leading to the classic P Cygni profile. We propose that the profiles of the radio recombination lines from ionized stellar winds will have this characteristic shape, while optical and IR recombination lines are characterized by P Cygni-like profiles. Unfortunately, at present the detection of radio recombination lines from ionized stellar winds is only feasible for MWC349 and a few other objects.

Rodriquez, L. F.↗
NASA NTRS1986

The bird: A pressure-confined explosion in the interstellar medium

The non-thermal radio continuum source G5.3-1.0, mapped at 20 cm with the Very Large Array (VLA) by Becker and Helfand, has an unusual bird-like shape. In order to determine possible interaction of this source with adjacent cold gas, we have mapped this region in the J=1-0 line of CO using the AT and T Bell Laboratories 7m antenna and the FCRAO 14m antenna. The map shown contains 1859 spectra sampled on a 1.5 arcminute grid; each spectrum has an rms noise of 0.2 K in 1 MHz channels. There are several molecular clouds at different velocities along the line of sight. The outer regions of a previously unknown Giant Molecular Cloud (GMC) at l=4.7 deg., b=-0.85 deg., v=200 km s(-1) appears to be interacting with G5.3-10: the molecular cloud has a bird-shaped hole at the position of the continuum source, except that the brightest continuum point (the bird's head) appears to be embedded in the cloud. The velocity of this GMC indicates it is within 2 kpc of the galactic center. The morphology suggests that a supernova or other explosive event occurred near the outside of the GMC, in a region where (n) is approximately 300 cm(-3), and expanded into a region of lower density and pressure. The pressures, densities, and velocity gradients of molecular clouds near the galactic center are on average higher than those of clouds near the Sun. We therefore expect that Type II supernovae near the galactic center would be distorted by their interactions with their parent molecular clouds.

Lane, A. P.↗