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NASA NTRS1992

Observations of stationary radio sources: Coronal polar plumes?

Observations and preliminary results of polar radio sources which are often brighter than streamers are presented. The results are preliminary and an analysis is needed using a larger data set to firmly establish the properties such as time variability of these sources. Data which are not corrected for ionospheric refraction are used, thus the determination of rotational characteristics is not accurate. Thermal and/or weak nonthermal emission from polar plumes may be responsible for the polar radio sources. However, nonthermal process may be necessary to explain time variability.

Gopalswamy, Natchimuthkonar↗

NASA NTRS1992

Blue galaxies identified with submilliJansky radio sources in the 1300 + 3034 field

We have obtained deep B and R CCD frames in order to optically identify sub-mJy radio sources discovered in a deep 1.49 GHz VLA survey field centered at alpha (1950) = 13h00m37s, delta(1950) = + 30 deg 34 arcmin. B and R photometry is presented for 37 optical identifications. Using spectral evolution models, we conclude that galaxies brighter than B about 25 identified with sub-mJy radio sources are much bluer than giant elliptical galaxies, but are similar to starburst galaxies with absolute magnitude M(v) = about -23-20 and redshifts in the range 2 = about 0.1-0.8. This population of blue galaxies is the same as that found by Thuan and Condon (1987) in the 0852 + 1716 field using different techniques (optical and near-infrared photometry), suggesting that this population of starburst galaxies at intermediate redshifts is universal.

Thuan, Trinh X.↗

NASA NTRS1992

Density waves in Saturn's rings probed by radio and optical occultation - Observational tests of theory

A parallel examination is conducted of Voyager radio and photopolarimeter occultation observations of the Saturn A ring's density waves. The radio instrument waves exhibit an average -90 deg offset from the dynamical phase. A warping height of about 100-m amplitude can qualtitatively reproduce this phase shift, while preserving the overall model wave shape. These results may be profoundly relevant for satellite-ring torque calculations in Saturn's rings, given the deposition of all of the net torque of the standard model in the first wavelength.

Brophy, Thomas G.↗

NASA NTRS1992

Pulsed high-energy gamma-rays from the radio pulsar PSR1706-44

Gamma radiation above 100 MeV in energy has been detected from the radio pulsar PSR1706-44. The gamma emission forms a single broad peak within the pulsar period of 102 ms, in contrast to the two narrow peaks seen in the other three known high-energy gamma-ray pulsars. The emission mechanism in all cases is probably the same, the differences arising from the geometry of the magnetic and rotation axes and the line of sight. Gamma-ray emission accounts for as much as 1 percent of the total neutron star spindown energy in these pulsars, much more than emerges at optical or radio frequencies. Thus, study of this emission is important in understanding pulsar emission and evolution.

Thompson, D. J.↗

NASA NTRS1992

Deep Hubble Space Telescope imaging of a compact radio galaxy at z = 2.390

The radio galaxy with the highest redshift in the Leiden-Berkeley Deep Survey, 53W002, is described and examined in terms of UV profile in relation to an early-type galaxy. The HST WFC images have a resolution of 0.2 arcsec FWHM, and the I- and V-band structures are assessed. The source is elongated in a manner similar to the Ly alpha cloud in V, and the structure is highly compact in I. The present object with a young starburst has very high central UV surface brightnesses relative to nearby luminous early-type galaxies, while the light profiles are similar. The data are concluded to suggest that 53W002 is a young galaxy that has a regular light profile at z = 2.390 even though it has been forming stars since not more than about 0.5 Gyr before z = 2.390. Such a scenario is consistent with concurrent dynamical collapse and star formation in the compact radio galaxy.

Windhorst, Rogier↗

NASA NTRS1992

Simultaneous observations of coronal bright points in X-ray and radio wavelengths

We present a first explicit comparison of coronal bright points in soft X-ray and radio wavelengths, using the Soft X-ray Telescope aboard the Yohkoh spacecraft and the Very Large Array. About half of the 33 compact sources identified in a 20-cm full-disk map appear as X-ray bright points in the X-ray data. The other half apparently corresponds to unipolar regions with enhanced magnetic fields. Thus, the identification of radio bright points alone cannot reliably serve as a proxy for X-ray bright points. A preliminary analysis reveals that bright points commonly observed at 20 cm and in X-rays have temperatures of (1.4-2.9) x 10 exp 6 K and emission measures of (0.4-2.5) x 10 exp 45/cu cm. The observed brightness temperatures at 20 cm (1-2.5) x 10 exp 5 K can be explained in terms of optically thin free-free emission from a plasma with these parameters.

Nitta, Nariaki↗

NASA NTRS1993

High-resolution VLBA imaging of the radio source Sgr A* at the Galactic Centre

Images of Sgr* A with milliarcsecond resolution obtained by using five telescopes of the partially completed Very Long Baseline Array (VLBA) in conjunction with a few additional telescopes are presented. The image of Sgr A* at a wavelength of 3.6 cm confirms almost exactly the elliptical Gaussian model that has been proposed on the basis of previous data. The source size at 1.34 cm wavelength is 2.4 +/- 0.2 mas, similar to previous results. At both wavelengths, the radio source is smooth, without detectable fine structure. These observations support the suggestion that the radio emission from Sgr A* is strongly scattered by electron-density fluctuations along the line of sight. On the assumption that the emission is due to a black hole accreting stellar winds from massive stars in the central 0.5 pc, the observations are consistent with a black hole mass of less than about 2 million solar masses.

Lo, K. Y.↗

NASA NTRS1993

Cassini radio and plasma wave investigation - Data compression and scientific applications

The Radio and Plasma Wave Science (RPWS) experiment being built for the Cassini spacecraft will study a wide range of plasma and radio wave phenomena in the magnetosphere of Saturn and will also make valuable measurements during the cruise phase and at other encounters. A feature of data from wave receivers is the capability of producing vastly more data than the spacecraft telemetry link is capable of transmitting back to the Earth. Thus, techniques of on-board data compression and data reduction are important. The RPWS instrument has one processor dedicated to data compression tasks.

Woolliscroft, L. J. C.↗

NASA NTRS1993

Source characteristics and locations of hectometric radio emissions from the northern Jovian hemisphere

Northern Jovian hectometric (HOM) radio emissions, detected from high Jovian latitudes by the Unified Radio and Plasma Wave experiment on the Ulysses spacecraft, were observed at all Jovian longitudes. This emission was observed to be predominantly right-hand circularly polarized, but some left-hand circular polarization was observed implying the presence of O mode emissions from the northern Jovian hemisphere. Intense HOM emissions, with well-defined directions and polarizations, were often confined to similar longitudinal regions where intense HOM emissions were previously observed at low latitudes. The present analysis confirms that these northern HOM sources lie in the Jovian polar regions on magnetic field lines that pass through the Io plasma torus. The observations may be consistent with emission from either a filled cone beam or a longitudinal distribution of thin hollow cones.

Reiner, M. J.↗

NASA NTRS1993

Long-term changes in Jovian synchrotron radio emission - Intrinsic variations or effects of viewing geometry?

Possible causes of the observed long-term variation of Jovian synchrotron radio emission, including both intrinsic changes in the Jovian radiation belts and apparent changes due to variations in the Jovigraphic declination of the earth, D sub E, are investigated. An increase in diffusion rate with other parameters held constant results in an inward displacement of the peak emission radial distance that is not observed. Effects of viewing geometry changes are examined. The possible importance of such effects is suggested by a correlation between the total decimetric radio flux and D sub E, which varies between -3.3 and +3.3 deg during one Jovian orbital period. Because the Jovian central meridian longitudes where the magnetic latitude passes through zero during a given Jovian rotation change substantially with D sub E and since significant longitudinal asymmetries exist in both the volume emissivity and the latitudinal profile of the beam, the total intensity should be at least a partial function of D sub E.

Hood, Lon L.↗

NASA NTRS1993

Observations of (S III) emission from Galactic radio sources - The detection of distant planetary nebulae and a search for supernova remnant emission

Narrow-band near-infrared imaging observations at wavelengths corresponding to forbidden S III 9069,9532 A have been carried out at the MDM 1.3 m telescope for 23 radio sources near the Galactic plane in an attempt to detect emission associated with nebulae marking the endpoints of stellar evolution. While none of the known remnants or remnant candidates were detected, 10 of the 11 PN candidates from a new radio imaging survey of the Galactic plane were clearly seen in the forbidden S III 9532 A line. We present a calculation of the relative efficacy of searching for PNe in the forbidden O III and forbidden S III lines; for the majority of all PNe, the observed forbidden S III 9532 A line is predicted to be stronger than forbiden O III 5007 A whenever the visual extinction exceeds 3 magnitudes. This makes forbidden S III the superior tracer of PNe at distances exceeding a few kpc. We briefly comment on the significance of this approach to defining the spatial distribution of the PN population of the Galaxy.

Kistiakowsky, V.↗

NASA NTRS1993

High-resolution radio observations of the supernova remnant 3C 391 - Possible breakout morphology

We present radio observations of the bright compact SNR 3C 391 (G31.9+0.0) made with the VLA2 at 6 arcsec resolution. The remnant's morphology suggests expansion into a medium with a very strong density gradient. We interpret radio and X-ray morphologies as evidence for a breakout of the expanding material into a region of abruptly lower density. The CO survey of Sanders et al. (1986), though not fully sampled, shows the presence of molecular gas at the position of the remnant, with a radial velocity of 90-110 km/s similar to the highest velocity absorption features seen in H I toward 3C 391. This gas may thus be near the remnant, though direct evidence of interaction is lacking. More detailed CO observations, and searches for evidence of shocked molecular gas such as 2.12 micron emission from H2, might confirm or refute the tantalizing possibility that 3C 391 is interacting with an observable molecular cloud.

Reynolds, Stephen P.↗

NASA NTRS1993

BL Lacertae objects, Fanaroff-Riley type I radio sources, and cluster cooling flows

The correctness of the view that the Fanaroff-Riley type I (F-R I) radio galaxies and the BL Lac objects are intrinsically the same and that the strong emission seen in BL Lac may be the result of beaming of radiation from the galactic nucleus is examined. Expressions are derived for the surface brightness of scattered beams of polarized or unpolarized radiation, and the expected scattered light surface is calculated assuming the beams have spectra and fluxes consistent with those observed for BL Lac objects. The models are compared to recent observations of lobes of excess, polarized blue light in Cy-A, and observations of lobes of UV light in the central regions of the cD galaxies in A1795 and A2597. It was found that the models predict scattered surface brightnesses in reasonable agreement with those observed. If these lobes are indeed scattered light, this would indicate that F-R I radio galaxies do possess beams of radiation with apparent luminosities similar to BL Lac objects and that the radiation is actively beamed and not merely obscured by a torus of dust around the nucleus.

Sarazin, Craig L.↗

NASA NTRS1992

Position and morphology of the compact non-thermal radio source at the Galactic Center

We have determined with VLBI the position of the compact nonthermal radio source at the Galactic Center, commonly referred to as SgrA*, in the J2000.0 reference frame of extragalactic radio sources. We have also determined the size of SgrA* at 1.3, 3.6, and 13 cm wavelengths and found that the apparent size of the source increases proportionally to the observing wavelength squared, as expected from source size broadening by interstellar scattering and as reported previously by other authors. We have also established an upper limit of about 8 mJy at 3.6 cm wavelength for any ultracompact component. The actual size of the source is less than 15 AU. Fourier analysis of our very sensitive 3.6 cm observations of this source shows no significant variations of correlated flux density on time scales from 12 to 700 s.

Marcaide, J. M.↗

NASA NTRS1992

High-precision VLBI astrometry of the radio-emitting star Sigma CrB - A step in linking the Hipparcos and extragalactic reference frames

VLBI observations of the optically bright radio-emitting star Sigma Coronae Borealis (Sigma CrB) have yielded its position relative to an angularly nearby quasar, its annual proper motion and its trigonometric parallax with formal uncertainties slightly better than 0.2 milliarcsec. This is the first result of the VLBI astrometric program we are conducting on 11 radio stars similar to Sigma CrB. We plan to obtain comparable results for all stars when enough epochs of observations are acquired. These stars will be used to astrometrically link the Hipparcos and VLBI extragalactic reference frames.

Lestrade, Jean-Francois↗

NASA NTRS1993

A tight correlation between radio and X-ray luminosities of M dwarfs

We present results of a survey of nonflare radio and X-ray properties of dM/dMe stars. This survey was obtained during the ROSAT All-Sky Survey and is accompanied by mostly simultaneous VLA observations. We find that the X-ray and radio luminosities are correlated over three orders of magnitude, L(R) is proportional to L(X), irrespective of spectral type. This result improves if strictly simultaneous observations are considered. This correlation points to a physical relation between the particle populations responsible for the two emissions.

Gudel, Manuel↗

NASA NTRS1925

The drift of an aircraft guided towards it's destination by directional receiving of radio signals transmitted from the ground

Following a curved path increases the distance to be flown, and a type of radio navigation that forces the adoption of such a path is therefore less efficient than one that marks out a definite straight line between the point of departure and the intended destination, and holds the airplane to that line. To determine the loss of efficiency resulting from curvature of the path, calculations were made for two particular cases by the method of step-by-step integration. The calculations were based on the assumption that the pilot makes straightforward use of his radio for navigation and makes no allowance for drift. Results are given in tabular form for two airplanes flying 200 miles at 100 mph, one with a cross wind of 50 mph wind across course, and the other with a 20 mph wind across course. It is shown that the following of the curved path increases the time of flight and the air distance flown by 17 percent and 2.5 percent in the two cases.

Source record↗

NASA NTRS1994

Dynamics Of Ions In A Radio-Frequency Quadrupole Trap

Report describes computer-simulation study of motions of various numbers of ions in Paul trap. Study part of continuing effort to understand motions of trapped charged particles (atoms, ions, molecules, or dust particles). Motions characterized in terms of heating by radio-frequency fields, formation of crystallike structures in cold clouds of trapped particles, and other phenomena important in operation of radio-frequency traps in frequency standards.

Prestage, John D.↗