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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

183 GHz water line variation: An energetic outburst in orion KL

Observations of the 3(13)-2(20) transition of water vapor in the direction of Ori MC1 in 1980 February show a 50% flux increase and an apparent additional red shift of approximately 2 km/s relative to the line observed in 1977 December. From a detailed examination of the amplitude and frequency calibration, it appears unlikely that the effect is due to systematic error. The increase is attributed to the appearance of a new component at a velocity of 12 km/s with respect to the local standard of rest. The new component also has broad wings. Increased emission from a region in the high-velocity core of Ori MC1 can be due either to additional far-IR radiation to pump the 1983 GHz transition or to a change in the physical conditions in the gas. Statistical equilibrium calculations using the large-velocity-gradient formalism were carried out to develop a model for the emission. The calculations support a model in which the gas in the region of enhanced emission is hotter than the dust. The temporal coincidence between the 183 GHZ increase and the 22 GH1 water maser outburst suggests a common, impulsive cause, which has heated the gas in a part of the HV source, enhancing the emission in both transitions.

Kuiper, T. B. H.↗
NASA NTRS1984

Availability of the DSN Telemetry Data System and Its Major Elements, Including the TWM Assemblies

The DSN discrepancy report system which records all outages of DSN data systems that occur during mission support operations is described. The recorded outages of the telemetry data system for 1981 through 1983 were tabulated and availability characteristics of the telemetry data system and several of its major elements, including the traveling wave maser (TWM) Assemblies were developed. Availability characteristics of the TWM assemblies are compared with those of other DSN subsystems and assemblies. It is found that for a three year period, the availability of the telemetry data system is 99.0%, and its mean time to restore service is 0.9 hours; the availability of the TWM assemblies is 99.83%, and their mean time to restore service is 2.5 hours.

Stevens, R.↗
NASA NTRS1983

Radio emission from AM Herculis - The quiescent component and an outburst

The VLA has been used to search for radio emission from the AM Her-type binaries VV Pup, EF Eri, PG 1550 + 191, CW 1103 + 354, and AN UMa, at 4.9 GHz. A remarkable 10-min outburst was detected from AM Her at 4.9 GHz, which was about 20 times more intense than the quiescent emission and was essentially 100 percent circularly polarized. It is suggested that the quiescent emission of AM Her can be accounted for by 500-keV electrons trapped in the magnetosphere of the white dwarf, provided that the electron energy spectrum is quite hard and that the spectral hardness or number density of energetic electrons increases with radius, while the outburst is probably due to an electron-cyclotron maser operating near the surface of the red dwarf companion. The implied existence of a 1000-gauss localized magnetic field and a corona on the red dwarf has consequences for mass transfer, field line interactions, and variable activity.

Dulk, G. A.↗
NASA NTRS1983

Large-scale anisotropy at centimeter wavelengths

Intrinsic effects in the case of large-scale anisotropy measurements could possibly provide much information about the early universe. Techniques for experimental investigations at centimeter wavelengths are discussed, taking into account the basic problem to measure the difference in the radiation temperature form two directions in the sky with an accuracy of better than 0.0001 K. The largest anisotropy in the 2.7 K background radiation is a dipole distribution, most of which is due to the sun's velocity with respect to the radiation frame. It is pointed out that two very recent results how good agreement with older dipole data. A cooled 3 mm mixer radiometer and a 1.2 cm maser radiometer were flown in balloon. The results of a search for evidence of a quadrupole distribution in the 2.7 K radiation are also reported.

Wilkinson, D. T.↗
NASA NTRS1983

Response of the mobile VLBI design to error sources

The response of Mobile VLBI design to error sources is addressed. The sensitivity of the hydrogen maser to variations in ambient temperature is discussed, with an example of drifts in the frequency system causing excursions in the time-delay observable exceeding + or - 200 cm. It is shown that baselines determined only from S-band data can contain errors in excess of 30 cm during periods of high ionospheric activity. The effect of the troposphere on baseline solutions is examined by comparing calibrations from the Water Vapor Radiometer (WVR) to those from a surface model. The apparent ability of the WVR to track relatively short-period fluctuations in water vapor is noted. Finally, consideration is given to the effects of source structure and the technique of monitoring closure of the time-delay observable around a closed figure of baselines.

Trask, D. W.↗
NASA NTRS1983

Frequency standards for VLBI, present and future

During the last several years, J.P.L. has evaluated a number of different types of frequency standards. These evaluations include measurement of environmetal susceptibilities (barometric pressure, humidity, temperature and magnetic field) and evaluation of stability. Data from these tests are presented for quartz oscillators, rubidium vapor standards, cesium beam standards, hydrogen masers (active and passive) and a superconducting cavity stabilized oscillator. Data on reliability and mechanical ruggedness based on actual field use is also presented. A survey of new frequency standards, their likely performance and environmental characteristics is presented.

Sydnor, R. L.↗
NASA NTRS1983

Precise spacecraft tracking using VLBI digital tone extraction for the purpose of gravitational wave detection

The prospect for the detection of a cosmic background of gravitational wave radiation is discussed. Experiments utilizing precise Doppler tracking of interplanetary spacecraft for the purpose of detecting this background are reviewed. Results of a recent experiment are presented which used facilities of NASA's Deep Space Tracking Network and Owens Valley Radio Observatory to track the Voyager spacecraft in an ultra precise manner using two independent hydrogen masers as frequency standards. The present limiting sensitivity of these experiments are believed to be tropospheric and plasma variations affecting the X band microwave signals at periods of between 1,000 - 10,000 seconds duration.

Anderson, A. J.↗
NASA NTRS1983

Emissions of second-harmonic auroral kilometric radiation

The cyclotron maser theory of Wu and Lee (1979) is used in treating second-harmonic auroral kilometric radiation (AKR). Good agreement is obtained with the ISIS 1 observation reported by Benson (1982). It is found that when the ratio of the electron plasma frequency to the electron gyrofrequency is less than 0.3, the fundamental AKR prevails over the second-harmonic AKR. When the value of this ratio is greater than or approximately equal to 0.3, the fundamental AKR may become weaker than the second-harmonic AKR, and when it is greater than 0.3 the fundamental AKR may diminish. It is also found that the second harmonic AKR with frequencies below twice the electron gyro-frequency can propagate downward.

Wu, C. S.↗
NASA NTRS1984

Relativistic dispersion and the generation of auroral kilometric radiation

Under the conditions at which auroral kilometric radiation (AKR) is known to be produced by a plasma sheet electron region, relativistic effects of the dispersion of extraordinary-mode waves near the electron cyclotron frequency are found to be very significant. The application of linear theory and computer simulation to a model distribution indicates that an extraordinary mode of a particular Reynolds number dominated the radiation emission due to the cyclotron maser instability, suggesting that hot electrons determine the propagation characteristics of AKR and that larger growth rates are possible for direct amplification of extraordinary waves in the auroral region than had been predicted by calculations employing cold plasma dispersion.

Pritchett, P. L.↗
NASA NTRS1984

Infrared observations of dust cloud structure in young R associations - NGC 1333, S68, and NGC 7129

Infrared photometry is presented from 1 to 100 microns of the major sources of luminosity in three regions of star formation which contain young B and A, but not O, stars. The reflection nebulae in all three regions are sources of 100-micron emission similar to previously observed optical reflection nebulae. All three regions also contain highly obscured sources which are often associated with radio maser activity, high-velocity gas outflows, and unusual radio continuum emission. There is a strong correlation between the occurrence of these radio phenomena and the presence of dust close enough to the central objects to radiate strongly in the 3-20 micron spectral region. These obscured sources are likely to be the pre-main-sequence counterparts to the nearby visible main-sequence stars; the obscured objects may still be undergoing mass accretion.

Wilking, B. A.↗
NASA NTRS1984

183 GHz water line variation - An energetic outburst in Orion KL

Observations of the 3(13)-2(20) transition of water vapor in the direction of Ori MC1 in 1980 February show a 50 percent flux increase and an apparent additional red shift of approximately 2 km/s relative to the line observed in 1977 December. From a detailed examination of the amplitude and frequency calibration, it appears unlikely that the effect is due to systematic error. The increase is attributed to the appearance of a new component at a velocity of 12 km/s with respect to the local standard of rest. The new component also has broad wings. Increased emission from a region in the high-velocity core of Ori MC1 can be due either to additional far-IR radiation to pump the 1983 GHz transition or to a change in the physical conditions in the gas. Statistical equilibrium calculations using the large-velocity-gradient formalism were carried out to develop a model for the emission. The calculations support a model in which the gas in the region of enhanced emission is hotter than the dust. The temporal coincidence between the 183 GHz increase and the 22 GH1 water maser outburst suggests a common, impulsive cause, which has heated the gas in a part of the HV source, enhancing the emission in both transitions.

Kuiper, T. B. H.↗
NASA NTRS1986

Intense Source of Polarized Hydrogen Atoms

Atoms produced by radio-frequency dissociation of hydrogen molecules sorted according to their hyperfine states in improved polarized hydrogen source. By use of combination of dc magnetic fields, atoms of upper hyperfine ground level selected in numbers greater than those of undesired F = O state. Source built with permanent magnets or electromagnets. Principal utility is source of polarized hydrogen for masers or experimental studies.

Maleki, L.↗
NASA NTRS1984

The QUASAT mission: An overview

The QUASAT VLBI mission to provide images of the total intensity and polarized emission of compact radio sources in continuum and line with a combination of angular resolution and quality unattainable from Earth is summarized. The astrophysical goals encompass the study of active nuclei at scales appropriate to the outer reaches of accretion disks and the optical broad and narrow line regions; the study of galactic continuum sources in stars and in the galactic center; and spectroscopic studies of galactic and extragalactic molecular masers to determine their role in the life cycle of stars, and their use as direct distance indicators.

Schilizzi, R. T.↗
NASA NTRS1985

QUASAT: An orbiting very long baseline interferometer program using large space antenna systems

QUASAT, which stands for QUASAR SATELLITE, is the name given to a new mission being studied by NASA. The QUASAT mission concept involves a free flying Earth orbiting large radio telescope, which will observe astronomical radio sources simultaneously with ground radio telescopes. The primary goal of QUASAT is to provide a system capable of collecting radio frequency data which will lead to a better understanding of extremely high energy events taking place in a variety of celestial objects including quasars, galactic nuclei, interstellar masers, radio stars and pulsars. QUASAT's unique scientific contribution will be the increased resolution in the emission brightness profile maps of the celestial objects.

Jordan, J. F.↗
NASA NTRS1985

First results of GPS time transfer to Australia

A Global Positioning System time transfer unit built by NBS under contract to JPL was installed at Tidbinbilla Deep Space Communications Complex of the NASA Deep Space Network in June 1983. It has been used to estimate the relationship to UTC(USNO MC) of the Tidbinbilla frequency and time system TID(FTS) based on a hydrogen maser, and thence to estimate the performance of the Australian free-running time scale UTC(AUS). Data from the first three months has been analyzed three ways: by two-hop common view using JPL as intermediary; by long-arc interpolation of measurements against space vehicle clocks; and by long-arc interpolation of GPS-Time results. Residuals from a single quadratic fit through three months of UTC(USNO MC) - TID (FTS) results were white noise with standard error 15 ns, and a flying clock measurement gave 70 ns agreement. A straight line fit through results UTC(USNO MC) - UTC (AUS) gave 90 ns standard error and 120 bns agreement. It is proposed to use the GPS measurements to steer UTS(AUS) to UTC(BIH), and to rename the existing time scale TA(AUS).

Luck, J. M.↗
NASA NTRS1984

Prospects for atomic frequency standards

The potentialities of different atomic frequency standards which are not yet into field operation, for most of them, but for which preliminary data, obtained in laboratory experiments, give confidence that they may improve greatly the present state of the art are described. The review will mainly cover the following devices: (1) cesium beam frequency standards with optical pumping and detection; (2) optically pumped rubidium cells; (3) magnesium beam; (4) cold hydrogen masers; and (5) traps with stored and cooled ions.

Audoin, C.↗