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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 91 records · Page 5
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NASA NTRS1977

New infrared-CO source in M8

A far-infrared map of the M8 region at 69 microns with a 1-arcmin resolution shows an unresolved source 19 arcmin east of the main component. This source is a strong near-infrared emitter, with K = 4.8 and K - L = 2.6 mag. An intense peak in (C-12)O emission (brightness temperature about 36 K) coincides with the new infrared source. Comparison of millimeter-wave and infrared observations suggest that this source is an extremely young compact H II region. Evidence for a depletion of dust opacity inside the H II region is also found.

Wright, E. L.↗
NASA NTRS1977

90-GHz flux-density measurements of variable radio sources

Results are presented for measurements of the flux densities of 10 variable extragalactic sources at 85.2 or 90 GHz, which were made over a period of almost seven years with the NRAO 36-ft millimeter-wave antenna. The primary flux-density calibration standards used include Jupiter, Saturn, Mars, and the small-diameter Galactic source DR 21. Measured flux densities are given as a function of time (in years) for the sources 3C 84, NRAO 150, 3C 120, OJ 287, 4C 39.25, 3C 273, 3C 279, 3C 345, BL Lac, and 3C 454.3. No statistically meaningful flux-density changes during an observing interval (1 to 3 days) are detected for any source, and a high degree of correlation between flux-density variations at 85.2 or 90 GHz and those observed at lower frequencies is found in all 10 sources. Some variations observed at different frequencies in several individual sources are briefly discussed.

Hobbs, R. W.↗
NASA NTRS1978

Contact Whiskers for Millimeter Wave Diodes

Several techniques are investigated for making short conical tips on wires (whiskers) used for contacting millimeter-wave Schottky diodes. One procedure, using a phosphoric and chromic acid etching solution (PCE), is found to give good results on 12 microns phosphor-bronze wires. Full cone angles of 60 degrees-80 degrees are consistently obtained, compared with the 15 degrees-20 degrees angles obtained with the widely used sodium hydroxide etch. Methods are also described for cleaning, increasing the tip diameter (i.e. blunting), gold plating, and testing the contact resistance of the whiskers. The effects of the whisker tip shape on the electrical resistance, inductance, and capacitance of the whiskers are studied, and examples given for typical sets of parameters.

Kerr, A. R.↗
NASA NTRS1977

Detection of interstellar ethyl cyanide

Twenty-four millimeter-wave emission lines of ethyl cyanide (CH3CH2CN) have been detected in the Orion Nebula (OMC-1) and seven in Sgr B2. To derive precise radial velocities from the astronomical data, a laboratory measurement of the rotational spectrum of ethyl cyanide has been made at frequencies above 41 GHz. In OMC-1, the rotational temperature of ethyl cyanide is 90 K (in good agreement with other molecules), the local-standard-of-rest radial velocity is 4.5 + or - 1.0 km/s (versus 8.5 km/s for most molecules), and the column density is 1.8 by 10 to the 14th power per sq cm (a surprisingly high figure for a complicated molecule). The high abundance of ethyl cyanide in the Orion Nebula suggests that ethane and perhaps larger saturated hydrocarbons may be common constituents of molecular clouds and have escaped detection only because they are nonpolar or only weakly polar.

Johnson, D. R.↗
NASA NTRS1978

Detection of the C4H radical toward IRC plus 10216

Four emission doublets in the millimeter-wave spectrum of IRC plus 10216 are identified as successive rotational transitions of the linear butadiynyl radical (C4H). The identifications are made on the basis of the agreement to within about 1 part in 1000 between the observed rotation constant of C4H and the value obtained from a Hartree-Fock calculation. A rough estimate of the amounts of C4H and C3N in the molecular envelope of IRC plus 10216 is given. The results indicate that C4H seems to be the more abundant species by about a factor of 4.

Guelin, M.↗
NASA NTRS1979

The low-noise 115-GHz receiver on the Columbia-GISS 4-ft radio telescope

The superheterodyne millimeter-wave radiometer on the Columbia-GISS 4-ft telescope is described. This receiver uses a room-temperature Schottky diode mixer, with a resonant-ring filter as LO diplexer. The diplexer has low signal loss, efficient LO power coupling, and suppresses most of the LO noise at both sidebands. The receiver IF section has a parametric amplifier as its first stage with sufficient gain to overcome the second-stage amplifier noise. A broad-banded quarter-wave impedance transformer minimizes the mismatch between mixer and paramp. At 115 GHz, the SSB receiver noise temperature is 860 K, which is believed to be the lowest figure so far reported for a room-temperature receiver at this frequency.

Cong, H.-I.↗
NASA NTRS1979

Interstellar methyl mercaptan

Methyl mercaptan (CH3SH) has been identified in Sgr B2 from observations of six lines in its millimeter-wave spectrum. The CH3SH rotational temperature and column density in Sgr B2 are T(rot) = 9 plus or minus 3 K and N = 1.5 plus or minus 0.2 x 10 to the 14th per sq cm, respectively. The CH3SH/CH3OH ratio is apparently not greatly different from the cosmic S/O ratio.

Linke, R. A.↗
NASA NTRS1979

Interstellar isothiocyanic acid

Isothiocyanic acid (HNCS) has been identified in Sgr B2 from millimeter-wave spectral line observations. We have definitely detected three rotational lines, and have probably detected two others. The rotational temperature of HNCS in Sgr B2 is 14 plus or minus 5 K, its column density is 2.5 plus or minus 1.0 x 10 to the 13th per sq cm, and its abundance relative to HNCO is consistent with the cosmic S/O ratio, 1/42.

Frerking, M. A.↗
NASA NTRS1981

Chlorine oxide in the stratospheric ozone layer Ground-based detection and measurement

Stratospheric chlorine oxide, a significant intermediate product in the catalytic destruction of ozone by atomic chlorine, has been detected and measured by a ground-based 204 GHz, millimeter-wave receiver. Data taken at latitude 42 deg N on 17 days between January 10 and February 18, 1980 yield an average chlorine oxide column density of approximately 1.05 x 10 to the 14th/sq cm or approximately 2/3 that of the average of eight in situ balloon flight measurements (excluding the anomalously high data of July 14, 1977) made over the past four years at 32 deg N. Less chlorine oxide below 35 km and a larger vertical gradient than predicted by theoretical models of the stratospheric ozone layer are found.

Parrish, A.↗
NASA NTRS1980

Molecular clouds in Orion and Monoceros

A 1.2-m millimeter-wave telescope has been used to survey CO in the constellations of Orion and Monoceros. Many new molecular clouds have been found. The distribution of molecular material shows two striking characteristics: (1) Most of the molecular clouds in this region appear to be connected by continuous extensions and filaments. To judge from continuity in radial velocity, most of these connections appear to be real, and are not merely the result of projection along the line of sight; (2) There are at least two slender filamentary features longer than 10 deg in angular extent. These filaments may connect the molecular clouds lying well out of the Galactic plane to clouds lying in the plane. Their shape and orientation suggest that magnetic fields may play a role in their evolution. The observed velocity gradients may be explained by accelerated gas flow along the filament.

Morris, M.↗
NASA NTRS1982

Far-infrared rotational emission by carbon monoxide

Accurate theoretical collisional excitation rates are used to determine the emissivities of CO rotational lines for an H2 molecule content of at least 10,000/cu cm, temperature in the range 100-3000 K, and J not more than 60 under the assumption that the lines are optically thin. An approximate analytic expression for the emissivities which is valid in this region is obtained. Population inversions in the lower rotational levels occur for densities of molecular H2 around 1000-100,000/cu cm and temperatures T not more than about 50 K provided photon trapping is unimportant. Interstellar shocks observed edge-on are a potential source of weak millimeter-wave CO maser emission.

Mckee, C. F.↗
NASA NTRS1982

Probing the presently tenuous link between comets and the origin of life

The possibilities of using millimeter-wave technology to probe the subsurface processes of comets to investigate links between cometary materials and the origins of life are explored. It is noted that current theories hold that the necessities for life to begin comprise a fairly uniform temperature, the presence of a solvent to give materials mobility, and the presence of atoms which can form long chains of molecules. Consideration is given to two cometary nuclei models: a core with an equal amount of liquid water and lunar material, and a nucleus with equal amounts of frozen water ice and lunar material. Solutions to the radiative transfer equation for the two models are presented to characterize identifiable emissions using radiometric spectrometer instrumentation on a spacecraft. Particular species such as OH, CN, HCN, and glycine are expected to be detectable if present.

Hobbs, R. W.↗
NASA NTRS1981

433 micron laser heterodyne observations of galactic CO from Mauna Kea

A submillimeter heterodyne radiometer, developed for astronomical applications, uses an optically pumped laser local oscillator and a quasi-optical Schottky diode mixer. The resultant telescope-mounted system, which has a noise temperature less than 4000 K (double sideband) and high frequency and spatial resolution, has been used to detect the J = 6 to 5 rotational transition of carbon monoxide at 434 micrometers in the Orion molecular clouds. The measurements, when compared with previous millimeter-wave data, indicate that the broad carbon monoxide emission feature is produced by an optically thin gas whose temperature exceeds 180 K.

Buhl, D.↗
NASA NTRS1983

Theoretical study of silicon dicarbide

Silicon dicarbide was first observed in 1926 in spectra of cool carbon stars. The carrier of these bands around 5000 A was tentatively identified as SiC2 by Kleman (1956) who produced similar spectra by inserting silicon into the graphite tube of a King furnace heated to over 2500 K. This identification was strengthened by subsequent mass spectral studies which showed SiC2 as a major molecular component of vaporized silicon carbide. The present investigation is concerned with calculations which were initiated in an attempt to understand more recent astronomical observations of unidentified lines in the millimeter-wave region of the spectrum. The calculations were designed to determine the ground state equilibrium structure and to obtain vibrational and rotational constants. Calculations for estimating the positions and structure of low-lying electronic states were also performed. Self-consistent field (SCF) calculations were performed assuming a closed-shell electronic structure analogous to that in C3. Calculations were conducted for symmetric CSiC, and asymmetric SiCC forms.

Green, S.↗
NASA NTRS1983

Laboratory detection of the C3N an C4H free radicals

The millimeter-wave spectra of the linear carbon chain free radicals C3N and C4H, first identified in IRC + 10216 and hitherto observed only in a few astronomical sources, have been detected with a Zeeman-modulated spectrometer in laboratory glow discharges through low pressure flowing mixtures of N2 + HC3N and He + HCCH, respectively. Four successive rotational transitions between 168 and 198 GHz have been measured for C3N, and five rotational transitions between 143 and 200 GHz for C4H; each is a well-resolved spin doublet owing to the unpaired electron present in both species. Precise values for the rotational, centrifugal distortion, and spin doubling constants have been obtained, which, with hyperfine constants derived from observations of the lower rotational transitions in the astronomical source TMC 1, allow all the rotational transitions of C3N and C4H at frequencies less than 300 GHz to be calculated to an absolute accuracy exceeding 1 ppm.

Gottlieb, C. A.↗
NASA NTRS1986

High-resolution mapping of mass loss from highly evolved carbon stars

The molecular component of the mass outflow at high resolution was mapped with the Owens Valley Millimeter-Wave Interferometer in two well-known objects, CRL 2688 and CIT 6. Interferometric observations of a pair of carbon stars which are evolving toward the planetary nebula stage have revealed evidence of episodic, nonspherically symmetric mass loss, and may lead to a fuller understanding of shielding properties of the dust grains involved in these flows.

Ball, R.↗
NASA NTRS1961

Lunar Brightness Variations with Phase at 4.3-MM Wave Length

The lunar radio observations and interpretations of Piddington and Minnett (1949) and Gibson (1958) show that the lunar brightness variation with phase at millimeter wave lengths can be used to determine the physical properties of the lunar surface. They found that the millimeter-wave brightness lagged the optical phase, and their interpretation was that the millimeter radiation originates below a surface layer that is a very good thermal insulator. The thickness of this layer could not be determined from observations at one frequency. Observations at different frequencies give different results because of the wave-length dependence of the radio absorption by the surface material. The attenuation in the material increases with decreasing wave length, and therefore it is possible, in principle, to determine surface layer thickness from radio observations at several wave lengths. For this reason, observations of lunar radiation were started at the Naval Research Laboratory at a wave length of 4.3 mm. This is half the wave length used by Gibson (1958) in his earlier studies. The radio telescope used for these observations has been described in detail in a previous publication (Coates 1958). The antenna is a parabolic reflector 10 feet in diameter, and it has a beam width of 6.7 minutes of arc at the wave length of 4.3 mm. This is about one-fifth the diameter of the moon. The receiver was a Dicke-type radiometer.

Coates, Robert J.↗