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At least 1,747 records · Page 97
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NASA NTRS1984

1983 lightning, turbulence, wind shear, and Doppler radar studies at the National Severe Storms Laboratory

As part of continuing research on aviation related weather hazards, numerous experiments were incorporated into the 1983 Spring Observation Program. This year's program was an abbreviated one because of commitments made to the development of the Next Generation Radar (NEXRAD) project. The National Oceanic and Atmospheric Administration's (NOAA) P-3 Orion and the National Aeronautics and Space Administration's (NASA) RB-57B and U-2 were the main aircraft involved in the studies of lightning, wind shear, turbulence, and storm structure. A total of 14 flights were made by these aircraft during the period of May 16 through June 5, 1983. Aircraft instrumentation experiments are described, and resultant data sets available for research are detailed. Aircraft instrumentation and Doppler radar characteristics are detailed.

Lee, J. T.↗
NASA NTRS1984

The distribution and abundance of interstellar C2H

C2H(N = 1-0) emission has been extensively observed in a variety of molecular clouds, including: 12 hot, dense, cloud cores, 3 bright-rimmed clouds (in NGC 1977, IC 1396, and IC 1848), and across the extended OMC - 1 cloud. It has also been observed in the circumstellar envelopes IRC + 10216 and AFGL 2688. Abundance analyses of the molecular clouds yield C2H/(C-13)O abundance ratios of about 0.01, with little variation (less than about a factor of 4) either between clouds or across individual clouds. In the Orion plateau source, the C2H abundance is enhanced by less than a factor of 4, relative to the extended cloud. The generally high levels of C2H found in the molecular clouds are not readily accounted for by simple, steady-state chemical models, and suggest, as do earlier observations of atomic carbon, that the carbon chemistry in dense clouds is more active than is commonly assumed.

Huggins, P. J.↗
NASA NTRS1984

The Kleinmann-Low nebula - An infrared cavity

High resolution 20-30 micron IR continuum emission observations of the Orion-KL region, combined with the recent 3.8-micron polarization results of Werner et al. (1983), yield a self-consistent model of the central 30 arcsec of the nebula. In this model, the geometry of the KL nebula is that of a clumpy cavity rather than that of a number of isolated objects. The cavity is centered on IRc2, which is confirmed to be the source of nearly all the region's luminosity. The model which best fits all the IR and radio data implies that the other peaks in th KL nebula are irregularities in the material at the edge and surrounding the cavity, rather than individual self-luminous sources.

Becklin, E. E.↗
NASA NTRS1984

The chemical composition of interstellar molecular clouds

Quantitative molecular abundances are becoming available for dense interstellar clouds and circumstellar envelopes, revealing both similarities across a wide range of source conditions and significant differences in the chemistries involved. As understanding concerning the processes that lead to particular compositions increases, it may become possible to relate these findings to the evolution of molecular clouds and hence to the chemistry of regions in which stellar and planetary formation is in progress. Attention is given to the results of a recently completed spectral scan of the Orion molecular cloud, as well as the envelope around the evolved star IRC + 10216, published by Johansson et al. (1983).

Irvine, W. M.↗
NASA NTRS1984

The millimeter and submillimeter laboratory spectrum of methyl formate in its ground symmetric torsional state

Over 200 rotational lines of methyl formate in its ground (v sub t = 0), symmetric (A) torsional state have been measured in the frequency range 140-550 GHz. Analysis of these and lower frequency transitions permits accurate prediction (below 0.1 MHz) of over 10,000 transitions at frequencies below 600 GHz with angular momentum J lower than 50. The measured spectral lines have permitted identification of over 100 new methyl formate lines in Orion.

Plummer, G. M.↗
NASA NTRS1983

The chemical composition of the pre-solar nebula

The chemical composition of comets may reflect an origin in the molecular cloud which subsequently formed the solar nebula. The chemistry of different types of interstellar clouds is contrasted, including an inventory of molecular species detected in Orion and in TMC 1. The first astronomical detections of the J = (1-0) transition of HCS(+) and the J = (16-15) transition of HC5N and the first detection of SO2 in a cold dust cloud are reported.

Irvine, W. M.↗
NASA NTRS1985

Far-infrared line emission from the galaxy

The diffuse 157.74 micron (CII) emission from the Galaxy was sampled at several galactic longitudes near the galactic plane including complete scan across the plane at (II) = 2.16 deg and (II) = 7.28 deg. The observed (CII) emission profiles follow closely the nearby (12)CO (J=1to0) emission profiles. The (CII) emission probably arises in neutral photodissociation regions near the edges of giant moleclar clouds (GMC's). These regions have densities of approximately 350 cm(-3) and temperatures of approximately 300 K, and amount to 4x10(8) solar mass of hydrogen in the inner Galaxy. The total 157.74 micron luminosity of the Galaxy is estimated to be 6x10(7) solar luminosity. Estimates were also made of the galactic emission in other far-infrared (FIR) cooling lines. The (CII) line was found to be the dominant FIR emission line from the galaxy and the primary coolant for the warm neutral gas near the galactic plane. Other cooling lines predicted to be prominent in the galactic spectrum are discussed. The 145.53 micron (OI) emission line from the Orion nebula was also measured.

Stacey, G. J.↗
NASA NTRS1984

The Lear Jet Observatory: Fifteen Years of Discovery and Rebirth

Some of the highlights of far-infrared spectroscopy are outlined. The scientific discussion is supplemented with a few asides into technology developments. A personal look at the discovery of a particular spectral line in Orion from the Lear jet observatory is given. The rebirth of the Lear facility in time for the 1985 to 1986 apparition of Halley's comet is summarized.

Russell, R. W.↗
NASA NTRS1984

First Results of Submillimeter Polarimetry

Airborne results of submillimeter polarization at one wavelength, 270 micro m for just three points in the sky are presented. Polarizations of 1.7% at each of two points in Orion are shown. A null result at 400 micro m from ground-based observations of Mars at opposition is also presented. A null result for W3(OH) is given. The Kleinmann-Low Nebula (KL) was chosen for one of the measurements because it is bright and polarization had been observed 10 micro m. Airborne results of submillimeter polarimetry indicate that: (1) Cool, dense interstellar clouds can emit polarized submillimeter radiation; (2) The direction of the magnetic field, averaged over the 90 beams, is the same for the Kleinmann-Low Nebula and the 400 micro m peak 1.5 south of the Nebula; and (3) The effectiveness of the grain alignment mechanism, averaged over the 90 beams, is the same for the Kleinmann-Low Nebula and the 400 micro m peak.

Hildebrand, R. H.↗
NASA NTRS1985

Molecular spectroscopy from the Kuiper Airborne Observatory

Interstellar and circumstellar molecules are investigated through medium-resolution infrared spectrosocpy of the vibration-rotation and pure rotational transitions. A primary goal was the construction and improvement of instrumentation for the near and middle infrared regions, wavelengths between 2 and 10 microns. The main instrument was a cooled grating spectrometer with an interchangeable detector focal plane which could be used on the Kuiper Airborne Observatory (KAO) for airborne observations, and also at ground-based facilities. Interstellar shock waves were investigated by H2 emission from the Orion Nebula, W51, and the proto-planetary nebulae CRL 2688 and CRL 618. The observations determined the physical conditions in shocked molecular gas near these objects. From these it was possible to characterize the energetic history of mass loss from both pre- and post-main sequence stars in the regions.

Beckwith, S.↗
NASA NTRS1984

Observations of Mesospheric Turbulence by Rocket Probe and VHF Radar, Part 2.4A

Data from the Jicamarca VHF radar and from a Languir probe fine-structure on a Nike Orion rocket launched from Punto Lobos, Peru, have been compared. A single mesospheric scattering layer was observed by the radar. The Langmuir probe detected irregularities in the electron-density profile in a narrow region between 85.2 and 86.6 km. It appears from a comparison between these two data sets that turbulence in the neutral atmosphere is the mechanism generating the refractive index irregularities.

Royrvik, O.↗
NASA NTRS1985

Observations of far-infrared transitions between excited states of OH

In observations of the Kleinmann-Low Nebula were detected of Orion 84.42 and 84.60 micron transitions between the P-2 sub 3/2 and Pi-2 sub 3/2 (J = 5/2) levels of OH with respective fluxes of 1.0 + or - 0.3 to the minus 17th power and 1.4 + or - 0.4 x 10 to the minus 17th power W cm/sq. When compared to 119 micron flux levels of OH and 153 micron flux levels of these radicals by Viscuso, these results suggest appreciable self-absorption of OH line radiation within the Nebula. It is probable that the CO emission due to the J = 31 yields 30 rotational transition at 84.411 micron makes a substantial contribution to the observed 84.42 micron flux, and that it also is at least partially absorbed at the 84.42 micron OH transition frequency. The 88.55 and 88.78 micron (J = 9/2 to 7/2) transitions of CH also were sought, but yielded only to upper limits of 3 x 10 to the minus 18th power W /sq cm each. A search of W3-IRS5 yields upper limits to the 84.42 micron OH and 87.19 micron CO (J = 30 to 29) transitions of 2 x 10 minus 18th power W cm/2.

Viscuso, P. J.↗
NASA NTRS1985

Mass loss rates from protostars and OI(63 micron) shock luminosities

The high-velocity ejection of material from protostars results in a wind shock which may be observable in OI(63 micron) emission. It is shown that for a wide range of conditions, the OI(63 micron) luminosity is proportional to the mass loss rate from the protostar. Application is made to shock OI(63 micron) emission observed around IRc2 in the BN-KL region of Orion.

Hollenbach, D.↗
NASA NTRS1985

Laboratory measurement of the S(9) pure rotation frequency in H2

The S(9) J = 11-9 ground-state transition in H2 is investigated experimentally, applying a 514.5-nm 300-mW single-mode CW Ar-ion laser to probe the stimulated Raman emission of a CH4-air flame pumped by a single-frequency electronically scannable dye laser amplified to 2 MW by a 10-Hz frequency-doubled Nd:YAG laser. An H2 Raman spectrum with an S(9) frequency of 2130.102 + or - 0.004/cm is shown, and the results are found to be consistent with the measurements obtained in the Orion molecular cloud by Knacke and Young (1980 and 1981).

Jennings, D. E.↗
NASA NTRS1985

Detection of radio continuum emission from Herbig-Haro objects 1 and 2 and from their central exciting source

The region in Orion containing HH 1 and HH 2 was observed with the VLA at 20, 6, and 2 cm on several occasions from 1981 to 1984. At lower resolution, four continuum sources were detected. Two of these sources coincide positionally with HH 1 and HH 2. At 6 cm and higher resolution, HH 1 is resolved into at least two components. The emission is probably bremsstrahlung originating in the same region where the visible line emission is produced. This is the first detection of radio continuum from classic Herbig-Haro objects. At a position closely centered between HH 1 and HH 2, an object that can be interpreted as the energy source of the system was detected. The central source spectrum is S(nu) of about nu to the alpha power, where alpha = 0.4 + or - 0.2, suggesting a stellar wind. Finally, the fourth radio continuum source coincides positionally with an H2O maser and is probably excited by an independent star. There is evidence of time variability in its radio flux. No emission was detected from the Cohen-Schwartz (1979) star at the 0.1 mJy level.

Pravdo, S. H.↗
NASA NTRS1985

Submillimeter observations of OH and CH in M42

The 2Pi(1/2) J = 3/2 to 1/2 transitions of OH at 163.12 and 163.40 microns have been detected, and upper limits have been obtained for the 2Pi(3/2) J = 3/2 to 1/2 transitions of CH at 149.09 and 149.39 microns, in observations of the Kleinmann-Low nebula of Orion. The results indicate emission from a gas cloud at a temperature of roughly 1000 K, having thickness of roughly 5 x 10 to the 14th cm with density about 7 million/cu cm and OH abundance of roughly 12 x 10 to the -6th. The OH column density is about 4 x 10 to the 16th/cu cm in the emitting regions. Optical depth effects play a major role in determining the relative strengths of the observed lines.

Viscuso, P. J.↗
NASA NTRS1985

Observation of far-infrared transitions between excited states of OH

Spectra of the Kleinmann-Low nebula in Orion detected the 84.42 and 84.60 micron transitions between the 2Pi(3/2) J = 7/2 and 2Pi(3/2) J = 5/2 levels of OH with respective fluxes of 1 x 10 to the -17th and 1.4 x 10 to the -17th W/sq cm. When compared to the 119 micron flux levels of OH discussed by Watson (1982) and the 163 micron flux levels of OH by Viscuso et al. (1985), these results suggest appreciable self-absorption of OH line radiation within the nebula. The CO emission due to the J = 31 to 30 rotational transition at 84.411 microns makes a substantial contribution to the observed 84.22 micron flux, and is probably at least partially absorbed at the 84.42 micron OH transition frequency.

Viscuso, P. J.↗
NASA NTRS1985

Submillimeter observations of OH and CH in M42

The (sup 2) pi sub 1/2 (J = 3/2 to 1/2) transitions of OH at 163.12 and 163.40 micro m have been detected and upper limits have been obtained for the (sup 2) pi sub 3/2 (J = 3/2 to 1/2) transitions of CH at 149.09 and 149.39 micro m, in observations of the Kleinmann-Low Nebula of Orion. All four flux levels lie between 1 and 1.2 x 10 to the 17th power/sq.cm. The OH lines are bright when compared to the lower, (sup 2) pi sub 3/2 (J = 5/2 to 3/2) fluxes reported and imply that the 119 micro m emission observed is partially self-absorbed. The combined results provide strong constraints. Taken together with existing data on molecular hydrogen and CO and recent data on other OH transition, they suggest OH emission from post-shock regions at temperatures T approx 1000 k, densities approx. 7 x 10 to the 6th powr/cu cm N sub OH approx 80/cu cm optically thick for the (sup 2) pi sub 3/2 (J = 5/2 to 3/2), 119 micro m but only partially self-absorbing in the (J = 7/2 to 3/2), 84 micro m transitions over a Doppler velocity bandwidth of 30 km/sec. The OH column density is N sub OH approx 4 x 10 to the 16th powr/sq cm. in the emitting regions which occupy a fraction of approx 0.1 of a 1' x 1' field of view centered on the Becklin-Neugebauer source. The CO (J = 31 to 30), 84 micro m transition appears to lie sufficiently close to one of the 84 micro m OH line components to be partially absorbed as well, through a Bowen-type mechanism.

Viscuso, P. J.↗