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At least 433 records · Page 24
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NASA NTRS1989

Shock chemistry in the molecular clouds associated with SNR IC 443

Observations of several interstellar molecules toward the highly perturbed B and G clouds associated with SNR IC 443 are reported. The results suggest that hot and dense material is present in the SNR, and that shocks are present in both regions. The HCO(+) abundance is shown to be a few times greater that found in cold quiescent gas, in contradiction with previous results. The SO, CS, CN, and NH3 abundances are similar to those found in cold dark clouds.

Ziurys, L. M.↗
NASA NTRS1989

No molecular gas disk in S106

The radio and optical bipolar H II region, S106, is bisected by a dark lane. The premain-sequence object, S106 IR, which is the source of a powerful ionized stellar wind, is the exciting source of this region and is found at the center of the equatorial emission gap. The existence of a massive, extended, molecular gas disk has previously been suggested as an explanation for the peculiar morphology of this source, and S106 has widely been quoted as the best example of theoretically posited accretion disks. The new, high-resolution, CS and (C-13)O observations presented show that the molecular emission, previously attributed to a disk structure, actually originates from distinct masses of molecular gas, swept up from the ambient cloud core by the ionized lobes.

Barsony, M.↗
NASA NTRS1989

Far infrared, submm and mm spectroscopy of the galactic center: Radio arc and +20/+50 km s (exp -1) clouds

The observations of the par improved spectroscopy and the molecular clouds at the galactic center are reported. The results show: the spatial distributions of C(II) 158 microns and molecular line radiation and of the thermal radio continuum emission in the arched filaments of the radio arc are similar; about 2 x 10(exp 4) of the solar mass, or 10 percent of the total gas mass in the radio arc, are contained in C(+) regions; the H(+)/C(+) regions are probably located at the surfaces of the dense molecular clouds in the arc. Profiles, fluxes and spatial distributions of the C(II) fine structure and CO rotational lines are reported. It is demonstrated that the data does not fit models in which the neutral interstellar clouds in the arc are ionized by shocks or by magnetohydrodynamic phenomena. Moreover, that the high temperatures and densities derived previously from NH3 and CS observations may not be characteristic of the bulk of the molecular gas.

Genzel, R.↗
NASA NTRS1989

Sulfur compounds in comets

Cometary atmospheres exhibit abundant sulfur and sulfur compounds, which are absent in planetary atmospheres. Sulfur compounds were also detected in interstellar media, including SO, SO2, CS, etc., but excluding S2 which was identified only in IRAS-Araki-Alcock 1983d. Fluorescence calculations are used to analyze the B-X system of S2 which appeared in IUE and ground-based spectra of IRAS-Araki-Alcock 1983d. Single- and multiple-cycle fluorescence calculations indicate that fluorescent equilibrium accounts for the observed spectra despite the fact that the S2 lifetime against solar ultraviolet radiation is relatively short. This analysis confirms unambiguously that emission peaks in the 3000 to 4000 A spectral range of the ground-based data are due to the B-X bands of S2. New evidence is presented of at least one S2 outburst before it was detected by A'Hearn, Feldman, and Schleicher. The time variation of S2 outgassing rates and discussion on the correlation between solar wind flux and the S2 outbursts will be presented.

Kim, S.↗
NASA NTRS1990

Experiment K-6-08. Biochemical and histochemical observations of vastus medialis

Muscles of the hindlimb in the rat have been used to demonstrate the effects of unloading in weightlessness and in animal models used to mimic weightlessness. The vastus medialis (VM) is discussed here. Samples were obtained from rats exposed to weightlessness for 12 days in Cosmos 1887 (Experiment K-6-08, coordinated by Dr. V.S. Oganov). The principal objective of this study was to ascertain if the vastus medialis responded to 12 days of microgravity exposure. The loss in muscle mass is greatest, -43 percent, when comparing F vs B, and least, -13 percent, when comparing F vs. V. Taken at face value these differences may be misleading. Due to the variability of the muscle weight in the basal group, these muscle mass losses may be exaggerated. In terms of percent water, there were no differences between the flight and the control groups. In spite of the limited sample, researchers conclude that muscle mass changes in the VM are not significant. Although some of the morphological parameters suggest a small degree of atrophy in the vastus medialis, the biochemical analyses (protein, RNA and DNA) suggest that these may be minimal and functionally nonsignificant. The relatively similar CS and LDH activities of VM from F and various control groups, as well as the lack of difference in LPL activity between F and S rats, suggests that there is little or no effect on the oxidative or glycolytic function of this muscle. Since the VM is chiefly a mixed fast twitch muscle, these metabolic indices of energy production are relatively unchanged. The results of VM studies are in agreement with previous observations of another type II fast twitch muscle, the EDL, from SL-3 rats which did not respond markedly to weightlessness and whole body suspension.

Musacchia, X. J.↗
NASA NTRS1989

The physics and chemistry of the L134N molecular core

The dark cloud L134N is studied in detail via millimeter- and centimeter-wavelength emission-line spectra. A high-density core of molecular gas exists in L134N which has a kinetic temperature of about 12 K, a peak molecular hydrogen density of about 10 exp 4.5/cu cm, and a mass of about 23 solar. The core may be the site of future star formation. Maps of emission from (C-18)O, CS, H(C-13)O(+), SO, NH3, and C3H2 reveal morphologically different distributions resulting in part from both varying physical conditions within the cloud and optical depth effects. Significant differences also exist which are probably due to chemical abundance variations. A consistent set of LTE chemical abundances has been estimated at as many as seven positions, which can be used to constrain chemical models of dark clouds.

Swade, Daryl A.↗
NASA NTRS1989

Pressure dependence of the melting temperature of metals

A new method for the analysis of the experimental data for the pressure dependence of the melting temperature of metals is presented. The method combines Lindemann's law, the Debye model, and a first-order equation of state with the experimental observation that the Grueneisen parameter divided by the volume is constant. It is observed that, based on these assumptions, in the absence of phase transitions, plots of the logarithm of the normalized melting temperature versus the logarithm of the normalized pressure are straight lines. It is found that the normalized-melting--temperature versus normalized-pressure curves accurately satisfy the linear relationship for Al, Ag, Au, Cs, Cu, K, Na, Pt, and Rb. In addition, this technique provides a sensitive tool for detecting phase transitions.

Schlosser, Herbert↗
NASA NTRS1990

The nature of low-albedo asteroids from 3-micron multi-color photometry

The present broadband and narrowband 1.2-3.5 micron spectrophotometry of 16 low-albedo asteroids encompasses C-, F-, P-, D-, and T-class asteroids, and has been used in an effort to identify low-temperature minerals on their surfaces. Attention has been given to the identification of water of hydration. While G-class asteroids have water-rich surfaces, and I asteroids possess some hydrated silicates, not all class Cs do. Finally, the P-, F-, and T-class asteroids do not seem to possess hydrated-silicate surfaces.

Lebofsky, Larry A.↗
NASA NTRS1990

A spectacular molecular outflow in the Monoceros OB1 molecular cloud

Detailed observations of CO, CS, IR continuum, and H2 emission from a large, highly collimated, bipolar outflow in the Monoceros OB1 molecular cloud are presented. The CO observations suggest that molecular gas in the outflow is contained in a shell with higher velocity material situated interior to lower velocity material. The velocities of outflow emission are found to increase with increasing distance from the center of the outflow. Additional detections include shock-excited molecular hydrogen emission from the blueshifted lobe of the outflow and six 2-micron sources in the direction of the outflow. Near-IR and IRAS observations suggest that the driving source for the outflow must have a bolometric luminosity below about 4.5 solar luminosities. It is concluded that the flow is probably not driven by stellar radiation from a central source.

Margulis, Michael↗
NASA NTRS1990

Geochemistry of Darwin impact glass and target rocks

Results are presented from major and trace element composition analyses of 18 Darwin (Australia) glass samples and seven target rocks from the Darwin crater area. It is found that the chemical composition of the glass samples is in agreement with an origin from terrestrial sediments during an impact. Analyses of the target rocks from the Darwin crater and mixing calculations show that the Darwin glass can be formed from the local target rocks. Evidence is presented for a loss of the volatile elements Ga, Zn, F, and B during the impact event. The elements Na, K, Rb, and Cs show lower abundance in the glass than in the target rocks. This suggests selective volatilization from the impact melt.

Meisel, Thomas↗
NASA NTRS1990

Volatile/mobile trace elements in Bholghati howardite

Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U, and Zn by RNAA are determined in two kinds of material from the Bholghati howardite: a carbonaceous chondrite clast (BH-4) that originated by primary nebular condensation/accretion processes; whole-rock samples and clasts resulting from parent-body processes, especially igneous differentiation. Trace element contents in Bholghati whole-rock (matrix) samples and/or white eucritic clasts in it are high for an achondrite, and variable. These characteristics are indicative of random condensation of volcanic emanations admixed with preexisting eucrite, diogenite, and howardite layers in the HED parent body. Other HED samples show similar patterns, and the conclusion that these reflect extensive volcanism in an asteroidal-sized object is supported by other Consortium noble gas and cosmochronologic measurements.

Wang, Ming-Sheng↗
NASA NTRS1990

Unidentified ions in comets

Optical spectra were taken of comets Halley, West, and Brorsen-Metcalf in the wavelength region 3200 to 6400 A. These spectra were offset approximately 10(exp -5) to 10(exp -6) km tailward from the nucleus so that the features detected were all ions with the exception of a very small residual C2 emission at 5165 A. The full labeled tail spectrum of comet Halley is given. While most of the features detected are attributable to CO(+), H2O(+), CO2(+), CH(+), and OH(+), there are three moderately strong bands in the spectra of comets Halley and Brorsen-Metcalf which remain unidentified. These features were not detected in comet West. All three spectra in the 4800 to 5400 A region are presented, Brorsen-Metcalf is the gassiest of the three. The central wavelengths of the unidentified features are 4930, 5300, and 6000 A. In an effort to identify the ions responsible for these features as well as to confirm previous identifications, laboratory spectra of ions were compared with the comet spectra. H2O(+) and CO(+) are known to have extensive emission in the 4800 to 6200 A region. Therefore, the possibility that these unidentified features are due to H2O(+) and CO(+) was investigated. A search for the following bands was conducted: H2O(+) (11-0), H2O(+) (12-0), H2O(+) (13-1), CO(+) (1-1), and CO(+) (0-0). CO(+) (1-1) and CO(+) (0-0) were previously identified and are present in all the spectra examined. The H2O(+) (11-0) band was identified. Comparison of the H2O(+) (11-0) synthetic spectrum with comet Brorsen-Metcalf data is presented. The relative fluxes of the blended H2O(+) lines in the synthetic spectrum match those of the cometary data. After eliminating H2O(+) and CO(+) as significant contributors to the stronger unidentified features, spectra of ions which are not yet identified in the optical region of comets were compared to the data. These ions are NH(+), CS(+), and C2(+). None of these ions appears to be a significant contributor to the optical spectra of these three comets. In conclusion, H2O(+) (11-0) was unabiguously identified in cometary optical spectra. No other molecular ion for which there are laboratory spectra can explain the unidentified features found in the ion tails of comets Halley and Brorsen-Metcalf.

Engel, Lisa↗
NASA NTRS1990

IUE observations of comet Austin (1989c1)

Observations of comet Austin (1989c1) were made using the International Ultraviolet Explorer (IUE) satellite on December 22, 1989 (preperihelion) and on nine dates between 7 and 24 May, 1990 (postperihelion). A summary of observation dates and parameters is given. The ultraviolet spectrum is characteristic of that of non-dusty comets. Some preliminary results are presented for OH and CS production rates and dust-reflected solar continuum emission based upon the long wavelength, low resolution mode spectra; photometry using the IUE Fine Error Sensor; a detection of the CO fourth positive system in the short wavelength, low dispersion spectra; and an upper limit on S2.

Budzien, S. A.↗
NASA NTRS1990

Submillimeter astronomy and low mass star formation

Surveys made at wavelengths shorter than 100 microns are criticized in that they are biased against finding the coldest, most deeply obscured, and possibly youngest protostars. Large scale mapping of star forming regions in the submillimeter continuum and in lines such as CS H2CO and NH3, that are excited at high density, is identified as crucial in order to find clouds in the earliest stages of collapse into stars. The use of photometry from 1 to 1000 microns in characterizing the disks around embedded stars and T Tauri stars is outlined.

Beichman, Charles A.↗
NASA NTRS1990

The classical microwave frequency standards

Some key problems are presented encountered in the classical microwave frequency standards which are still not solved today. The point of view expressed benefits from the experience gained both in the industry and in the research lab, on the following classical microwave frequency standards: active and passive H, conventional and laser pumped Cs beam tube, small conventional and laser pumped Rubidium. The accent is put on the Rubidium standard.

Busca, Giovanni↗
NASA NTRS1990

A highly stable crystal oscillator applied to geodetic VLBI experiment

Instead of a hydrogen maser, a carefully selected Crystal oscillator which is phase locked to a Cesium (Cs) frequency standard of a geodetic VLBI experiment. The domestic VLBI experiment with 55 km baseline using the Crystal oscillator at one end was made in Japan and the obtained error of the baseline vector components were 4 cm, and that of the baseline length was 3 cm. This system may be operated after only 2 hours warm up. These results coincides with those of conventional geodetic Laser ranging and VLBI using a hydrogen maser within the formal error. A VLBI experiment with over 1000 km baselines were carried out successfully from October 1988, and over 11000 km baseline between Japan and Antarctica was carried out successfully in January 1990.

Kiuchi, Hitoshi↗
NASA NTRS1990

Rubidium atomic frequency standards for GPS Block IIR

The Rubidium Atomic Frequency Standards (RAFS) were provided for the GPS Block IIR NAVSTAR satellites. These satellites will replenish and upgrade the space segment of the Global Positioning System in the mid 1990s. The GPS RAFS Rb clocks are the latest generation of the high-performance rubidium frequency standards. They offer an aging rate in the low pp 10(exp 14)/day range and a drift-corrected 1-day stability in the low pp 10(exp 14) range. The Block IIR version of these devices will have improved performance, higher reliability, smaller size, and greater radiation hardness. The GPS Block IIR atomic clocks have a natural frequency configuration whereby they output a frequency of about 13.4 MHz that is a submultiple of the atomic resonance of Rb (or Cs). The RAFS operates at a low, fixed C-field for increased stability. The GPS Block IIR RAFS design, including the changes and improvements made, and the test results obtained are described.

Riley, William J.↗
NASA NTRS1991

Overview of European and other non-US/USSR/Japan launch vehicle and propulsion technology programs

The following subject areas are covered: majority of propulsion technology development work is directly related to the ESA's Ariane 5 program and heavily involves SEP (Societe Europeenne de Propulsion) in all areas; Hermes; advanced work on magnetic bearings for turbomachinery; electric propulsion using Cs and Xe propellants done by SEP in France, MBB ERNO in West Germany, and by Culham Lab in UK; successfully tested fired H/O composite nozzle exit cone on 3rd stage of Ariane; turbine blades made of composites to allow increase in gas temperature and improvement in efficiency; combined cycle (turboramjet-rocket) engine analysis work done by Hyperspace; and ESA advanced program studies.

Rice, Eric E.↗