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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 1,621 records · Page 90
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NASA NTRS1987

Maps of millimeter wave emission from three galactic star-forming regions

In order to investigate the gas dynamics around young stellar objects, three sources were mapped which exhibit supersonic velocities in the 115 GHZ, J = 1-0 transition of CO. The maps, made with the Owens Valley Radio Observatory Millimeter Interferometer, are the highest spatial resolution images currently available of millimeter-wave continuum and line emission from the sources S106, S87, and LkHalpha101. Observations were made in the CS (J = 2-1) and C-13O (J = 1-0) transitions. In all the sources, the observations indicate that the ionized stellar wind is sweeping up ambient molecular gas. The molecular gas is found adjacent to the outer edges of the ionized winds, which originate in embedded infrared sources. From the observations presented, it may be inferred that the outflowing ionized winds are channeled by the surrounding dense, neutral gas.

Barsony, Mary↗
NASA NTRS1987

Star formation and dynamics in starburst nuclei

A simple model is presented for gas inflow through a disk galaxy driven by interacting galaxies through the action of a non-axisymmetric disturbance acting on the disk whose gas is modelled as an ensemble of gas clouds. Cloud collisions, as well as being a vital process in forcing gas inflow to the center of the disk, are also assumed to generate massive stars. This ever increasing rate of gas flow toward the center of the galaxy and the associated rapid increase in cloud collisions lead to a centrally concentrated starburst. Starbursts have important consequences for the immediate environment of galaxies. Mildly collimated outflows can be driven by a combination of multiple supernovae and OB star winds. Jets associated with activity in the galactic nucleus can interact strongly with a starburst environment.

Norman, Colin A.↗
NASA NTRS1987

Starburst-driven superwinds from infrared galaxies

New data is presented that indicate that strong far infrared galaxies commonly have largescale emission line nebulae whose properties are suggestive of mass outflows (superwinds), presumably driven by the high supernova rate associated with the central starburst. These data include longslit spectra of M82 which show that the radial variation of the gas pressure in the emission line nebula is in excellent agreement with a previous wind model. The M82 nebula also has a LINER spectrum, consistent with shock heating. Morphologically and spectroscopically similar emission line nebulae were found in NGC253, and Arp 220 and NGC6240. A longslit spectroscopic investigation was conducted of 20 additional very powerful far-infrared galaxies and found that they generally have spatially extended emission line nebulae whose spectra closely resemble that of the M82 nebula. If the superwind interpretation is correct, it could have many important consequences in extragalactic astronomy.

Heckman, Timothy M.↗
NASA NTRS1986

The physics of the cometary contact surface

The contact surface, which separates outflowing cometary plasma from solar wind controlled cometary plasma, is explained in terms of a balance between the magnetic pressure gradient force and ion-neutral drag. Giotto data indicate that the plasma pressure inside the contact surface cannot balance the sum of the external plasma and magnetic pressures, and therefore a Venus-like ionopause is not present at the contact surface. An expression for the magnetic field strength as a function of cometocentric distance is derived from the momentum equation. The theoretical magnetic field profile agrees quite well with the profile measured by the Giotto magnetometer in the vicinity of the contact surface.

Cravens, Thomas E.↗
NASA NTRS1986

Velocity-resolved observations of water in Comet Halley

An infrared spectrum of comet Halley was recorded at the Kuiper Airborne Observatory with an instrumental velocity resolution of 1.1 km/sec. A total of 13 emission lines in the 2.65 micron spectral region were assigned to neutral gaseous H2O : 10 in the 001 to 000 band and 3 in the hot 011 to 010 band. The position and widths of these lines are functions of the gas velocity field in the coma. Analysis indicates that the neutral gas outflow is widely dispersed about the nucleus. This spectroscopic picture is consistent with spacecraft images that show multiple jets releasing material into most of the sunfacing hemisphere.

Larson, Harold P.↗
NASA NTRS1986

The atomic carbon distribution in the coma of Comet Halley

The radial distribution of CO, OI, Ci, and CII emissions in the coma of comet Halley were measured by a long-slit far ultraviolet spectrograph aboard a sounding rocket on 26 Feb. and 13 Mar. 1986. While the CO profiles strongly suggest that CO is vaporized directly from the nucleus, the observed carbon distribution is not consistent with a radial outflow model of CO, suggesting an additional source of atomic carbon in the inner coma. Based on the in situ plasma measurements from the Vega and Giotto spacecraft, it is possible that this additional source of carbon could be the recombination of ionized CO in the inner coma.

Woods, T. N.↗
NASA NTRS1986

HCN production from Comet Halley

Observations of the HCN J=1-0 rotational transition at 3.4 mm wavelength in comet P/Halley with a 14m antenna were obtained during 56 individual observing sessions between Nov. 1985 and May 1986. The HCN production rate is well correlated with the total visual magnitude of the comet, indicating that HCN follows the overall gas and dust production. However, comparison of HCN production to the total gas production of the comet indicates that it is a relatively minor consitiuent with 0.1% of the abundance of H2O. Spectra obtained by binning the HCN data with heliocentric distance show that the HCN line width, and thus the parent outflow velocity, increases with decreasing heliocentric distance, and that there is a tendency for the lines to be blue shifted as expected from the observed anisotropic outgassing from the nucleus. There is evidence of day-to-day time variability in the total HCN emission and variations in the HCN hyperfine ratios from their LTE values.

Schloerb, F. Peter↗
NASA NTRS1987

Design and demonstrate the performance of cryogenic components representative of space vehicles: Start basket liquid acquisition device performance analysis

The objective was to design, fabricate and test an integrated cryogenic test article incorporating both fluid and thermal propellant management subsystems. A 2.2 m (87 in) diameter aluminum test tank was outfitted with multilayer insulation, helium purge system, low-conductive tank supports, thermodynamic vent system, liquid acquisition device and immersed outflow pump. Tests and analysis performed on the start basket liquid acquisition device and studies of the liquid retention characteristics of fine mesh screens are discussed.

Source record↗
NASA NTRS1986

Numerical solutions of the complete Navier-Stokes equations

Using ideas from the kinetic theory, the Navier-Stokes equations are modified in such a way that they can be cast as a set of first order hyperbolic equations. This is achieved by incorporating time dependent terms into the definition of the stress tensor and the heat flux vectors. The boundary conditions are then determined from the theory of characteristics. Because the resulting equations reduce to the traditional Navier-Stokes equations when the steady state is reached, the present approach provides a straightforward scheme for the determination of inflow and outflow boundary conditions. The method is validated by comparing its predictions with known exact solutions of the steady Navier-Stokes equations.

Hassan, H. A.↗
NASA NTRS1985

High spectral resolution Fabry-Perot interferometer measurements of Comet Halley at H-alpha and 6300 A

A 40.6-cm Newtonian telescope was interfaced to the Fabry-Perot interferometer at the Arecibo Observatory to make high-spectral-resolution measurements of Comet Halley emissions at 6562.72 A (H-alpha) and 6300.3 A (O I). The atomic hydrogen outflow velocity was found to be approximately 7.9 + or - 1.0 km/s. In general, the H-alpha spectra are highly structured, and indicative of a multiple component atomic hydrogen velocity distribution. For O (1D), implied production rates of 6.44 + or - 3.0 x 10 to the 28th/s and 5.66 + or - 2.7 x 10 to the 28th/s were found on March 15 and 17, respectively.

Kerr, R. B.↗
NASA NTRS1986

The role of dust in mass loss from late-type stars

It is noted that, in almost all late-type stars with measured mass loss rates, there is sufficient momentum in the radiation to dominate the dynamics. The opacity of the material is sufficiently great to render radiation pressure important; the dust forms close enough to the central star for radiation pressure to account for the observed outflow velocities. Pulsations appear to be important in raising the material far enough above the photosphere for grains to condense.

Jura, M.↗
NASA NTRS1986

Gamma-ray bursters at cosmological distances

It is proposed that some, perhaps most, gamma-ray bursters are at cosmological distances, like quasars, with a redshift of about 1 or 2. This proposition requires a release of supernova-like energy of about 10 to the 51st ergs within less than 1 s, making gamma-ray bursters the brightest objects known in the universe, many orders of magnitude brighter than any quasars. This power must drive a highly relativistic outflow of electron-positron plasma and radiation from the source. It is proposed that three gamma-ray bursts, all with identical spectra, detected from B1900 + 14 by Mazets, Golenetskii, and Gur'yan and reported in 1979, were all due to a single event multiply imaged by a gravitational lens. The time intervals between the successive bursts, 10 hr to 3 days, were due to differences in the light travel time for different images.

Paczynski, B.↗
NASA NTRS1986

Infrared spectra of rotating protostars

Earlier calculations of the infrared emission expected from stars in the process of being made are corrected to include the most important observable effects of rotation and generalized. An improved version of the spherical model of a previous paper is developed, and the corresponding emergent spectral energy distributions are calculated for the theoretically expected mass infall rate in the cores of cool and quiescent molecular clouds. The dust grain opacity model and the temperature profile parameterization are improved. It is shown that the infrared spectrum of the IRAS source 04264+2426, which is associated with a Herbig-Haro object, can be adequately represented in terms of a rotating and accreting protostar. This strengthens the suggestion that collimated outflows in young stellar objects originate when a stellar wind tries to emerge and reverse the swirling pattern of infall which gave birth to the central star.

Adams, F. C.↗
NASA NTRS1986

Field-aligned plasma flow in MHD simulations of magnetotail reconnection and the formation of boundary layers

The outflow from a reconnection region in a realistic magnetotail geometry is studied using a two-dimensional time-dependent, compressible, resistive MHD code. Two cases are emphasized: (1) the evolution of near-earth reconnection, which grows in the form of an internal unstable mode after gradual externally forced changes have initiated an anomalous dissipation process, and (2) the evolution of more distant reconnection under influence of a nonuniform inflow that forces reconnection to occur at a given location in the distant tail. In both cases, it is demonstrated that plasma flow is primarily parallel to the magnetic field in regions away from the localized area of reconnection and outside a narrow central layer.

Birn, J.↗
NASA NTRS1986

Velocity-resolved observations of water in comet Halley

High-resolution observations of H2O in comet Halley are presented. The positions and widths of the H2O emission line profiles are indicative of the coma's velocity field characteristics. Spectral line shape changes are used to infer temporal variations in the kinematic properties of the outflow. The results suggest that H2O is released into the coma by way of multiple jets.

Larson, Harold P.↗
NASA NTRS1986

HCN production from comet Halley

The HCN J = 1-0 rotational transition at 3.4 mm wavelength has been detected and has been monitored in comet P/Halley during a total of 56 individual observing sessions between November 18, 1985 and May 11, 1986. The HCN spectra show significant daily variations in total intensity, but the average HCN production rate is well correlated with the visual magnitude of the comet over the range of heliocentric distance observed (between 0.59 and 1.8). Observations of the ratios of the F = 2-1 and F = 1-1 hyperfine components also exhibit significant daily variations but are, in the mean, consistent with the 5:3 ratio expected from the statistical weights of the hyperfine levels. The outflow velocity of the coma, deduced from the HCN linewidths, is 0.87 + or - 0.12 km/s, which is consistent with recent theoretical estimates as well as the measurements of the Giotto spacecraft.

Schloerb, F. Peter↗
NASA NTRS1987

Computational aeroacoustics of propeller noise in the near and far field

Techniques for applying the NASPROP-E computer code (Bober et al., 1983) to characterize the acoustic field of a transonic propfan are described and demonstrated for the case of the SR-3 propfan. It is pointed out that NASPROP E accounts for the nonlinear quadrupole, monopole, and dipole noise sources. The approach used, based on that of White (1984) and Korkan et al. (1985 and 1986), is described in detail, and the results of simulations employing different (reflective and nonreflective) inflow-outflow boundary conditions and azimuthal mesh spacings are presented in graphs and briefly discussed.

Forsyth, D. W.↗
NASA NTRS1986

Mass fractionation during transonic escape and implications for loss of water from Mars and Venus

Hydrodynamic escape of hydrogen from a planetary atmosphere can remove heavier gases as well as hydrogen, provided that the escape rate is sufficiently large. Analytic approximations for the degree of mass fractionation of a trace species during hydrodynamic escape are compared with accurate numerical solutions for the case of transonic outflow. The analytic approximations are most accurate when the ratio of molecular weights of the heavier and lighter constituents is large so that nonlinear terms in the momentum equation for the heavy constituent become small. The simplest analytic formula is readily generalized to the case where a heavy constituent is also a major species. Application of the generalized formula to hypothetical episodes of hydrodynamic escape from Venus and Mars suggests that both hydrogen and oxygen could have escaped; thus, substantial quantities of water may have been lost without the need to oxidize large amounts of the crust.

Zahnle, Kevin J.↗