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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Determination of Van der Waals broadening at temperatures of astrophysical interest.

Discussion of the results of experiments analyzing the widths of shock-excited emission lines at temperatures of about 5000 K. The width of two neutral silicon lines (4102 and 5948 A) were measured as broadened by argon, and the shift of one of these lines (4102 A) was determined. Likewise, the width one of the lines of cesium (4593 A) was measured as broadened by argon and neon. These data are compared with other experimental data to determine the temperature dependence of the broadening. Significant disagreements with simple theory are found, the experimental values of the widths being larger than the theoretical values by factors of 1.5-2.

Evans, J. M., Jr.↗
NASA NTRS1972

Can astrophysical abundances be taken seriously.

The essential feature underlying abundance analysis is the assumption that local thermodynamic equilibrium prevails in a stellar atmosphere - i.e., that all relevant distribution functions, except that for the photons themselves, are thermal and determined by the local temperature. It is pointed out that the blanket assumption of local thermodynamic equilibrium in stellar atmospheres is a fundamental weakness. The assumption can only be valid if collisional processes are dominant in bringing about transitions between the excitation states of an atom. It has, however, been shown that the density in a stellar atmosphere is so low that, on the contrary, radiative processes are predominant.

Worrall, G.↗
NASA NTRS1970

Galactic astronomy; Proceedings of the Second Summer Institute for Astronomy and Astrophysics, State University of New York, Stony Brook, N.Y., June 19-July 17, 1968. Volumes 1 & 2.

Basic problems on the structure of our galaxy are presented. The essentially spiral structure of the galaxies is examined by a theory of the spiral shape, and by a study of the spiral structure with the 21-cm line of neutral hydrogen. Irregular spirals are discussed, and some problems that arise as a result of large deviations from the regular spiral structure are treated. The density wave theory of spiral structure is compared with the observed spiral structure of the galaxies. A section on the star migration technique, which is used to test the density wave theory of galactic spirals, is included. The interstellar medium is described in terms of such phenomena as supernova explosions and cosmic rays, both of which contribute to the energy balance of the medium. Other topics that are germaine to a description of the interstellar medium are the UV spectrum, kinematics of interstellar clouds, and ionization equilibrium. The implications of spiral galactic shock pattern on star formation along spiral arms are investigated, and by means of a blast wave model, it is shown that a hydrodynamic shock of galactic scale exists in galaxy M82.

Chiu, H.-Y.↗
NASA NTRS1972

RKR Franck-Condon factors for blue and ultraviolet transitions of some molecules of astrophysical interest and some comments on the interstellar abundance of CH, CH+ and SiH+.

RKR Franck-Condon factors for thirteen of the blue and ultraviolet transitions of AlF, AlO, BH, BD, CH, CD, CH(+), SiO and SiH(+) have been calculated. The interstellar abundances of CH, CH(+) and SiH(+) are discussed with regard to recent laboratory measurements, our Franck-Condon factors, and observations of the sun and the interstellar medium.

Liszt, H. S.↗
NASA NTRS1973

Smithsonian Astrophysical Observatory Reference System Bulletin, no. 1

The reference system is described which involves timing, scale, coordinate systems and their transformations, and observations of the rotation of the earth. Timing (epochs) and STADAT timing corrections are discussed. The coordinates for locations, and MSL height are listed for each observing station.

Source record↗
NASA NTRS1972

Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I.

A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.

Canuto, V.↗
NASA NTRS1972

Spectroscopy of tetrabenzporphin molecules and possible astrophysical implications.

Quasi-line spectra of MgTBP (chi) and H2TBP are presented with a view toward laboratory simulation of the diffuse interstellar spectra. Experimental results are discussed which strongly suggest that molecule chi meets all the critical tests for spectral identification. The IR spectrum and visible data of molecule chi are discussed and analysed in terms of a simple vibronic self-consistent energy level diagram.

Johnson, F. M.↗
NASA NTRS1973

Some magnetic null lines of astrophysical interest.

A line list is presented for magnetic null lines found in the Ultraviolet Multiplet Table and in selected spectral analyses for use in detailed studies of magnetic peculiar A star atmospheres.

Adelman, S. J.↗
NASA NTRS1973

Transition radiation in astrophysics.

Transition radiation produced by relativistic electrons traversing cosmic grains is investigated as a possible source of celestial X rays. The detailed theory of transition radiation including the formation-zone effect is used to calculate the X-ray emissivity in interstellar space. It is found that the largest contribution of transition radiation to the observed X-ray emission from the galactic disk is at about 2 keV, where less than about 0.3% of the observed emissivity is due to transition radiation. At higher energies transition radiation is strongly suppressed by the formation-zone effect, while at lower energies the observed emissivity increases much faster with decreasing energy than does transition radiation. Transition radiation is also compared with bremsstrahlung, synchrotron emission, and Compton scattering. The comparison with synchrotron emission and bremsstrahlung relates X-ray production by transition radiation to radio emission and to approximately 100-MeV gamma-ray production, respectively.

Yodh, G. B.↗
NASA NTRS1973

Evaluation of astrophysical hypotheses.

The aim of this article is to set out a bookkeeping procedure for formalizing the process of assessing a hypothesis by comparison of conclusions drawn theoretically from this hypothesis with facts obtained by reduction of observational data. The formalism used is that of probability theory. A key role is played by Bayes's rule representing the inductive process of adjusting a degree of belief in response to new information. Formulae are derived which show (1) how the probability of each hypothesis should be adjusted in response to information concerning one item, and (2) how such estimates concerning more than one item may be combined. The procedure is illustrated by a work sheet showing how a few facts and conclusions concerning pulsars were combined to appraise the neutron-star and white-dwarf hypotheses.

Sturrock, P. A.↗
NASA NTRS1974

Research on infrared astrophysics and X ray and XUV astronomy

The infrared research was divided into two related subjects, observations at wavelengths less than 34 microns and millimeter wavelength observations. A new complex of infrared sources in the Orion Nebula observed along with a broad range of galactic and extragalactic objects. The Comet Kohoutek was measured in the 1-20 micron wavelength region and its thermal properties agreed closely with those of Comet Ikeya-Seki. Combined infrared and photoelectric studies of the Makarian galaxies showed them to have a composite spectrum with a large emission feature in the far infrared. The development of one millimeter photometry and composited bolometers is described. A technique of reconstructing two dimensional surface brightness distributions with appropriate errors from individual strip scans was developed. Model parameters were determined by fitting data in non-linear systems. Results show spectral parameter uncertainties are underestimated or incorrectly evaluated in most studies.

Source record↗
NASA NTRS1974

Cross section calculations of astrophysical interest

Cross sections are discussed for rotational excitation associated with theories of absorption and emission lines from molecules in space with emphasis on H2CO, CO, and OH by collisions with neutral particles such H, H2, and He. The sensitivity of the Thaddeus equation for the H2CO calculation is examined.

Gerjuoy, E.↗
NASA NTRS1974

Gamma ray astrophysics

Gamma ray production processes are reviewed, including Compton scattering, synchrotron radiation, bremsstrahlung interactions, meson decay, nucleon-antinucleon annihilations, and pion production. Gamma ray absorption mechanisms through interactions with radiation and with matter are discussed, along with redshifts and gamma ray fluxes.

Stecker, F. W.↗