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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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NASA NTRS1984

The nature of the filaments northeast of the supernova remnant IC 443

New optical spectrophotometry of the faint filaments northeast of the bright supernova remnant IC 443 show emission-line ratios very similar to those seen in the bright filaments of IC 443 and other supernova remnants. This suggests that these northeastern filaments also represent shock-heated interstellar gas and are not simply the southern boundary of the neighboring H II region S249 as previously suspected. If these filaments are associated with IC 443, they then reveal a much more extended remnant structure than previously assumed and permit a relatively accurate determination of IC 443's distance via its interaction with S249.

Fesen, R. A.↗
NASA NTRS1984

A new dimension in space experimentation

Based on the Space Shuttle's ability to place the Long Duration Exposure Facility (LDEF) in space and later retrieve it, a new opportunity for scientific exploration in space is studied. The LDEF which is scheduled to be placed in orbit in 1984 and returned to earth after one year in space is described. It is a large unmanned facility 9 m in length and 4 m in diameter and flying at an 482 km orbit. It is pointed out that the LDEF allows investigators to have their experiments returned to them for in-depth analysis, eliminates the need for complex systems to transmit data to earth, does not require propulsion equipment, and increases the kinds of experiments that can be performed. A description is given for each of the five categories of the experiments provided by the LDEF: (1) evaluation of the impact of space environments on materials used for thermal coatings on polymer-matrix composites, on optics, and on quartz-crystal oscillators; (2) experiments with unique heat pipe systems having the goal to achieve temperature control of + or - 6 F; (3) evaluation of solar array materials; (4) growth of single crystals of lead sulfite, calcium carbonate, and synthetic metals; and (5) scientific experiments to determine the chemistry of micrometeoroids and to identify isotopes in interstellar gas and ultra-heavy cosmic ray nuclei. Finally, the project SEEDS (Space Exposed Experiment Developed for Students) which experiments with tomato seeds behavior in zero gravity is discussed.

Sandy, M. L.↗
NASA NTRS1984

Measurements of transition probabilities for spin-changing lines of atomic ions used in diagnostics of astrophysical plasmas

The intensities of ultraviolet, spin-changing, 'intersystem' lines of low-Z atomic ions are frequently used in determinations of electron densities and temperatures in astrophysical plasmas as well as in measurements of element abundances in the interstellar gas. The transition probabilities (A-values) of these lines, which are about five orders of magnitude weaker than allowed lines, have not been measured heretofore and various calculations produce A-values for these lines that differ by as much as 50 percent A radio-frequency ion trap has been used for the first measurements of transition probabilities for intersystem lines seen in astronomical spectra. The measurement procedure is discussed and results for Si III, O III, N II, and C III are reviewed and compared to calculated values. Discrepancies exist; these indicate that some of the calculated A-values may be less reliable than has been beleived and that revisions to the electron densities determined for some astrophysical plasmas may be required.

Smith, P. L.↗
NASA NTRS1985

Diffuse galactic annihilation radiation from supernova nucleosynthesis

The propagation of MeV positrons in the outer ejecta of type I supernovae was investigated. It was found that the positrons created at times of approx 100 days propagated along magnetic field lines in the outer ejecta without any appreciable pitch-angle scattering or excitation of hydromagnetic waves. The lack of significant pitch-angle scattering is well consistent with models of wave excitation and scattering by resonant interactions. This occurs because time periods to scatter the particles or to excite waves are significantly longer than escape times. Thus it is expected that, when positrons are not coupled to the ejecta by Coulomb collisions, they escape from the relatively cold, dense ejecta and reside predominantly in the tenuous, hotter, shock-heated interstellar gas. In the tenuous shock-heated gas the positron lifetime against annihilation is much greater than lifetimes in the dense ejectra. Thus the production of steady-state diffuse annihilation radiation by some fraction of these escaped positrons seems probable.

Higdon, J. C.↗
NASA NTRS1985

The role of cosmic rays in magnetic hydrodynamics of interstellar medium

Cosmic ray (CR) propagation in the Galaxy and generally in the cosmic plasma is usually considered in the diffusion approximation. The diffusion is regarded to result from CR scattering due to their interaction with a magnetic and an electric field. In most cases the fields are assumed to be given. Meanwhile, in the Galaxy the CR energy density w sub cr is similar to I eV/cm, i.e., it is comparable with the energy densities of the magnetic field and turbulent motions in the interstellar gas. Therefore, for the Galaxy it becomes necessary to take into account the influence of CR on the gas dynamics and on the magnetic fields in this gas. The simplest way to this is to use the hydrodynamic approximation, but this is possible only on scales greatly exceeding the CR free path lambda before scattering and only for times larger than lambda/v approx. equals lambda/c. One should thus obtain corresponding MHD equations and establish the limits of their applicability.

Ginzburg, V. L.↗
NASA NTRS1985

Measurements of Fe and Ar fragmentation cross sections

Measurements are reported of the yields of individual isotopes of Cr to Co(Z = 24 to 27) resulting from the fragmentation of Fe-56, and the isotopes of Mg to K(Z = 12 to 19) resulting from the fragmentation of Ar-40. Recent advances in the resolution and collecting power of cosmic ray instrumentation, have led to dramatic improvements in the precision of cosmic ray composition measurements, both elemental and isotopic. The interpretation of these measurements is presently limited by uncertainties in the fragmentation cross-sections needed to correct for nuclear interactions with the interstellar gas. Cosmic ray propagation codes now rely mainly on semi-empirical cross-section formulae developed by Silberberg and Tsao (S&T), which have a typical uncertainty of approximately 25%. Relative isotope yields from the fragmentation of approximately 380 MeV/nucleon Fe-56 e and approximately 210 MeV/nucleon Ar-40 r in CH2 targets, observed during the calibration of two cosmic ray spectrometers at the Lawrence Berkeley Laboratory Bevalac are reported. These are compared with calculated yeilds based on the S&T cross-section formulae.

Lau, K. H.↗
NASA NTRS1984

On interstellar Fe X forbidden line absorption toward Cepheus OB2

A weak interstellar absorption line which can be identified as the forbidden line of Fe X 6375 A is observed in the spectrum of the A2 Ia star Nu Cep, which is a member of the Cepheus OB2 association. The equivalent width, width, and radial velocity of the line differ indistinguishably from those of similar absorption previously detected uniquely toward the O6f star Lambda Cep, another association member located at a projected distance of about 50 pc from Nu Cep. The absorption may reveal a particularly dense, low-latitude concentration of hot, foreground interstellar gas of the kind generally responsible for the observed soft X-ray background.

Hobbs, L. M.↗
NASA NTRS1984

The abundance of interstellar lithium

The interstellar Li I 6707-A absorption line is detected toward Rho Oph A at an equivalent width of 3.1 + or - 1.9 (3 sigma)mA. Upper limits near 1 mA also are found toward seven other stars, including 55 Cyg, toward which relatively strong Li I absorption was previously reported. The four positive detections and the eight upper limits now available for the 6707-A line indicate that Li is not significantly depleted from the interstellar gas.

Hobbs, L. M.↗
NASA NTRS1985

NGC 2110 - A Seyfert and X-ray elliptical galaxy with displaced kinematic and light centers

Kinematic and imaging observations of NGC 2110 are reported and it is found that the interstellar gas is orbiting with projected rotation axis parallel to the minor axis of the stellar light. The rotation curve is steep close to the center and flat farther out. However, the nucleus is displaced by about 220 pc from the apparent mass center of the galaxy. This last result is discussed in terms of models invoking differential obscuration of stars and gas, non-Keplerian motion of the gas, or a large mass of unseen material which dominates the rotation curve.

Wilson, A. S.↗
NASA NTRS1985

Interstellar H3(+) - Possible detection of the 1(10)-1(11) transition of H2D

An interstellar line has been detected in emission at the expected submillimeter wavelength of the 1(10)-1(11) transition of H2D(+), the deuterated verison of the primary ion (H3/+/) in the favored ion-molecule reaction scheme for interstellar gas phase chemistry. The strength of the line is in approximate agreement with the theoretically anticipated H2D(+) abundance.

Phillips, T. G.↗
NASA NTRS1985

Combined ultraviolet studies of astronomical source

As part of its Ultraviolet Studies of Astronomical Sources the Smithsonian Astrophysical Observatory for the period 1 Feb. 1985 to 31 July 1985 observed the following: the Cygnus Loop; oxygen-rich supernova remnants in 1E0102-72; the Large Magellanic Cloud supernova remnants; P Cygni profiles in dwarf novae; soft X-ray photoionization of interstellar gas; spectral variations in AM Her stars; the mass of Feige 24; atmospheric inhomogeneities in Lambda Andromedae and FF Aquarii; photometric and spectroscopic observation of Capella; Alpha Orionis; metal deficient giant stars; M 67 giants; high-velocity winds from giant stars; accretion disk parameters in cataclysmic variables; chromospheric emission of late-type dwarfs in visual binaries; chromospheres and transient regions of stars in the Ursa Major group; and low-metallicity blue galaxies.

Dupress, A. K.↗
NASA NTRS1985

All-aluminum optical system for a large cryogenically cooled far infrared echelle spectrometer

In the past few years, NASA's Kuiper Airborne Observatory (KAO) has made it possible to conduct pioneering observations of far infrared lines from astronomical sources. Such observations, in the case of wavelengths in the approximate range from 20 to 350 microns, cannot be performed from ground-based sites, because of telluric water absorption effects. Lines in the considered range provide information about the interstellar gas in molecular, neutral atomic, and ionized form of occurrence. The present paper provides a description of the development of the cryogenic optical system of a spectrometer designed to exploit the potential of the KAO for observing the far infrared lines. Attention is given to design goals and considerations, details of optical design, the fabrication of the optical system, the cryostat, and performance.

Erickson, E. F.↗
NASA NTRS1986

The radial distribution of galactic gamma rays. III - The distribution of cosmic rays in the Galaxy and the CO-H2 calibration

The cosmic ray (CR) distribution in the Galaxy inside the solar circle is determined by using the kinematics of both H I and CO to ascertain the spatial distribution of the interstellar gas. The conversion factor between integrated CO line intensity and the molecular hydrogen column density is found, and possible large-scale variations of this relationship throughout the Galaxy are investigated. The galactocentric CR distributions are shown to be described satisfactorily by exponential distributions for radii larger than about three, with a radial scale length of 4-11 kpc for electrons and a scale length greater than 18 kpc for nuclei.

Bloemen, J. B. G. M.↗
NASA NTRS1985

Massive black holes in galactic halos?

In the present attempt to resolve the problems posed by the composition of dark halos and the heating of stellar disks, under the assumption that galaxy halos are composed of massive black holes, it is noted that the black holes must have masses of the order of one million solar masses. The heating mechanism proposed yields predictions for the dependence of the velocity dispersion on time, and for the shape of the velocity ellipsoid, which are in good agreement with observations. Attention is given to the constraints set by dynamical friction causing black holes to spiral to the Galactic center, by the possible presence of dark matter in dwarf spheroidal galaxies, and by the accretion of interstellar gas by the black holes that produce luminous objects in the Galaxy.

Lacey, C. G.↗
NASA NTRS1986

Local interstellar gasdynamical stability in spiral arm flow

The stability of two-dimensional interstellar gas flow passing through a spiral potential has been investigated. The background flow is assumed to move in a tightly wound potential, which may be regarded as external or self-generated. The unperturbed flow, which may be time dependent, is self-gravitating and satisfies the Roberts equations of motion. A polytropic, single-fluid assumption has been used. Magnetic effects are not considered. The motivation behind this work is to try to understand how much of the diversity of spiral arm morphology can be understood by large scale gas dynamical processes alone. To this end, it is suggested that spurring and feathering, and forming molecular cloud complexes may be closely related in the sense of having dynamically similar origins.

Balbus, S. A.↗
NASA NTRS1987

Efficient star formation in the bright bar of M83

The bright molecular bar in M83 was detected standing out as a 100% enhancement of molecular emission with respect to the off-bar emission at the same radii. The spatial variations in the star formation efficiency, as traced by H alpha emission and the surface density of the interstellar gas, in M83 and M51 were compared. Both the central bar of M83 and the spiral arms of M51 are regions characterized by high massive star formation rates. For M83, it is ascribed that both the gas surface density and the star formation efficiency are high to the hydrodynamics of the central region.

Lord, S. D.↗
NASA NTRS1986

Cometary memory of interstellar aluminum

It is shown that the distribution of refractory metals in a comet-nucleus drill core carries a chemical memory quite distinct from that of volatiles. Using aluminum as an example, it is demonstrated that very refractory structures, either grain cores or refractory aggregates of cores, must be much older than the volatile component. It is argued that isotopic anomalies are specifically associated with aluminum. An evolutionary model capable of rationalizing the interstellar gas depletions of Al and Mg is advocated. The distribution of Al in comets is shown to be crucial to understanding the origin of comets and of the solar system.

Clayton, Donald D.↗
NASA NTRS1986

The interstellar carbon abundance. II - Rho Ophiuchi and Beta Scorpii

A procedure designed to obtain increased sensitivity from high-dispersion IUE spectra by using a flat-field spectrum to remove nonrandom noise due to the response pattern of the SEC vidicon detector is described. Application of this procedure to spectra of Rho Oph and Beta(1) Sco near the spin-forbidden interstellar 2325 line of C II yields 2 sigma upper limits on absorption of W (lambda) not greater than about 4 mA. The resulting depletion of carbon from the interstellar gas toward Rho Oph exceeds a factor of 1.4.

Welty, D. E.↗