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NASA NTRS1982

Hydrogen two photon emission in the UV spectrum of type 2 supernovae

The continuum emission of Type 2 supernovae demonstrates an ultraviolet (UV) excess when fit by black body emission is attempted. The H two photon emission is advanced as an explanation of the UV excess. A function by which the UV spectra of two Type 2 supernovae (SN 1979c in NGC 4321 and SN 1980k in NGC 6946) are fitted with U,B,V photometric data is presented. The angular velocity of expansion of the supernovae envelope is derived. From this, the linear velocity of expansion and the distances of the parent galaxies are derived. A distance of 17.3 Mpc is obtained for NGC 4321, and a distance of 7.1 Mpc for NGC 6946.

Benvenuti, P.↗

NASA NTRS1982

Aerosound from corner flow and flap flow

Noise generation at the edge of a wing flap is analyzed. The phenomenon as a single vortex moving around a corner in an incompressible, potential flow is modelled. Vortex image retarding effects are proposed as an explanation for small Strouhal numbers. The model surface pressures, sound pressures (using Curle's theory), and Mach number dependencies agree with wind tunnel experiments. A double pressure peak is found in the model (credited to image action) which is qualitatively similar to measured sound correlations. Incompressible flow aerosound calculations are discussed. The effects of a series of vortices moving in the same idealized potential flow are also studied. The vortices are assumed to be statistically independent so their intensities can be added. The frequency of appearance of the vortices are determined from measurements. Diffraction effects caused by the presence of the wing near the dipole sound radiators on the flap surfaces are included.

Meecham, W. C.↗

NASA NTRS1982

Changes in interstellar atomic abundances from the galactic plane to the halo

A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron.

Jenkins, E. B.↗

NASA NTRS1982

Identification of the emission features near 3.5 microns in the pre main sequence star HD 97048

The spectrum of HD97048 was measured with a resolving power of 450 between 3.37 and 3.64 microns. The prominent feature near 3.5 microns is well resolved, with a peak at 3.53 microns and a wing extending to a shorter wavelength. The weaker feature near 3.4 microns is found to peak at 3.43 microns, in contrast to the 3.40 micron feature seen in other astronomical objects. The observed spectrum strongly resembles laboratory spectra of mixtures of monomeric and dimeric formaldehyde embedded in low temperature solids. Of various possible excitation mechanisms, ultraviolet pumped infrared fluorescence of formaldehyde in interstellar grains provides the best explanation for the observed spectrum of HD 97048.

Baas, F.↗

NASA NTRS1982

A theory of the Io phase asymmetry of the Jovian decametric radiation

An explanation of an asymmetry in the occurrence probability of the Io-dependent Jovian decametric radiation is proposed. Io generates stronger Alfven waves toward the south when it is in the northern part of the torus. This wave then generates decametric radiation in the northern ionosphere after it reflects in the southern ionosphere. The asymmetry then results from computing the propagation time of the alfven wave along this trajectory. The ray paths of the decameter radiation are calculated using a three dimensional ray tracing program in the Jovian ionosphere. Variations in the expected probability plots are computer for two models of the Jovian ionosphere and global magnetic field, as well as for several choices of the ratio of the radiated frequency to the X-mode cutoff frequency.

Hashimoto, K.↗

NASA NTRS1981

Observations of the magnetic field and plasma flow in Jupiter's magnetosheath

A comprehensive description is given of the Jovian MS magnetic fields, and explanations of these phenomena are proposed. While emphasizing Voyager 1 and 2 magnetic field observations and their relations to the plasma observations, it is also shown that the same phenomena are present in the Pioneer 10 magnetic field data. An unusually high occurrence of nearly north or south fields is observed in the outbound MS, especially in the vicinity of the MP. It is noted that the outbound MS fields and their variations tend to occur in a plane parallel to the local MP, according to large scale MP models.

Lepping, R. P.↗

NASA NTRS1981

Modeling the Jovian current sheet and inner magnetosphere

Voyager 1 and 2 magnetic field observations confirm and extend the earlier Pioneer 10 detection of the Jovian magnetodisc, a region of enhanced charged particles and plasma and reduced magnetic field intensity located near the magnetic equatorial plane. Modeling of the azimuthal current sheet by a finite thickness annulus of inner radius 5 Jovian radii, 5-Jovian radii thickness, and extending to about 50 Jovian radii provides detailed fits of the vector magnetic field perturbations observed in relation to the planetary field for distances less than 30 Jovian radii. Field line geometry is also investigated, and better insight into the phenomena of charged particle absorption by the Galilean satellites is obtained which provides improved explanations of observed effects due to Ganymede.

Connerney, J. E. P.↗

NASA NTRS1981

Daily and seasonal Viking observations of Martian bore wave systems

A Martian atmospheric phenomenon called a bore wave has been observed by the Viking imaging system during late spring and early summer of two Martian years, in the Tharsis Ridge region of the planet. The observational data are presented, and a tentative explanation is offered for the occurrence of this feature, formed by airflow and which behaves like a thermally induced diurnal katabatic breeze.

Hunt, G. E.↗

NASA NTRS1981

Rings in the solar system

The structure and composition of the rings of Jupiter, Saturn, and Uranus are discussed, with special attention given to the rings of Saturn. Processes that are known to shape the rings are then described. Alternative explanations for the origin of the rings are proposed. It is pointed out that the architecture of a ring system results from the interplay of a number of forces, among them gravitational forces due to moons outside the rings and the moonlets embedded in them, electromagnetic forces due to the planet's rotating magnetic field, and even the gentle forces exerted by the dilute gaseous medium in which the rings rotate.

Pollack, J. B.↗

NASA NTRS1981

Fragmentation in a rotating protostar - A re-examination of comparison calculations

The self-gravitating collapse of a rotating, isothermal protostellar cloud has been recalculated with two independent fluid-dynamic computer codes, in three space dimensions, with improved spatial resolution compared to previous calculations. The results again predict fragmentation and formation of a binary protostellar system with properties similar to those obtained in the lower-resolution calculations. The results, however, are in disagreement with those obtained with a particle-dynamic code by Gingold and Monaghan (1981) for the collapse of a cloud from the same initial conditions. Possible explanations for the divergent results are discussed.

Bodenheimer, P.↗

NASA NTRS1981

Charged dust in the outer planetary magnetospheres. III - Satellite impact geometries

Interplanetary dust grains entering the Jovian plasmasphere become charged, and those in a certain size range get magneto-gravitationally trapped in the corotating plasmasphere. The trajectories of such dust grains intersect the orbits of one or more of the Galilean satellites. Orbital calculations of micron sized dust grains show that they impact the outermost satellite Callisto predominantly on its leading face, while they impact the inner three - Io, Europa and Ganymede - predominantly on the trailing face. These results are offered as an explanation of the observed brightness asymmetry between the leading and trailing faces of the outer three Galilean satellites. The albedo of Io is likely to be determined by its volcanism.

Hill, J. R.↗

NASA NTRS1981

54 Cam - A new variable star

Differential photometry of the RS CVn-type binary 54 Cam is presented, which shows that the light was variable with a period of 10.163 + or - 0.009 d, and with an amplitude increase from 0.03 to 0.06 m between 1979 and 1980. The photometric period of 10.163 d is 9% shorter than the orbital period of 11.0764 d, and is suggested as an explanation for the radio emission from 54 Cam due to a process of connection, disruption, and reconnection of magnetic field lines.

Hall, D. S.↗

NASA NTRS1981

Anomalous resistivity on auroral field lines

Consideration is given to a possible explanation for the one-dimensional anomalous resistivity and breakdown of runaway acceleration observed in the auroral zones. It is shown that under conditions existing along auroral field lines, where the cyclotron frequency is greater than the plasma frequency and density fluctuations exceed 0.25, trapping of a major portion of the electron distribution function by large-amplitude ion cyclotron waves can inhibit the free acceleration of runaways and act to violate the conservation of the first adiabatic invariant for electrons above a certain threshold velocity. Particle simulations combining the effects of finite ion cavities and pitch angle scattering at the anomalous Doppler resonance are then presented which demonstrate the formation of a runaway distribution upon the application of a constant dc field and the effects of the instability at the anomalous Doppler resonance in preventing it. The necessity for further large-scale macrophysics simulations to gain a fuller understanding of the total system dynamics is pointed out.

Rowland, H. L.↗

NASA NTRS1981

Vestibular and oculomotor physiology; Proceedings of the International Meeting, New York, NY, September 22-25, 1980

Papers are presented showing recent progress in the understanding of the processing of visual and vestibular signals by the central nervous system to produce eye movements and postural responses. Specific topics include the directional sensitivity of hair cells to hair bundle deflection, the effects of gravity on rotatory nystagmus, the reticulovestibular organization associated with horizontal fast eye movement, the pathways controlling the extraocular eye muscles, the organization of visual-vestibular interaction in vestibular neurons, motion sickness due to vision reversal in stroboscopic light, and vestibular habituation during sinusoidal rotation. Attention is also given to vestibulo-ocular, vestibulocollic and cervicocollic reflexes, visual mossy fiber inputs to the flocculus, directional plasticity of the vestibulo-ocular reflex, the relation of active head rotation with eye-head coordination, instability in the optokinetic-vestibular system as an explanation for periodic alternating nystagmus, the effects of visual and nonvisual fixation on vestibular nystagmus, interaction of saccades with the vestibulo-ocular reflex, and the role of the plantar mechanoreceptor in equilibrium control.

Cohen, B.↗

NASA NTRS1981

Voltage gradients in solar array cavities as possible breakdown sites in spacecraft-charging-induced discharges

A possible explanation for environmentally-induced discharges on geosynchronous satellites exists in the electric fields formed in the cavities between solar cells - the small gaps formed by the cover slides, solar cells, metallic interconnects and insulating substrate. When exposed to a substorm environment, the cover slides become less negatively charged than the spacecraft ground. Hence, it is possible for metallic surfaces (usually silver mesh) to be at a negative potential in a cavity that has a 'positive' surface above it. If the resultant electric field becomes large enough, then the interconnect could emit electrons (probably by field emission) which could be accelerated to space by the positive voltage on the covers. An experimental study was connected using a small solar array segment in which the interconnect potential was controlled by a power supply while the cover slides were irridated by monoenergetic electrons. It was found that discharges could be triggered when the interconnect potential became at least 500 volts negative with respect to the cover slides. Analytical modeling of satellites exposed to substorm environments indicates that such gradients are possible. Therefore, it appears that this trigger mechanism for discharges is possible. Details of the experiment and modeling study are presented.

Stevens, N. J.↗

NASA NTRS1981

Low luminosity galactic X-ray sources

Models of soft X-ray emission from low-luminosity galactic X-ray sources are compared with currently available data. Emphasis is placed on disk population stars, irrespective of source temperatures spectral type, luminosity class, and age; and predictions of source temperatures and variability have been used to distinguish between the various models. It is tentatively found that the X-ray emission characteristics of late and early spectral types, and young and old stars, share many similarities; an economical explanation for this is the manifestation of coronal surface activity modulated by the stellar parameters that govern stellar magnetic activity (e.g., rotation). In some cases (such as for OB stars), a proper theory accounting for the heating of the coronal plasma does not exist.

Vaiana, G. S.↗

NASA NTRS1981

CTB80 - A galactic radio source with directed jets

Recent investigations of the galactic radio source CTB 80 reveal several jet-like structures which can be traced outward to over 30 pc from a point less than 0.1 pc within a central core. If the object is associated with a supernova of 1408, then the jets must move out at a velocity of 0.2 C and can only be about 572 years old. The morphology of the whole source, however, suggests a significant, proper east to west motion of the central object, and indicates a much older age. In this case, continuous ejection into the jets would have occurred for tens of thousands of years. A quantitative explanation is presented in which the supernova explosion ejects several massive path-cutting fragments. It thus appears that the extended jets in CTB 80 do emanate from a small core which is energized by a compact object, but the source of this continuous ejection process still remains unknown

Dickel, J. R.↗

NASA NTRS1981

Mars - Far-infrared spectra and thermal-emission models

Spectra of Mars from 100 to 360 kaysers were obtained during three different observation periods from NASA's Kuiper Airborne Observatory. Also, a new thermal model was constructed for the surface of Mars, and synthetic spectra were computed from the models to compare with the observations. The models include the effects of a dusty atmosphere which absorbs, scatters, and reradiates energy. The synthetic spectra show significant effects on disk-averaged brightness temperatures, as well as absorption features due to silicate dust. The spectra of Mars, which are ratios of Mars to the moon, do not fit the synthetic spectra unless the surface emissivities of Mars and the moon have different dependencies on wavelength. A possible explanation for this behavior is a difference in soil particle-size distributions between Mars and the moon, with Mars being depleted in large particles compared to the moon. Small particles are consistent with clay minerals which have been suggested elsewhere as constituents of the Martian surface.

Simpson, J. P.↗