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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 253 records · Page 14
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NASA NTRS1987

Nucleus of comet Halley as a torque-free rigid rotator

A model for the rotation of the nucleus of comet Halley is proposed on the assumption that the nucleus is homogeneous and a torque-free rigid rotator. It spins about its long axis with a period of 7.4 days, while this axis precesses about a fixed direction with a period of 2.2 days. To satisfy the moments of inertia, the precession angle must be 77 deg. This model settles the major problems associated with the recent controversy about two rotation periods.

Sekanina, Z.↗
NASA NTRS1987

Structure in the nucleus of NGC 1068 at 10 microns

New 8-13 micron array camera images of the central kiloparsec of Seyfert 2 galaxy NGC 1068 resolve structure that is similar to that observed at visible and radio wavelengths. The images reveal an infrared source which is extended and asymmetric, with its long axis oriented at P.A. 33 deg. Maps of the spatial distribution of 8-13 micron color temperature and warm dust opacity are derived from the multiwavelength infrared images. The results suggest that there exist two pointlike luminosity sources in the central region of NGC 1068, with the brighter source at the nucleus and the fainter one some 100 pc to the northeast. This geometry strengthens the possibility that the 10 micron emission observed from grains in the nucleus is powered by a nonthermal source. In the context of earlier visible and radio studies, these results considerably strengthen the case for jet-induced star formation in NGC 1068.

Tresch-Fienberg, R.↗
NASA NTRS1986

On the search for trajectories for a cometary nucleus sample return mission

The steps in the procedure for the generation of single trajectories for a comet nucleus sample return mission described by Stuhlinger et al. (1985) are discussed. The following assumptions are made for such a mission: (1) the spacecraft is equipped with an ion propulsion system supplied by solar cells, and (2) the comet has a low inclination and a period of about six years. The calculation of a specific trajectory incorporates the following main parameters: (1) the spacecraft mass at the beginning of the mission and the hyperbolic excess velocity, (2) the mass as a function of the injection energy, and (3) the available thrust level. The limitation of a supply of solar electric power to the region within 3 AU of the sun and the placement of permanent in-situ experiments at the comet are discussed. It is concluded that single trajectories for a nucleus sample return mission can be generated. A further step would be an integration of single solutions into classes of trajectories.

Schobert, D.↗
NASA NTRS1987

Narrowband imaging and spectroscopy close to the nucleus of the Seyfert galaxy NGC 7682

Keel's (1985) report of a jet-like optical feature emanating from the nucleus of NGC 7682 is investigated. Deep CCD images of NGC 7682 were taken with narrowband filters centered on the redshifted wavelength of H-alpha + forbidden N II and on a nearby continuum region. The continuum-subtracted line images show no evidence of the jet feature, although numerous H II regions appear clearly, both close to the nucleus and in the extended spiral arm structure. Spectra were taken at various dispersions and position angles, including the supposed position angle of the jet. These data were used to obtain background-subtracted spectra at the precise location of the jet. No excess emission was detected above the background-galaxy contribution. The highest-resolution spectra were used to determine the redshift of the galaxy to high precision.

Brodie, Jean↗
NASA NTRS1987

Infrared emission from young stars in the nucleus of M82

New observational and analytical techniques were used to obtain high-resolution NIR and FIR profiles of the luminous peculiar galaxy M82. The strongest NIR emission is found to be coincident with the dynamical center of the galaxy; a secondary NIR source, a factor of two fainter than the nucleus, is located 10 deg to the southewest. Simultaneous 40-micron and 100-micron profiles of M82 reveal an asymmetric distribution, with peak FIR emission diplaced about 5 arcsec to the west of center, and a plateau of emission extending about 5 arcsec to the east. The best positional determination indicates that the peak FIR emission from M82 is coincident with a cluster of young stars located to the southwest of the galactic nucleus at a projected distance of 10 arcsec (150 pc).

Joy, Marshall↗
NASA NTRS1987

Far-infrared continuum emission from the nucleus, starburst, and extended spiral arms of NGC 1068

Far-infrared slit scans across NGC 1068 are used to better define the contribution of the active nucleus, starburst disk, and extended spiral arms in the luminous output of this bright Seyfert 2 galaxy. The decomposition of the emission from the bright, inner 3 kpc of this galaxy suggests that at 50 microns, about half the emission is from star formation in a starburst disk and half from the compact, centrally heated circumnuclear cloud. The 100-micron profile of the starburst disk is asymmetric with respect to the nucleus. This appears to be the result of an extraordinary star-forming complex about a kiloparsec away from the center. With the application of maximum entropy deconvolution to the scans, evidence is found for 100-micron emission from the extended spiral arms of the galaxy. The far-infrared emission from the starburst region is distinguished from that of the extended spiral arms. In terms of both total luminosity and surface brightness, the extended spiral arms of NGC 1068 are at the bright end of the range of far-infrared emission from quiescent, noninteracting spirals.

Lester, D. F.↗
NASA NTRS1988

The morphology of multiple-nucleus brightest cluster galaxies

The morphology of high SNR CCD images of 16 multiple-nucleus brightest cluster galaxies is studied using an algorithm that models images of the systems as the line-of-sight superposition of normal elliptical galaxies. The algorithm is applied initially to the classic multiple-nucleus cD galaxy in A2199. Evidence is found suggestive of deep interpenetrating high-speed encounters by its secondaries. The interactions effects studied include noncentric isophotes, brightness profile effects, excess light around primary galaxies, and dynamical friction wakes. The results show that in many cases multiple systems are interacting systems.

Lauer, Tod R.↗
NASA NTRS1988

Evidence for a radio flare in the nucleus of Virgo A

An increase in radio emission has been observed in the nucleus of the galaxy Virgo A by use of VLBI measurements. These 2.29 GHz observations show that the correlated flux density of the milliarcsec structure increased by 30 percent during a four month period in 1977, and eventually returned to the preflare level of about 0.6 Jy. Previous evidence had indicated that the nuclear radio emission was stable, a surprising result for an active galactic nucleus.

Morabito, David D.↗
NASA NTRS1989

Kaon-nucleus scattering

The derivations of the Lippmann-Schwinger equation and Watson multiple scattering are given. A simple optical potential is found to be the first term of that series. The number density distribution models of the nucleus, harmonic well, and Woods-Saxon are used without t-matrix taken from the scattering experiments. The parameterized two-body inputs, which are kaon-nucleon total cross sections, elastic slope parameters, and the ratio of the real to the imaginary part of the forward elastic scattering amplitude, are presented. The eikonal approximation was chosen as our solution method to estimate the total and absorptive cross sections for the kaon-nucleus scattering.

Hong, Byungsik↗
NASA NTRS1988

Outgassing asymmetry of periodic Comet Encke. II - Apparitions 1868-1918 and a study of the nucleus evolution

Directed outgassing from isolated sources on P/Encke's rotating nucleus is investigated based on observations made between 1868 and 1918. A model of a collimated particle flow which identifies a sunward fan-like coma with the emission cone described by the ejecta from a discrete active region is shown to account for physical observations of the comet's perihelion. The results support nucleus precession, with a time-variable rate averaging about 1 degree per revolution. It is suggested that wall collapse and other processes limit the lifespans of individual vents to only a few hundred years or so. Differences between new and old vents are considered.

Sekanina, Z.↗
NASA NTRS1988

A model for intensity profiles of dust jets near the nucleus of Comet Halley

The Giotto spacecraft's Halley Multicolor Camera images have been used to derive intensity profiles of the jetlike dust features that are associated with active regions of the Comet Halley nucleus. An intensity profile's asymptotic behavior at a radius greater than 100 km from the nucleus can be seen as arising from a source located at a hypothetical point below the active source region. Several source distributions are investigated. The extended source model considers divergent dust flow from an active area of arbitrary shape. It is concluded that the surface is neither smooth nor homogeneous, but must instead be characterized by varying curvature and roughness in order to reflect the observed conical dust flow.

Huebner, W. F.↗
NASA NTRS1989

Active polar region on the nucleus of Comet Halley

The images of the nucleus of Comet Halley returned by the Giotto spacecraft reveal a number of active regions on the surface, one of which is near the expected location of the rotation pole. This feature is larger and brighter than other source regions, suggesting that the mechanism that drives this source is also different. At this active region near the rotation pole, the sun was circumpolar for a significant portion of the solar encounter. Continuous insolation heated the nucleus to greater depths than in other areas, producing the broad, active polar region.

Reitsema, H. J.↗
NASA NTRS1989

The double-nucleus galaxy IRAS 02580-1136 - A merging system

CCD imaging, infrared photometry, and optical spectroscopy lead to the conclusion that IRAS 02580-1136 consists of two colliding galaxies and is possibly an ongoing merger. Visually, the IRAS source displays two distinct brightness concentrations. These two nuclei, referred to as A and B, have a projected linear separation of 7 kpc and a radial-velocity difference of 180 km/s. Nucleus A belongs to a bulgelike structure and has an optical spectrum typical of a Seyfert 2. It is argued that it harbors a 99 percent dust-obscured low-luminosity Seyfert I source that powers most of the far-infrared radiation. Nucleus B is either a galactic bulge or a low-luminosity elliptical with a heavily reddened compact H II region at its center.

Heisler, Charlene A.↗
NASA NTRS1988

Anatomical evidence for red nucleus projections to motoneuronal cell groups in the spinal cord of the monkey

In four rhesus monkeys wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injections were made in the mesencephalic tegmentum. In three cases with injections involving the red nucleus (RN), rubrospinal fibers descended mainly contralaterally to terminate in laminae V, VI and dorsal VII of the spinal cord and in the lateral motoneuronal cell groups at the level of the cervical and lumbosacral enlargements. In all four cases the area of the interstitial nucleus of Cajal (INC) was injected, which resulted in labeled interstitiospinal fibers in the medial part of the ipsilateral ventral funiculus of the spinal cord. The results indicate that there is no major qualitative difference between the mesencephalic (RN and INC) and motor cortical projections to the spinal cord.

Holstege, Gert↗
NASA NTRS1989

Analysis of organic compounds in returned comet nucleus samples

Techniques for analysis of organic compounds in returned comet nucleus samples are described. Interstellar, chondritic and transitional organic components are discussed. Appropriate sampling procedures will be essential to the success of these analyses. It will be necessary to return samples that represent all the various regimes found in the nucleus, e.g., a complete core, volatile components (deep interior), and crustal components (surface minerals, rocks, processed organics such as macromolecular carbon and polymers). Furthermore, sampling, storage, return, and distribution of samples must be done under conditions that preclude contamination of the samples by terrestrial matter.

Cronin, J. R.↗
NASA NTRS1989

Thermal histories of the samples of two KOSI comet nucleus simulation experiments

Temperatures recorded during two KOSI comet nucleus simulation experiments strongly suggest that heat transport by vapor flow into the interior of the sample is very important. Two comet nucleus simulation experiments have been done by the KOSI team in a big space simulator. The thermal evolution of the sample during insolation and the results of simplified thermal evolution calculations are discussed. The observed thermal histories cannot be explained by a simple model with heat transferred by heat conduction at a constant conductivity, so a coupled heat and mass transfer problem was considered. The porous ice matrix was assumed to have a constant thermal conductivity and to be in thermal equilibrium with vapor in the pores, the internal pressure being the vapor pressure. The vapor was modelled as an ideal gas because, at the temperatures relevant to the problem, the mean free path length of the vapor molecules is large in comparison with the pore dimensions. The heat capacity at constant volume per unit mass of the two phase mixture was also assumed constant. The vapor was allowed to flow and transfer heat in response to an internal pressure gradient.

Spohn, T.↗
NASA NTRS1989

Methods for the mineralogical and textural analysis of comet nucleus samples

The objectives and instrumental requirements of a petrographic analysis of porous comet nucleus material are reviewed. Assumptions about its composition and texture, and the available techniques for the microscopic analysis of comet analogue material are investigated. New techniques required for the petrographic investigation of natural and artificial comet nucleus samples are also considered.

Stoeffler, D.↗
NASA NTRS1989

The nucleus of Comet P/Tempel 2

Simultaneous optical photometry and IR radiometry of Comet P/Tempel 2 are presented. Periodic variations of brightness are present and in phase at all wavelengths. Because the optical and thermal rotational light curves are in phase, it is concluded that the variations are caused by the changing apparent cross section of an elongated nucleus rotating with a period near 8.9 h. The variation of flux with aperture makes it possible to separate the contributions of the nucleus and the coma. The contribution by the coma is about 25 percent at maximum light in the optical and undetectable at the level of 10 percent at all times in the thermal IR.

A'Hearn, Michael F.↗