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NASA NTRS1983

Measurements of natural ice nuclei with a continuous flow diffusion chamber

A description is given of a continuous flow diffusion chamber technique for measuring the atmospheric concentrations of natural C-F nuclei. It is noted that the same device can also measure deposition nuclei; these two modes can thus be separated and compared. The laminar flow characteristics allow the temperature and supersaturation to be calculated with a high degree of precision and confidence. The method avoids the problems of a supporting substrate and of concentrating the sample into a small volume (as for membrane filters). The present measurements of natural ice nucleus concentrations at +1 percent water supersaturation are found to be comparable to research aircraft measurements of ice crystal concentrations in winter cap clouds over Elk Mountain, Wyoming (Vali et al., 1982).

Rogers, D. C.↗

NASA NTRS1984

Spectral components at visual and infrared wavelengths in active galactic nuclei

Aperture-dependent infrared photometry of active galactic nuclei are presented which illustrate the importance of eliminating starlight of the galaxy in order to obtain the intrinsic spectral distribution of the active nuclei. Separate components of emission are required to explain the infrared emission with a spectral index of alpha approx = 2 and the typical visual-ultraviolet continuum with alpha approx = 0.3 (where F(nu) varies as nu(sup-alpha). Present evidence does not allow unique determination of the appropriate mechanisms, but the characteristics of each are discussed.

Stein, W. A.↗

NASA NTRS1985

Consequences of hot gas in the broad line region of active galactic nuclei

Models for hot gas in the broad line region of active galactic nuclei are discussed. The results of the two phase equilibrium models for confinement of broad line clouds by Compton heated gas are used to show that high luminosity quasars are expected to show Fe XXVI L alpha line absorption which will be observed with spectrometers such as those planned for the future X-ray spectroscopy experiments. Two phase equilibrium models also predict that the gas in the broad line clouds and the confining medium may be Compton thick. It is shown that the combined effects of Comptonization and photoabsorption can suppress both the broad emission lines and X-rays in the Einstein and HEAO-1 energy bands. The observed properties of such Compton thick active galaxies are expected to be similar to those of Seyfert 2 nuclei. The implications for polarization and variability are also discussed.

Kallman, T.↗

NASA NTRS1985

Test results from a comparative evaluation of a condensation nuclei fire detector

The fire/smoke alarm response of a condensation nuclei fire detector (CNFD) was compared with photoelectric and ionization detectors. Tests were conducted in a former control room 8.5 m by 8.9 with a 2.7 m ceiling. The room had air supplied from above the ceiling and under the floor with return air exiting from ceiling grills. The environment was varied from 278 to 305 K and relative humidities from 8 to 65%. Four detection zones were located in the room. Each zone contained a sampling head for the CNDF, a photodetector, and an ionization detector so that each detector system had four opportunities to alarm during tests. The particle level in the test room was also monitored during tests with a condensation nuclei particle counter. The CNFD responded to 90% of exposures to smoldering plastic and 84% of exposures to visible fire. The photoelectric response was 43 and 12.5% respectively for the same conditions. The ionization response was 9 and 48 respectively.

Bricker, R. W.↗

NASA NTRS1985

Surfaces of Asteroids and Cometary Nuclei

The types of landforms and processes that may exist on cometary nuclei and asteroidal surfaces are investigated. Acknowledging that some asteroids may be cometary nuclei in disguise, asteroids are treated in this report as a simpler case than comets, owing to their more limited response to the state environment. Larger bodies (D 100 km) will not be discussed, even though they are recognized to be extremely important. This limitation permits only processes depending on exogenic phenomena to be considered (excluding processes such as volcanism on Vesta, for example), thus focusing discussion on the more unique aspects of these bodies, namely, their size and number.

Malin, M. C.↗

NASA NTRS1985

The response of ionization chambers to relativistic heavy nuclei

As part of a recent calibration at the LBL Bevalac for the Heavy Nuclei Experiment on HEAO-3, the response of a set of laboratory ionization chambers were compared to beams of 26Fe, 36 Kr, 54Xe, 67 Ho, and 79 Au nuclei at maximum energies ranging from 1666 MeV/amu for Fe to 1049 MeV/amu for Au. The response of these chambers shows a significant deviation from the expected energy dependence, but only a slight deviation from Z squared scaling.

Newport, B. J.↗

NASA NTRS1985

Absolute rigidity spectrum of protons and helium nuclei above 10 GV/c

Proton and helium nuclei differential spectra were gathered with a balloon borne magnet spectrometer. The data were fitted to the assumption that the differential flux can be represented by a power law in rigidity. In the rigidity range 10 to 25 GV/c the spectral indices were found to be -(2.74 plus or minus 0.04) for protons and -(2.71 plus or minus 0.05) for helium nuclei. A brief discussion is given by systematic errors.

Golden, R. L.↗

NASA NTRS1985

The response of ionization chambers to relativistic heavy nuclei

The LBL Bevalac for the Heavy Nuclei Experiment on HEAO-3, compared the response of a set of laboratory ionization chambers to beams of 26Fe, 36Kr, 54Xe, 67 Ho, and 79Au nuclei at maximum energies ranging from 1666 MeV/amu for Fe to 1049 MeV/amu for Au. The response of these chambers shows a significant deviation from the expected energy dependence, but only a slight deviation from Z sq scaling.

Newport, B. J.↗

NASA NTRS1983

Fragmentation of 710 and 1050 MeV/nuc Fe nuclei in CH2 and C targets - Isotopic cross sections for H targets

Fe nuclei of incident energies of 710 and 1050 MeV/nuc in CH2 and C targets are fragmented in order to measure isotopic cross sections in hydrogen targets. The telescope used to measure the charge and mass of the fragments is a Cerenkov x total energy telescope. The data are reported for z = 20-25 fragments. The number of individual events corresponding to each charged fragment is obtained and analyzed. Ratios of partial cross sections on C and CH2 targets indicate that simple scaling exists for isotope fractions as well as for charge fractions in different targets. The cross sections in hydrogen are obtained directly by a simple subtraction. Excitation functions for Mn and Cr nuclei are presented.

Webber, W. R.↗

NASA NTRS1983

Interactions of 200 GeV gold nuclei in light elements

Total charge-changing cross sections and partial cross-sections for interactions of 200 GeV Au-197 nuclei incident on carbon and polyethylene (CH2) targets have been measured during a calibration of the HEAO-3 Heavy Nuclei Experiment. From these, the total and partial cross-sections for Au-197 incident on hydrogen are inferred. The effects of using these cross-sections in one model of cosmic ray propagation are illustrated. Comparisons to predictions using semi-empirical formulas are shown.

Brewster, N. R.↗

NASA NTRS1985

Multiaperture infrared photometry of the nuclei of spiral galaxies

Results of a multiaperture, 2.2- and 10-micron photometric survey of the nuclei of 25 nearby, low-inclination spiral galaxies are presented. The 10-micron nuclear luminosities, attributed to thermal reradiation by dust in regions of active star formation, and 10-micron/2.2-micron nuclear flux ratios, are examined as a function of the slope of 2.2-micron growth curve. No correlation is seen, suggesting that the contribution of young, red giants and supergiants to the near-infrared light of spiral nuclei is small. These results indicate that the 2.2-micron light of galaxies in the present sample is not radically altered by starbursts.

Cizdziel, P. J.↗

NASA NTRS1985

Consequences of hot gas in the broad-line region of active galactic nuclei

Kallman, T.↗

NASA NTRS1985

Balloon-borne observation of Aitken nuclei in the Antarctic stratosphere and troposphere

Aitken nuclei (0.002 or = r or = 0.1 microns in the atmosphere are produced through gas-to-particle conversion processes, and they grow in size by heterogeneous nucleation processes and others to produce larger aerosol particles. In the study of global background aerosol pollution, full knowledge of such aerosol processes in the clean atmosphere is essentially required. In this sense, it is important to examine the behavior of aerosols in a clean atmosphere which is not contaminated directly by aerosols and gases emitted from the Earth's surface. The Antarctic atmosphere is thought to be such a clean atmosphere. From an extensive surface observation of aerosols carried out at Syowa Station (69 deg 00'S, 39 deg 35'E) Antarctica, it has been revealed that various phenomena relating to long-range transport of trace constituents and/or photochemical processes resulting in production or growth of aerosol particles are clearly observed in Antarctica. This paper gives a preliminary report of observations made by balloon-borne Aitken nuclei sonde in 1983, at Syowa Station.

Ito, T.↗

NASA NTRS1985

Amorphous and porous ices in cometary nuclei

The heat flux into the cometary nucleus before and after perihelion and its influence on the nucleus are discussed. The surface temperature and the associated rate of evaporation are lower than usually calculated, and the effect is strongly dependent on the porosity of the nucleus. The surface temperature reaches a maximum after perihelion, in agreement with statistical studies of comae and tails. Delayed heating of the CO2-rich inclusions deep in the nucleus leads to outbursts and splittings as far as 9 AU after perihelion, also in agreement with observation. At sufficiently high temperatures, heat transport in porous cometary nuclei is controlled by vapor diffusion. The presence of CO2 vapor in the pores significantly increases the heat flow in mixed nuclei at temperatures above 140-150 C. Closed pores move up the radial thermal gradient so that the outside layer of a cometary nucleus should become denser.

Smoluchowski, R.↗

NASA NTRS1986

On the relationship between optically selected and X-ray-selected active galactic nuclei

Available information on the optically selected active galactic nuclei (AGNs) (luminosity function, cosmological evolution, etc.), together with the knowledge of their X-ray to optical luminosity ratio, are used to predict the overall properties of X-ray-selected active galactic nuclei (number counts, evolution, luminosity and redshift distributions, etc.). The predicted properties are then compared with those observed. Similarly, predictions are carried out for the optical properties of the X-ray-selected AGN parent population. In the search for a possibility explanation for discrepancies, preliminary results are reported.

Franceschini, A.↗

NASA NTRS1986

Studies of the composition of solar particles and of energetic oxygen and sulfur nuclei trapped in the Jovian magnetosphere

The Cosmic Ray System (CRS) experiment on board each of the Voyager 1 and 2 spacecraft consists of four Low Energy Telescopes (LETs), two High Energy Telescopes (HETs), the Electron Telescope (TET), and associated electronics. With these instruments it is possible to measure the energy spectrum of electrons over the 3-110MeV energy range and the energy spectra and nuclear charge of atomic nuclei from hydrogen through zinc over the 3-500 MeV/nuc energy range. The exclusive use of solid-state detectors in the CRS telescopes achieves the objectives of reliability over a long mission life, high resolution determinations of energy and charge, and high-count-rate capability during large solar flares and passage through the magnetospheres of the outer planets. Summarized here are some of the many accomplishments that have resulted from the CRS measurements during the period covered by this report, May 15, 1981 to May 15, 1984, including studies of the energetic oxygen and sulfur nuclei trapped in the Jovian magnetosphere.

Stone, E. C.↗

NASA NTRS1987

The relation between star formation and active nuclei

Three questions relevant to the relation between an active nucleus and surrounding star formation are discussed. The infrared stellar CO absorption bands can be used to identify galaxies with large populations of young, massive stars and thus can identify strong starburst unambiguously, such as in NGC 6240, and can help identify composite active/starburst systems such as Arp 220. An active nucleus is probably not required for LINER spectral characteristics; dusty starburst galaxies, particularly if they are nearly edge-on, can produce LINER spectra through the shock heating of their interstellar media by supernovae combined with the obscuration of their nuclei in the optical. The Galactic Center would be an ideal laboratory for studying the interaction of starbursts and active nuclei, if both could be demonstrated to occur there. Failure to detect a cusp in the stellar distribution raises questions about the presence of an active nucleus, which should be answered by additional observations in the near future.

Rieke, G. H.↗

NASA NTRS1987

Models relating the radio emission and ionised gas in Seyfert nuclei

Possible models are discussed in which the radio emitting components in Seyfert II nuclei can compress and accelerate the ambient nuclear medium to produce the characteristics of the narrow line region. A first order model, which considers only the expansion of the radio components, is briefly described. However, in many Seyfert nuclei it appears that the linear motion of the radio components is also important. This can result in shock heating of the ambient medium, and if the cooling time is long enough, can lead to a displacement between the radio component and the associated emission lines. This effect may be present in NGC 1068 and NGC 5929 and by considering ram pressure balance and the cooling length it is possible to estimate lobe velocities and ambient densities.

Pedlar, A.↗