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NASA NTRS1985

Outer solar system materials - Ices and color systematics

Our program of VJHK colorimetric observations and spectrophotometry is reviewed and updated. Attention is given to the probable connections between VJHK colors and the ratios of bright ices and dark soils on many outer solar system small bodies' surfaces. VJHK color systematics may clarify ice/soil behaviors in bodies too faint for high resolution spectra. Comets appear colored by soils most closely resembling D-class Trojan asteroid soils. Our recent model of comet surface properties, involving weakly-bonded ice/soil regoliths, helps explain comet eruptive phenomena. The work suggests the importance of considering ices in the context of their intimate mixture with non-volatile soils.

Hartmann, W. K.↗
NASA NTRS1986

The ultraviolet excess of quasars. III - The highly polarized quasars PKS 0736 + 017 and PKS 1510 - 089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736 + 047 and PKS 1510 089 is analyzed. A blazer continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510 - 089, and at least three-quarters of that in 0736 + 017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510 - 089, and weakly detected in 0736 + 017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars.

Malkan, M. A.↗
NASA NTRS1986

Research in planetary astronomy and operation of the 2.2-meter telescope

The turn-around in the secular change in brightness of Pluto was detected, the planet is now beginning to brighten. The spectral signature was found of an ammonia bearing compound in the surface ices of Europa. Specific Io volcanic hotspots were detected from infrared photometry of the mutual events of the Jovian satellites. The polarized emission from the volcanic hotspots on Io was discovered and the locations of those hotspots were determined. The orbit of Charon was refined from speckle observations of the Pluto-Charon system. The spectral properties of liquid nitrogen-methane mixtures with reference to the infrared spectrum of Triton were studied. Major progress was made in modeling asteroid lightcurves from a modern theory of photometric properties of the asteroid surfaces. Several additional olivine-rich asteroids from near-infrared spectrophotometry were discovered. Important photometric, spectroscopic, narrow-band imaging data on Comet P/Halley was acquired, along with Schmidt photographs of Comet P/Halley and its tail.

Hall, D. N. B.↗
NASA NTRS1986

Physical processes in comets

Final revisions were made in the study of continuum spectrophotometry of 17 comets done at Lick Observatory. Changes based upon this study were introduced into the Divine-Newburn cometary modelling paradigm. Work was begun on modifications to all of the theory based upon the direct nucleus and coma observations made by the Halley space missions.

Newburn, R. L., Jr.↗
NASA NTRS1986

Physical properties of asteroids

The physical properties of asteroids were studied by telescopic observations and laboratory and theoretical work. Spectrophotometry from 0.3 to 1.1 microns and 1.2, 1.6 and 2.2 micron photometry allow spectral-compositional classification of asteroids. Based on laboratory data and telescopic observations, it was found that infrared measurements at 1.2, 1.6 and 2.2 microns provide a relatively rapid and accurate method for the classification of minor planets and are important in comparing asteroids with meteorites. This technique was proven and employed in an expanded survey of Apollo-Amor-Aten and other unusual asteroids recently scanned by IRAS.

Veeder, G. J.↗
NASA NTRS1986

Infrared reflection nebulae in Orion molecular cloud 2

New obervations of Orion Molecular Cloud-2 have been made from 1-100 microns using the NASA Infrared Telescope Facility and the Kuiper Airborne Observatory. An extensive program of polarimetry, photometry and spectrophotometry has shown that the extended emission regions associated with two of the previously known near infrared sources, IRS1 and IRS4, are infrared reflection nebulae, and that the compact sources IRS1 and IRS4 are the main luminosity sources in the cloud. The constraints from the far infrared observations and an analysis of the scattered light from the IRS1 nebula show that OMC-2/IRS1 can be characterized by L less than or equal to 500 Solar luminosities and T approx. 1000 K. The near infrared (1-5) micron albedo of the grains in the IRS1 nebula is greater than 0.08.

Pendleton, Y.↗
NASA NTRS1986

Unstable 06.5f?p star HD 148937 and its interstellar environment

The massive, early-type star HD 148937 (spectral type 06.5?p) is surrounded by a unique set of nebulosities. A spherically symmetric Stromgren sphere (Radius approx. - 25 pc), an ellipsoidal filamentary nebulosity (semimajor axis approx. - 5 pc) interpreted as a stellar-wind-blown shell, and a bipolar nebular complex (semimajor axis approx. - 1 pc) with HD 148937 located in the apparent center of symmetry. Observations of these nebulosities are reported (narrow-band charge coupled devices imaging, image dissector scanner (IDS) spectrophotometry, high resolution spectroscopy) in an attempt to establish a consistent model of HD 148937 and its nebulosities.

Leitherer, C.↗
NASA NTRS1986

A Lambda 1400 spectrophotometric census of the Orion belt region

Low dispersion IUE spectrophotometry were used to generate a pair of photometric indices which measure the strength of the broad continuum absorption feature at 1400 A, likely an autoionizing transition of Si II. Calibration of the indices as identifiers of silicon overabundance is based on measurements of 25 IUE spectral standards and a sample of O8-A0 IV-V stars, 18 of them silicon stars. The correlations of delta alpha 1400 with delta alpha 5200 and delta (VI-G) support the association of the lambda 5200 feature with silicon. Using this technique, a magnitude limited survey of 28 B-stars in sub-groups b1, b2 and b3 of the Orion OB1 association was conducted. Two previously unrecognized candidate (perhaps weakly overabundant) silicon stars, HD 37187 and BD - 0 deg 984 are identified.

Brown, Douglas N.↗
NASA NTRS1987

Effect of an oxygen plasma on uncoated thin aluminum reflecting films

Thin aluminum films were considered for use as a reflective surface for solar collectors on orbiting solar dynamic power systems. A matter of concern is the durability of such reflective coatings against oxidative attack by highly reactive neutral atomic oxygen, which is the predominate chemical specie in low Earth orbit. Research to date was aimed at evaluating the protective merit of thin dielectric coatings over the aluminum or other reflective metals. However, an uncoated aluminum reflector may self-protect by virtue of the oxide formed from its exposed surface, which constitutes a physical barrier to further oxidation. This possibility was investigated, and an attempt was made to characterize the effects of atomic oxygen on thin Al films using photomicrographs, scanning electron microscopy, spectrophotometry, Auger analysis, and mass measurements. Data collected in a parallel effort is discussed for its comparative value. The results of the investigation of uncoated aluminum supported the self-protection hypothesis, and importantly, it was found that long term specular reflectance for uncoated aluminum exceeded that of Al and Ag reflectors with dielectric coatings.

Parsons, Roger L.↗
NASA NTRS1987

The 1986 DA and 1986 EB: M-class asteroids in near-Earth orbits

The Earth-approaching asteroid population is composed of asteroids in orbits with short lifetimes compared with the age of the solar system. These objects which are comprised of Aten, Apollo, and Amor asteroids must be replenished from either cometary or mainbelt asteroid sources since lifetimes against collision with or ejection by a planet are on the order of 10 to 100 million years. The physical study of Earth-approaching asteroids is constrained by the generally long period between favorable apparitions and poorly known orbits. Broadband spectrophotometry on the Johnson UBVR system and the Eight-Color Asteroid Survey system were obtained at Kitt Peak National Observatory and on the Johnson JHK system and at 10 and 20 microns at the NASA Infrared Telescope Facility at Mauna Kea Observatory. These observations were used to determine the absolute visual magnitudes and to derive the visual geometric albedos and diameters on the IRAS system. The spectral reflectance properties and geometric albedos of the M-class asteroids are consistent compositions analogous to the iron nickel meteorites or the enstatite-metal assemblages of the enstatite chondrites. The issue of the source(s) of the near-Earth asteroids population was examined by comparing the classifications on the scheme employed by Gradie and Tedesco of 38 such asteroids. Most of the near-Earth objects is indeed the asteroid belt as the observations suggest, then a method for removing extinct nuclei of short period comets must be found since the rate of production of short period comets from the long period comets is relatively large.

Gradie, Jonathan↗
NASA NTRS1987

Sulfur-oxygen processes on Io

Laboratory studies of irradiated sulfur dioxide frost have found that sulfur trioxide should be formed as a consequence of the irradiation process. The spectral reflectance of solid sulfur trioxide was measured in the laboratory and it was found that the compound has strong absorption features at 3.37 and 3.70 microns. These features are not present in the spectral geometric albedo of Io. This is interpreted as an indication that sulfur trioxide may exist in such limited abundance that it is undetectable in disk averaged spectrophotometry. It is suggested that the Near-Infrared Mapping Spectrometer on the Galileo spacecraft should be able to identify condensed sulfur trioxide on Io particularly in regions bordering the sulfur dioxide deposits. The presence of elemental sulfur on Io's surface has been questioned on several grounds, most notably the suggested production process (quenched molten sulfur extrusions) and the effect of radiation (particularly X-rays) on some of the allotropes. Mixtures of sulfur allotropes were produced in the laboratory by quenching molten sulfur and it was found that the spectra indicate the presence of certain red-colored allotropes which are preserved upon quenching. The color of the sulfur glass produced is redder when the temperature of the original melt is higher. This is consistent with the suggestion that Io's spectral geometric albedo can be partly explained by the presence of quenched sulfur glasses.

Nelson, Robert M.↗
NASA NTRS1987

Infrared-ultraviolet spectra of active galactic nuclei

Data from IRAS and IUE were combined with ground based optical and infrared spectrophotometry to derive emission line free spectral energy distributions (SEDs) for 29 active galactic nuclei (AGNs) between 0.1 and 100 microns. The IRAS data were scaled down to account for extended emission. These correction factors, determined by comparing small aperture ground based 10.6 micron data with large aperture IRAS 12 micron fluxes, were usually less than 25%. These corrected SEDs are shown.

Malkan, M. A.↗
NASA NTRS1986

Oxygen production rates for P/Halley over much of the 1985-1986 apparition

Long slit CCD spectrophotometry of comet P/Halley in the visible region was used to measure the production rate of atomic oxygen during the 1985/86 apparition. The observations cover a large range of heliocentric distances, since the technique is applicable to apparently bright and faint comets. The cometary gas production rate for P/Halley increases rapidly with decreasing heliocentric distance toward perihelion and is systematicaly larger at a given heliocentric distance for the postperihelion observations. The average production rate for O1D on the day of the Giotto flyby is 4 times 10 to the 28th power atoms/sec giving an extrapolated total water production rate of 6 times 10 to the 29th power mols/sec. A method for comparing the absolute cometary gas production rates for different comets is discussed.

Spinrad, Hyron↗
NASA NTRS1986

The infrared astronomical satellite asteroid database

The creation, maintenance, and distribution of the set of ground-based observational data being used to help calculate the diameters and albedos of asteroids observed by IRAS during the sky survey of February-November 1983 are discussed in a status report. The database comprises orbital elements, absolute magnitudes, UBV colors, thermal radiometry, light-curve parameters, and taxonomic classifications; supplementary files include eight-color photometry, spectrophotometry, polarimetry, JHK observations, proper elements, discovery data, occultation diameters, radar characteristics, and references. Distribution in machine-readable and hard-copy formats and maintenance of the database by incorporating new data as they are published are planned.

Tedesco, E. F.↗
NASA NTRS1986

Spectral energy distributions of active galactic nuclei between 0.1 and 100 microns

The 0.1-100-micron line-free spectral energy distributions of 29 AGN are characterized by fitting simple models to data from IRAS and IUE observations and ground-based NIR and optical spectrophotometry. The data are presented in tables and graphs and discussed in detail. It is found that nuclear dust does not play a major role in most of the Seyfert 1 galaxies and QSOs, which can be described by a model with four spectral components.

Edelson, R. A.↗
NASA NTRS1986

Temperatures for hot and pulsating DB white dwarfs obtained with the IUE Observatory

Ultraviolet energy distributions are presented for 12 hot, helium-atmosphere DB white dwarfs, including the four known pulsating stars which define an empirical DB instability strip. The UV spectrophotometry is reported, and the energy distributions are matched with two separate grids of DB model atmosphere calculations, so that effective temperature estimates may be derived. The sources of uncertainty in the UV temperature fits are assessed, and a comparison with estimates from optical data is made.

Liebert, James↗
NASA NTRS1986

Variability of Markarian 1018 - Seyfert 1.9 to Seyfert 1

Simultaneous IUE and optical spectrophotometry of the Seyfert 1.9 galaxy Markarian 1018 is presented. The strength of H-beta(broad) has increased by a factor of 6.6 in 4 yr, and the galaxy now shows strong broad UV and optical line emission similar to that seen in normal Seyfert 1 galaxies, but with markedly asymmetric line profiles. As in other variable Seyfert galaxies, H-alpha emission has also increased but by a lesser amount than H-beta. Furthermore, Ly-alpha (not observed during the first epoch) is now quite strong relative to H-beta and H-alpha. Inspection of the line profiles reveals nearly identical blue asymmetric line profiles in all permitted lines; these show evidence of significant profile evolution over a 1 yr time scale. The present line ratios and the nature of their variability suggest that the enhancement in the broad-line emission is not caused by the removal of obscuring dust but by the 'lighting up' of the broad-line region.

Cohen, Ross D.↗
NASA NTRS1986

Infrared reflection nebulae in Orion Molecular Cloud 2

New observations of Orion Molecular Cloud 2 have been made from 1 to 100 microns using the NASA Infrared Telescope Facility and the Kuiper Airborne Observatory. An extensive program of polarimetry, photometry, and spectrophotometry has shown that the extended emission regions associated with two of the previously known near-infrared sources, IRS 1 and IRS 4, are infrared reflection nebulae, and that the compact sources IRS 1 and IRS 4 are the main luminosity sources in the cloud. The constraints from the far-infrared observations and an analysis of the scattered light from the IRS 1 nebula show that OMC-2/IRS 1 can be characterized by L of 500 solar luminosities or less and T of roughly 1000 K. The near-infrared albedo of the grains in the IRS 1 nebula is greater than 0.08.

Pendleton, Yvonne↗