Visible spectral reflectance measurements (0.33–1.1 μm) of the Galilean satellites at many orbital phase angles

One hundred eighty-seven reflectance spectra (0.33–1.10 μm) of the Galilean satellites have been obtained. Solar phase angle color correction coefficients were derived and the spectra corrected to a solar phase of 6°. Solar phase angle coefficients beyond 0.55 μm are presented for the first time. The spectra as a function of orbital phase angle are presented in the form of images to display hemispheric spectral variations. Io and Europa are redder on their trailing hemispheres while Callisto is redder on its leading hemisphere. Ganymede shows small longitudinal color variations despite the complex albedo structure visible in Voyager images. Comparisons of these data with previous measurements reveal that most differences can be attributed to the solar calibration. Reflectance measurements of Io at 0.73 μm observed 8.5 years apart show a 6% global reflectance decrease. However, it is difficult to unambigously attribute this particular decrease in reflectance to a change in Io's surface composition.     

Ubvri photometry of nova 1934 dq her during 1982–1995: Brightness variability

The principal results of a photometric investigation of Nova 1934 DQ Her during 1982–1995 are presented. Simultaneous high-speed UBVRI photometry was used to investigate for the first time the behavior of its brightness on time scales from several days to several years. Relationships are found between the changes in brightness of DQ Her in various regions of the spectrum and the corresponding changes in the energy distribution of its radiation. The observed variations in brightness of the system are caused by the variability in the radiation from the accretion disk with the white dwarf at the center. The brightness variations on the time scale of several days to several dozen days, may be caused by changes in the rate of accretion from the disk onto the white dwarf due to inherent disk instability or by irregular delivery of material in the jet from the red dwarf. Cyclic variations in brightness of DQ Her with an amplitude of several tenths of a magnitude and a characteristic time of about 5 yr, as well as the cyclic variations of the parameter "O-C" with the same characteristic time and amplitude of about 2–4 min may be the response of the accretion disk to activity of the red dwarf itself.Translated fromAstrofizika, Vol. 39, No. 1, pp. 41–55, January–March, 1996.     

The rings of Saturn: New near-infrared reflectance measurements and a 0.326–4.08 μm summary

A new high photometric precision reflectance spectrum of Saturn's rings covering the spectral region 0.65 to 2.5-μm is presented and three previously unreported absorption features at 1.25, 0.85, and probably 1.04 μm are identified. The 1.25- and 1.04-μm absorptions are due to water ice. The 0.85-μm feature may be due to a combination of 0.81- and 0.90-μm ice absorptions but this feature appears too strong relative to the 1.04-μm band to be completely explained by weater ice. Another possibility is that the 0.85-μm band is due to Fe³⁺-bearing minerals in an ice-mineral mixture. This explanation could also account for the drop in the visible and ultraviolet reflectance and the rise in reflectance around 3.6 μm. Finally, a composite spectrum from 0.325 to 4.08 μm is presented which will be useful for future analysis and laboratory studies.     

Spectral reflectance of Martian areas during the 1973 opposition: Photoelectric filter photometry 0.33–1.10 μm

Reflectance spectra of 26 Martian areas (200–400 km in diameter) that were measured during the 1973 opposition are presented. They were measured through 25 narrow-band interference filters between 0.33 and 1.10 μm, using a photoelectric filter photometer at the Mauna Kea 230-cm telescope. There were many more bright and dark areas observed than during previous oppositions, and for the first time spectra were obtained of dust clouds and areas of mixed and intermediate albedo. The bright areas and dust clouds were all apparently composed of the same mineralogic unit. The dark area spectra differed substantially from the bright area and dust cloud spectra, and they showed major regional variations. The spectra of mixed and intermediate albedo areas had absorption bands seen in both bright and dark area spectra, and did not display any unique new features: thus they were apparently not compositionally unique, but rather were probably composed of mixtures of high albedo dust and dark area soils.     

Spectral reflectance of solid sulfur trioxide (0.25–5.2 μm): Implications for Jupiter's satellite Io

We have measured the reflection spectrum of solid sulfur trioxide and we have compared this spectrum to the spectral geometric albedo of Jupiter's satellite Io. We find that the laboratory spectrum of solid SO₃ has very strong absorption features at 3.38, and 4.08 μm. The 3.38- and 3.70-μm absorptions are present very weakly (if indeed at all) in the spectral geometric albedo of Io. This suggests that solid SO₃, if present at all, could exist only as a very minor component of Io's surface. We note that studies involving particle bombardment of SO₂ (a known Io surface constituent) produce SO₃ (Moore, 1984, Icarus 31, 40–80). Sulfur trioxide, once formed on Io's surface, would be extremely stable; however, it would not be expected to accumulate to levels detectable from Earth-based instruments. While it may be possible that the constant resurfacing of Io by volcanic ejecta may cover any SO₃ formed, the area subject to such extensive resurfacing on short time scales (∼ 1 year) is at best ∼10%. Therefore, we would expect that condensed SO₂ remote from volcanos should develop a small but significant SO₃ concentration that could be detected by instruments such as the near-infrared mapping spectrometer on the Galileo spacecraft.     

Spectral reflectance change and luminescence of selected salts during 2–10 KeV proton bombardment: Implications for Io

Radiation damage and luminescence, caused by magnetospheric charged particles, have been suggested by several authors as mechanisms for explaining some of the peculiar spectral/albedo features of Io. We have pursued this possibility by measuring the uv-visual spectral reflectance and luminescent efficiency of several proposed Io surface constituents during 2 to 10-keV proton irradiation at room temperature and at low temperature (120 < T < 140°K). The spectral reflectance of NaCl and KCl during proton irradiation exhibits the well-known F-center absorption bands at 4580 and 5560 Å. Na₂SO₄ shows a generalized darkening which increases toward longer wavelengths. NaNO₃ shows a spectral reflectance change indicative of the partial alteration of NaNo₃ to NaNo₂. NaNO₂ shows no change. The luminescent efficiencies of NaCl and KCl are ～10^?4 at 300°K and increase by one-half order of magnitude at ～130°K. The efficiencies of K₂CO₃, Na₂CO₃, Na₂SO₄, and NaNO₃ are 10^?4, 10^?4, 10^?5 and 10^?6, respectively, at 300°K and they all decrease by one-half order of magnitude at ～130°K. These results indicate that magnetospheric proton irradiation of Io could cause spectral features in its observed ultraviolet and visible reflection spectrum if salts such as those studied here are present on its surface. However, because the magnitude of these spectral effects is dependent on competing factors such as surface temperature, incident particle energy flux, solar bleaching effects, and trace element abundance, we are unable at this time to make a quantitative estimate of the strength of these spectral effects on Io. The luminescent efficiencies of pure samples that we have studied in the laboratory suggest that charged-particle induced luminescence from Io's surface might be observable by a spacecraft such as Voyager when viewing Io's dark side.     

Solar EUV spectra obtained during the SPIRIT experiment onboard the CORONAS-F satellite: A catalog of lines in the range 176–207 Å

We present a catalog of 65 spectral lines in the range 176–207 Å recorded by the RES spectroheliograph in active regions and flares during the SPIRIT experiment onboard the CORONASF satellite. We have identified 51 lines. The relative intensities of lines recorded during the M6.5 (GOES) flare of September 16, 2001, are given. The data processing technique is discussed.     

Variety of well behaved exact solutions of Einstein–Maxwell field equations: an application to Strange Quark stars, Neutron stars and Pulsars

We present a variety of well behaved classes of Charge Analogues of Tolman’s iv (1939). These solutions describe charged fluid balls with positively finite central pressure, positively finite central density; their ratio is less than one and causality condition is obeyed at the centre. The outmarch of pressure, density, pressure-density ratio and the adiabatic speed of sound is monotonically decreasing, however, the electric intensity is monotonically increasing in nature. These solutions give us wide range of parameter for every positive value of n for which the solution is well behaved hence, suitable for modeling of super dense stars. keeping in view of well behaved nature of these solutions, one new class of solutions is being studied extensively. Moreover, this class of solutions gives us wide range of constant K (0.3≤K≤0.91) for which the solution is well behaved hence, suitable for modeling of super dense stars like Strange Quark stars, Neutron stars and Pulsars. For this class of solutions the mass of a star is maximized with all degree of suitability, compatible with Quark stars, Neutron stars and Pulsars. By assuming the surface density ρ _b =2×10¹⁴ g/cm³ (like, Brecher and Caporaso in Nature 259:377, 1976), corresponding to K=0.30 with X=0.39, the resulting well behaved model has the mass M=2.12M _Θ, radius r _b ≈15.27 km and moment of inertia I=4.482×10⁴⁵ g cm²; for K=0.4 with X=0.31, the resulting well behaved model has the mass M=1.80M _Θ, radius r _b ≈14.65 km and moment of inertia I=3.454×10⁴⁵ g cm²; and corresponding to K=0.91 with X=0.135, the resulting well behaved model has the mass M=0.83M _Θ, radius r _b ≈11.84 km and moment of inertia I=0.991×10⁴⁵ g cm². For n=0 we rediscovered Pant et al. (in Astrophys. Space Sci. 333:161, 2011b) well behaved solution. These values of masses and moment of inertia are found to be consistent with other models of Neutron stars and Pulsars available in the literature and are applicable for the Crab and the Vela Pulsars.     

Early Mars climate near the Noachian–Hesperian boundary: Independent evidence for cold conditions from basal melting of the south polar ice sheet (Dorsa Argentea Formation) and implications for valley network formation

Currently, and throughout much of the Amazonian, the mean annual surface temperatures of Mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold-based. The documented evidence for extensive and well-developed eskers (sediment-filled former sub-glacial meltwater channels) in the south circumpolar Dorsa Argentea Formation is an indication that basal melting and wet-based glaciation occurred at the South Pole near the Noachian–Hesperian boundary. We employ glacial accumulation and ice-flow models to distinguish between basal melting from bottom-up heat sources (elevated geothermal fluxes) and top-down induced basal melting (elevated atmospheric temperatures warming the ice). We show that under mean annual south polar atmospheric temperatures (?100 °C) simulated in typical Amazonian climate experiments and typical Noachian–Hesperian geothermal heat fluxes (45–65 mW/m²), south polar ice accumulations remain cold-based. In order to produce significant basal melting with these typical geothermal heat fluxes, the mean annual south polar atmospheric temperatures must be raised from today’s temperature at the surface (?100 °C) to the range of ?50 to ?75 °C. This mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water, and thus does not favor a “warm and wet” early Mars. Seasonal temperatures at lower latitudes, however, could range above the melting point of water, perhaps explaining the concurrent development of valley networks and open basin lakes in these areas. This treatment provides an independent estimate of the polar (and non-polar) surface temperatures near the Noachian–Hesperian boundary of Mars history and implies a cold and relatively dry Mars climate, similar to the Antarctic Dry Valleys, where seasonal melting forms transient streams and permanent ice-covered lakes in an otherwise hyperarid, hypothermal climate.     

Far infrared photometry of planets: Saturn and Venus: Volume 38, Number 3 (1979), in the article,by R. Courtin,P. Léna,M. De Muizon,D. Rouan,C. Nicollier,and J. Wijnbergen,pp. 411–419

The global distribution of existing lunar topography suffers from a lack of measurements of far-side radii because of the sparsity of data types in the nonequatorial regions. This paper presents determinations of far-side lunar radii based on the reduction of photogrammetric measurements derived from selected Apollo 16 trans-Earth phase photographs. The regions covered in this analysis lie west of Mare Moscoviense between longitudes 90 and 130°E and latitudes 10 and 60°N. The determinations are made using control points appearing on both NASA topographic orthophoto maps and the Apollo 16 photographs. The estimated lunar radii are referred to these control points and determined with a relative accuracy of 500 m. The new lunar radii are used to generate a topographic map covering the area investigated. The map shows that, with the given spatial density of surface festures measured, basin-sized features can be resolved. In particular, the far-side craters Fabry, Riemann, and Szilard comprise a topographically depressed region about 500 km in diameter centered at 120°E and 38.5°N. The floor of this basin is 2.4 to 3.4 km below the reference sphere of 1738.0 km and 4.8 to 5.8 km below the northern rim of the basin. A comparison of the depth of the unfilled basin with the depths of maria-filled front-side basins leads to the conclusion that basalt fill of the near-side maria may be 2 km deep. The topographic map shows good correlation with geologic provinces of young plains and cratered terra in the far-side highland region investigated. Lack of correlation between sampled values of the state-of-the-art 16th-order and 16th-degree harmonic gravity field model and corresponding topographical values leads to the conclusion that the far-side region investigated is isostatically compensated.