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1.
P. Maltby 《Solar physics》1972,26(1):76-82
Observations of the penumbral intensity of sunspots in 13 wavelength regions are presented. In 4 wavelength regions 54 sunspots are measured. In the other wavelength regions the number of sunspots considered ranges from 3–19.The penumbral intensity alters with position within the spot. This intensity variation is found to be comparable with the change in intensity from one spot to another. The penumbral intensity is found to be independent of spot size in the sample considered.The penumbra model of Kjeldseth Moe and Maltby (1969) with = 0.055 is supported by the measurements.  相似文献   

2.
Images from three filters of the Voyager 1 wide-angle camera were used to measure the continuum reflectivity and spectral gradient near 6000 Å and the 6190-Å band methane/continuum ratio for a variety of cloud features in Jupiter's atmosphere. The dark “barge” features in the North Equatorial Belt have anomalously strong positive continuum spectral gradients suggesting unique composition, probably not elemental sulfur. Methane absorption was shown at unprecedented spatial scales for the Great Red Spot and its immediate environment, for a dark barge feature in the North Equatorial Belt, and for two hot spot and plume regions in the North Equatorial Belt. Some small-scale features, unresolvable at ground-based resolution, show significant enhancement in methane absorption. Any enhancement in methane absorption is conspicuously absent in both hot spot regions with 5-μm brightness temperature 255°K. Methane absorption and 5-μm emission are correlated in the vicinity of the Great Red Spot but are anticorrelated in one of the plume hot spot regions. Methane absorption and simultaneously maps of 5-μm brightness temperature were quantitatively compared to realistic cloud structure models which include multiple scattering at 5 μm as well as in the visible. A curve in parameter space defines the solution to any observed quantity, ranging from a shallow atmosphere and thin NH3 cloud to a deep atmosphere with a thick ammonia cloud. Without additional constraints, such as center-to-limb information, it is impossible to specify the NH3 cloud optical depth and pressure of a deeper cloud top independently. Variability in H2 quadrupole lines was also investigated and it was found that the constancy of the 4-0 S(1)-line equivalent width is consistent with the constancy of the methane 6190-Å band equivalent width at ground-based resolution, but the much greater variability of the 3-0 S(1) line is inconsistent with either the methane band or 4-0 S(1) line. In hot spot regions the 255°K brightness temperature requires a cloud optical depth of about 2 or less at 5 μm in the NH3 cloud layer. To be consistent with the observed 6190-Å methane absorption in hot spot regions, the NH3 cloud optical depth in the visible is about 7.5, implying that aerosols in hot spot regions have effective radii near 1 μm or less.  相似文献   

3.
The observed relation between the interstellar linear polarization curve parameters K and λ max characterizing the width and the wavelength of the polarization maximum, respectively, is interpreted quantitatively. We have considered 57 stars located in four dark clouds with evidence of star formation: in Taurus, Chamaeleon, around the stars ρ Oph and R CrA. In our modeling we have used the spheroidal dust grain model applied previously to simultaneously interpret the interstellar extinction and polarization curves in a wide wavelength range. The observed trend K ≈ 1.7λ max is shown to be most likely related to the growth of dust grains due to coagulation rather than accretion. The relationship of the interstellar polarization curve parameters K and λ max to the mean dust grain size is discussed.  相似文献   

4.
We present interferometric observations of Saturn and its ring system made at the Hat Creek Radio Astronomy Observatory at a wavelength of 1.30 cm. The data have been analyzed by both model-fitting and aperture synthesis techniques to determine the brightness temperature and optical thickness of the ring system and estimate the amount of planetary limb darkening. We find that the ring optical depth is close to that observed at visible wavelenghts, while the ring brightness temperature is only 7 ± 1°K. These observational constraints require the ring particles to be nearly conservative scatterers at this wavelength. A conservative lower limit to the single-scattering albedo of the particles at 1.30-cm wavelength is 0.95, and if their composition is assumed to be water ice, then this lower limit implies an upper limit of 2.4 m for the radius of a typical ring particle. The aperture synthesis maps show evidence for a small offset in the position of Saturn from that given in the American Ephemeris and Nautical Almanac. The direction and magnitude of this offset are consistent with that found from a similar analysis of 3.71-cm interferometric data which we have previously presented (F.P. Schloerb, D.O. Muhleman, and G.L. Berge, 1979b, Icarus39, 232–250). Limb darkening of the planetary disk has been estimated by solving for the best-fitting disk radius in the models. The best-fitting radius is 0.998 ± 0.004 times the nominal Saturn radius and indicates that the planet is not appreciably limb dark at 1.30 cm. Since our previous 3.71-cm data also indicated that the planet was not strongly limb dark (F.P. Schloerb, D. O. Muhleman, and G.L. Berge, 1979a, Icarus39, 214–230), we feel that the limb darkening is not strongly wavelength dependent between 1.30 and 3.71 cm. The difference between the best-fitting disk radii at 3.71 and 1.30 cm is +0.007 ± 0.007 times the nominal Saturn radius and suggests that the planet is more limb dark at 1.30 cm than at 3.71 cm. Models of the atmosphere which have NH3 as the principal source of microwave opacity predict that the planet will be less limb dark at 1.30 cm. However, the magnitude of the effect predicted by the NH3 models is ?0.009 and only marginally different from the observed value.  相似文献   

5.
The Galileo Probe sampled Jupiter's atmosphere at the edge of a 5-μm hot spot, where it found very little cloud opacity above the 700 mb level. Only τ=1-2 at λ=0.5 μm was inferred from Net Flux Radiometer observations (Sromovsky et al. 1998, J. Geophys. Res.103, 22,929-22,977), in seeming conflict with Chanover et al. (1997, Icarus128, 294-305) who inferred τ=6-8 above the 700 mb level (at λ∼0.9 μm) from 893-nm and 953-nm WFPC2 observations of a group of hot spots. Postulating a heterogeneous cloud structure is one way to resolve the conflict. We obtained a more satisfying resolution by reinterpretation of the HST observations with Probe-compatible assumptions about the vertical distribution of cloud particles. Assuming a physically thin upper (putative NH3) cloud with adjustable optical depth and effective pressure (peff<440 mb) and a physically thin midlevel (putative NH4SH) cloud with adjustable optical depth but a fixed pressure of 1.2 bars, we are able to fit WPFC2 observations with probe-consistent opacities in hot spot regions. With the same cloud pressures, but higher middle cloud opacities, we are even able to fit the visibly bright regions. Little variability is seen in the upper cloud. Best fits to October 1995 WFPC2 observations in dark regions (5-μm hot spots) yielded τupper=1.3-1.9 at 0.9 μm and peff=240 mb−270 mb, while in visibly bright regions between hot spots we obtained τupper=1.6-2.2 and peff=250 mb−290 mb. May 1996 observations yielded slightly higher values of τupper (1.8-2.3 and 2.0-2.8) and peff (250 mb−310 mb and 265 mb−320 mb). We found that the most important variable parameter is the opacity of the middle cloud, which ra nged from τ=1, 2 in dark regions, to τ=8-30 in bright regions. From limb darkening characteristics, we inferred a wavelength-dependent haze opacity ranging from 0.2±0.05 at 660 nm to 0.35±0.05 at 953 nm, and an effective haze pressure near 120 mb. We did not find it necessary to use low single scattering albedos that require effective imaginary indices, that are several orders of magnitude larger than the values of the main putative cloud components.  相似文献   

6.
We have studied the evolution of two dark H filaments as prominences during their disk passage from 12 to 19 February, 1992 and 6 to 17 March, 1992, using Kodaikanal Observatory H and Caii K spectroheliograms. Both the filaments were well outside the spot regions. However, they were connected to sunspots by small threads. Outside the spot regions, the filaments were also anchored between opposite polarity plage regions. Both the filaments were almost straight in the beginning. However, they acquired a curved shape (inverted U-shape) as the spot and plages underwent rotation. It is shown that rotation of the plage and spot plays an important role in the evolution of prominences, one serving as the anchor and the other imparting necessary shear. Once the shear reaches a critical value it starts unwinding the filaments, resulting in the fine structure of the two prominences studied.  相似文献   

7.
Crater morphology and size play a major role in determining whether wind-blown streaks emanating from craters or dark splotches within craters will form. Both bright and dark streaks emanate almost exclusively from bowl-shaped craters. Dark splotches are found mainly in flat-floored craters, especially those that are deep and have high rim relief. Trends of dark splotches in the northern to southern midlatitudes closely follow those of bright streaks, suggesting both were formed by similar winds. In the high southern latitudes, on the other hand, dark splotch trends closely follow those of dark streaks.Qualitative models of streak and splotch formation have been derived from these data and results of Sagan et al. (1972, 1973). Bright streaks probably form by trapping and simultaneous streaming of bright dust downwind. Dark splotched craters in regions with bright streaks usually have upwind bright patches, suggesting these features form by dumping of bright dust over crater rims with some minor redistribution of dark materials toward the downwind sides of craters. Data are consistent with dark streaks forming by erosion or nondeposition of bright material or by trapping of dark material. Dark splotches in these regions are probably mainly the result of trapping of dark sand in the downwind sides of crater floors. Craters with dark splotches and dark streaks are usually rimless and shallow. This is consistent with ponded dark sands easily washing over crater walls and extending downwind.Plots of streak length versus crater diameter suggest a complex history of streak formation for most regions.Bright streak trends and latitudinal distributions are consistent with return flow of dust to the southern hemisphere. Some dark streaks may be direct relics of passing sand and dust storms. Trends of dark streaks and splotches away from the south pole are consistent with the spreading of a debris mantle from the polar regions toward the equator.  相似文献   

8.
Polarimetry is able to show direct evidence for compositional differences in the Venus clouds. We present observations (collected during 212 Venus years by the Pioneer Venus Orbiter) of the polarization in four colors of the bright and dark ultraviolet features. We find that the polarization is significantly different between the bright and dark areas. The data show that the “null” model of L. W. Esposito (1980, J. Geophys. Res.85, 8151–8157) and the “overlying haze” model of J. B. Pollack et al. (1980, J. Geophys. Res.85, 8223–8231) are insufficient. Exact calculations of the polarization, including multiple scattering and vertical inhomogeneity near the Venus cloud tops, are able to match the observations. Our results give a straightforward interpretation of the polarization differences in terms of known constituents of the Venus atmosphere. The submicron haze and uv absorbers are anticorrelated: for haze properties as given by K. Kawabata et al. (1980, J. Geophys. Res.85, 8129–8140) the excess haze depth at 9350 Å over the bright regions is Δτh = 0.03 ± 0.02. The cloud top is slightly lower in the dark features: the extra optical depth at 2700 Å in Rayleigh scattering above the darker areas is ΔτR = 0.010 ± 0.005. This corresponds to a height difference of 1.2 ± 0.6 km at the cloud tops. The calculated polarization which matches our data also explains the relative polarization of bright and dark features observed by Mariner 10. The observed differential polarization cannot be explained by differential distribution of haze, if the haze aerosols have an effective size of 0.49 μm, as determined by K. Kawabata et al. (1982, submitted) for the aerosols overlying the Venus equator. We propose two models for the uv contrasts consistent with our results. In a physical model, the dark uv regions are locations of vertical convergence and horizontal divergence. In a chemical model, we propose that the photochemistry is limited by local variations in water vapor and molecular oxygen. The portions of the atmosphere where these constituents are depleted at the cloud tops are the dark uv features. Strong support for this chemical explanation is the observation that the number of sulfur atoms above the cloud tops is equal over both the bright and dark areas. The mass budget of sulfur at these altitudes is balanced between excess sulfuric acid haze over the bright regions and excess SO2 in the dark regions.  相似文献   

9.
The progressive rotation from the limb onto the disk of a long-lived cluster of coaligned Hα spicules was observed at high spatial resolution on the fringe of a large complex of activity. Although individual spicules were steadily changing, the organized cluster appeared consistently suspended above the photospheric limb when viewed in the wings of Hα (|Δλ| ≈ 0.9 Å). The phenomenon is the counterpart near an active region of the dark band discovered in the quiet low chromosphere by Loughhead (1969). But in the present circumstances the effect is perceived as a weakening of emission, i.e. as a gap rather than an obscuration. The initial gap between the off-band spicules and the photospheric limb narrowed and closed in about 4 h. A day later, the cluster of spicules could be identified at the same wavelength with a cluster of elongated dark mottles, similarly coaligned; they were adjacent to, but not in contact with, a foreshortened patch of faculae. The persistence of the gap in this cluster, and its occurrence in isolated spicules reported here in quiet regions, imply that the phenomenon is an inherent property of spicules. It is proposed that the gap results from a spicule-generating process initiated above the temperature minimum.  相似文献   

10.
Normal albedos of thirteen lunar regions are determined at five wavelengths between 4000 and 8000 Å. The deduced values agree with those of the previous investigators except those given by Gehrelset al. (1964) and Van Diggelen (1965). They increase monotonically with the wavelength. At the shortest wavelength, a slight enhancement is detected for most of the regions observed.  相似文献   

11.
M. R. Kundu 《Solar physics》1972,25(1):108-115
At 3.5 mm wavelength absorption features are observed in correspondence with H dark filaments on the disk; beyond the limb the prominences correspond to emissive regions. The absorption features are larger (2–3 arc) than the corresponding H dark filaments; the emissive regions at the limb have similar angular sizes. The emissive regions at the limb have electron temperatures of 5500±500 K; the amount of absorption observed on the disk leads to mean electron densities of about 5 × 1010 per cm3.  相似文献   

12.
The Mgb1 line profile is studied as a function of spatial position in the sunspot region. Comparing the wavelengths of the core and the wing, in and just outside the penumbra, a reversal in the shift is detected. The displacements of the core and the wing are interpreted as horizontal motions directed into the spot in the chromosphere and as a flow directed out of the spot in deeper layers.Systematic wavelength shifts are detected in the line core in some regions outside the penumbra. This is interpreted as a chromospheric velocity field usually directed horizontally away from the spot.  相似文献   

13.
Joseph Masiero 《Icarus》2010,207(2):795-799
We have investigated the effect of rotation on the polarization of scattered light for the near-Earth asteroid (1943) Anteros using the Dual Beam Imaging Polarimeter on the University of Hawaii’s 2.2 m telescope. Anteros is an L-type asteroid that has not been previously observed polarimetrically. We find weak but significant variations in the polarization of Anteros as a function of rotation, indicating albedo changes across the surface. Specifically, we find that Anteros has a background albedo of pv = 0.18 ± 0.02 with a dark spot of pv < 0.09 covering <2% of the surface.  相似文献   

14.
《Icarus》1986,66(3):403-427
We have determined the Minnaert limb-darkening parameters (B0, k) for three color classes of regions on Io near opposition (solar phase angle = 4–5°). Bright (“white”) areas show k ≈ 0.6 independent of wavelength. k for Average (“orange”) regions starts slightly below 0.5 in the Voyager ultraviolet filter (≈0.35 μm), rises monotonically toward longer wavelengths, and reaches ≈0.6 in the orange (≈0.59 μm), a trend consistent with the globally averaged results of McEwen and Soderblom (NASA Technical Memorandum 86246, pp. 261–262 (1984)). For Polar (“brown”) materials, k lies in the range 0.6–0.7 in all filters longward of ultraviolet. The Bright and Average regions show significantly smaller limb darkening, and smaller wavelength dependence of k, than laboratory samples of sulfur, a discrepancy that might represent the influence of macroscopic surface roughness. From a study of the relative merits of two different techniques for determining limb darkening parameters, we find that the single-image method, involving a single spacecraft image and the choice of a group of “similar” regions, has serious consistency problems when applied to the multicolored surface of Io. In contrast, an adaptation of the two-image solution of McEwen and Soderblom, involving the use of two or more images and computation of the limb darkening for individual surface regions, gives consistent results for spectrally similar regions. We conclude that the two-image technique is the only way to accurately determine the limb darkening of Ionian surface materials.  相似文献   

15.
Interfacial liquid water has been hypothesized to form during the seasonal evolution of the dark dune spots observed in the high latitudes of Mars. In this study we assess the presence, nature and properties of ices - in particular water ice - that occur within these spots using HIRISE and CRISM observations, as well as the LMD Global Climate Model. Our studies focus on Richardson crater (72°S, 179°E) and cover southern spring and summer (LS=175-341°). Three units have been identified of these spots: dark core, gray ring and bright halo. Each unit show characteristic changes as the season progress. In winter, the whole area is covered by CO2 ice with H2O ice contamination. Dark spots form during late winter and early spring. During spring, the dark spots are located in a 10 cm thick depression compared to the surrounding bright ice-rich layer. They are spectrally characterized by weak CO2 ice signatures that probably result from spatial mixing of CO2 ice-rich and ice-free regions within pixels, and from mixing of surface signatures due to aerosols scattering. The bright halo shaped by winds shows stronger CO2 absorptions than the average ice-covered terrain, which is consistent with a formation process involving CO2 re-condensation. According to spectral, morphological and modeling considerations, the gray ring is composed of a thin layer of a few tens of μm of water ice. Two sources/processes could participate to the enrichment of water ice in the gray ring unit: (i) water ice condensation at the surface in early fall (prior to the condensation of a CO2-rich winter layer) or during wintertime (due to cold trapping of the CO2 layer) and (ii) ejection of dust grains surrounded by water ice by the geyser activity responsible for the dark spot. In any case, water ice remains longer in the gray ring unit after the complete sublimation of the CO2. Finally, we also looked for liquid water in the near-IR CRISM spectra using linear unmixing modeling but found no conclusive evidence for it.  相似文献   

16.
The proposal of pilgrim dark energy is based on the speculation that phantom-like dark energy possesses enough resistive force to preclude the black hole formation in the later universe. We explore this phenomenon by assuming the generalized ghost version of pilgrim dark energy. We find that most of the values of the interacting (ξ 2) as well as pilgrim dark energy (u) parameters push the equation of state parameter towards phantom region. The squared speed of sound shows that this model remains stable in most of the cases of ξ 2 and u. We also develop $\omega_{\varLambda}\mbox{--}\omega'_{\varLambda}$ plane and observe that this model corresponds to thawing as well as freezing regions. Finally, it is shown that the non-interacting and interacting generalized ghost versions of pilgrim dark energy correspond to ΛCDM limit on the statefinder plane.  相似文献   

17.
Active regions on the Sun in the 20th solar cycle are studied with special reference to their association with proton flares based on microwave interferometric observations at Toyokawa Observatory. It has been reconfirmed that the active regions associated with intense S-component emission with a high 3-cm to 8-cm flux ratio are likely to produce proton flares. About one fourth of 259 active regions during the period investigated are found to have definite features in the spatial distribution of polarization at a wavelength of 3 cm. Active regions with one particular type of polarization pattern have a good correlation with the occurrence of proton flares.  相似文献   

18.
《Icarus》1986,68(2):313-343
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19.
The model of a young star with a protoplanetary disk and a low-mass companion (q ≤ 0.1) moving in a circular orbit inclined to the disk plane is considered. Hydrodynamic models of such a system have been calculated by the SPH method. The perturbations in the disk caused by the orbital motion of the companion are shown to lead to a strong dependence of the disk illumination conditions on azimuth (because of extinction variations between the star and the disk surface) and, as a result, to the appearance of a large-scale asymmetry in the disk images. Calculations show that the dependence of the disk illumination on azimuth is stronger in the central part of the disk than on the periphery. The bright and dark (shadow) regions are located asymmetrically relative to the line of nodes. The sizes of these regions and their positions on the disk depend on model parameters and orbital phase. During the orbital motion, the bright and dark regions do not follow the companion but execute small-amplitude oscillations relative to some direction. The model properties described above open up new possibilities for detecting low-mass companions in the vicinity of young stars. Stars with protoplanetary disks seen face-on or at low inclinations i are best suited for this purpose.  相似文献   

20.
We present the collection of all the mid- and far-IR observations (λ=3–170 μm) of the young eruptive variable PV Cep available so far in the literature. These data allow us to confirm that flux variability is a prominent feature at mid-IR wavelength (λ=3–25 μm). Color-magnitude plots clearly indicate that the observed variability is not extinction-driven, but mainly influenced by fluctuations of the mass accretion rate. We interpret such variability as due to a hot spot created onto the stellar surface by the column of accreting matter, which heats the inner parts of the disk and determines the observed increase of the near- mid-IR luminosity. A quantitative characterization is given for both the spot itself and the additional thermal component created by it. Far-IR data (λ=60–170 μm) are consistent with the presence of a temperature stratification in a massive and quite un-evolved circumstellar disk.  相似文献   

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