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1.
New narrow-band (100 Å) photoelectric area-scanning photometry of the Uranus disk is reported. Observations were concentrated on the two strong CH4 bands at λ 6190 and 7300 Å. Adjacent continuum regions at λ 6400 and 7500 Å were also measured for comparison. Both slit and pinhole scans were made in orthogonal directions. Disk structure in each waveband is apparent through lack of circular symmetry in the intensity distribution over the Uranus image. Polar brightening is especially prominent in the λ 7500-Å waveband. Coarse quantitative determinations of the true intensity distribution over the Uranus disk were made. For the λ 6190-Å CH4 band, Uranus exhibits a disk of essentially uniform intensity except for a hint of polar brightening. For the λ 7300-Å CH4 band, moderate limb brightening is apparent. Specifically, the true intensities at the center and limb of the planetary disk are approximately in the proportion 1:2. Extreme limb brightening, with a corresponding intensity ratio greater than 1:4, is not permitted by the observational data.  相似文献   

2.
A photoelectric observation in the near infrared of the 10 February 1977 lunar occultation of Uranus is described and analyzed in terms of planetary radius, limb darkening, and polar brightening. Contact timings, corrected for lunar limb effects, indicate an equatorial radius of 25,700 ± 500km for the visible disk. A modified Minnaert function is used to model limb darkening and polar brightening. Least-squares fits to the observed light curve indicate that Uranus is slightly limb darkened in the passband of the observation (450 ÅA FWHM centered near 6900 ÅA) and that polar brightening is present.  相似文献   

3.
New narrow-band (100 Å) photoelectric slit scan photometry of Uranus has been obtained in the spectral region 6000 to 8500 Å. Coarse radial intensity profiles in seven wavebands are presented. Measurements of the point spread function have been used to partially remove the effects of atmospheric seeing. Restoration of the Uranus image, with a spatial resolution limit ～0″.5 arc, has been achieved by means of analytical Fourier-Bessel inversion. Results of the investigation confirm earlier studies of limb brightening on the Uranus disk. But not all strong CH4 absorption bands are found to exhibit limb brightening. Specifically, the CH4 bands at 8000 and 8500 Å show pronounced apparent limb darkening. Polar brightening may be responsible for the phenomenon. If so, an aerosol haze with a local optical thickness ～0.5 or greater would be required. Visibility of the dense cloud layer located deep in the atmosphere might also cause apparent limb darkening. If so, the maximum permitted [CH4/H2] mixing ratio in the visible atmosphere would correspond to ～3 times the solar value.  相似文献   

4.
The 7 March, 1970 total solar eclipse was observed at wavelengths of 3.2 and 8.3 mm; the object being to use the knife edge of the Moon as it passed across the Sun to improve angular resolution on the Sun. This in turn would provide a radial brightness distribution of the Sun with an angular resolution of a few seconds of arc.Excellent eclipse curves were obtained at 3 mm; however, some external interference marred the 8 mm record near totality.The 8 mm brightness distribution is subject to some uncertainty, but tends to show limb brightening. The 3 mm brightness distribution shows a well defined complex limb brightening within about 1 arc min of the optical limb. The maximum brightening is approximately 30% above the average disc temperature.  相似文献   

5.
We have obtained spectroscopic observations in coronal emission lines by choosing two lines simultaneously, one [Fe x] 6374 Å and the other [Fe xi] 7892 Å or [Fe xiii] 10747 Å or [Fe xiv] 5303 Å. We found that in 95 per cent of the coronal loops observed in 6374 Å, the FWHM of the emission line increases with height above the limb irrespective of the size, shape and orientation of the loop and that in case of 5303 Å line decreases with height in about 89 per cent of the coronal loops. The FWHM of 7892 Å and 10747 Å emission lines show intermediate behavior. The increase in the FWHM of 6374 Å line with height is the steepest among these four lines. We have also studied the intensity ratio and ratio of FWHM of these lines with respect to those of 6374 Å as a function height above the limb. We found that the intensity ratio of 7892 Å and 10747 Å lines with respect to 6374 Å line increases with height and that of 5303 Å to 6374 Å decreases with height above the limb. This implies that temperature in coronal loops will appear to increase with height in the intensity ratio plots of 7892 Å and 6374 Å; and 10747 Å and 6374 Å whereas it will appear to decrease with height in intensity ratio of 5303 Å to 6374 Å lineversus height plot. These findings are up to a height of about 200 arcsec above the limb. The varying ratios with height indicate that relatively hotter and colder plasma in coronal loops interact with each other. Therefore, the observed increase in FWHM with height above the limb of coronal emission lines associated with plasma at about 1 MK may not be due to increase in non-thermal motions caused by coronal waves but due to interaction with the relatively hotter plasma. These findings also do not support the existing coronal loop models, which predict an increase in temperature of the loop with height above the limb.  相似文献   

6.
Narrow-waveband (100 Å) photoelectric slit-scan photometry of the Neptune disk is reported. Observations were concentrated within the strong CH4 band at λ7300 Å. For comparison, measurements were also made within a continuum waveband at λ6800 Å. Point spread function data were obtained in both colors. Qualitative estimates of the true intensity distribution over the Neptune disk were made. Within the λ6800-Å continuum band, Neptune appears as an essentially uniform disk. Within the λ7300 Å CH4 band, the planet exhibits strong limb brightening. Our results appear to require the presence of an optically thin layer of brightly scattering aerosol particles high in the Neptune atmosphere.  相似文献   

7.
Spectropolarimetric observations of a sunspot were carried out with the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife, Spain. Maps of the physical parameters were obtained from an inversion of the Stokes profiles observed in the infrared Fe I line at 15648 Å The regular sunspot consisted of a light bridge which separated the two umbral cores of the same polarity. One of the arms of the light bridge formed an extension of a penumbral filament which comprised weak and highly inclined magnetic fields. In addition, the Stokes V profiles in this filament had an opposite sign as the sunspot and some resembled Stokes Q or U. This penumbral filament terminated abruptly into another at the edge of the sunspot, where the latter was relatively vertical by about 30°. Chromospheric Hα and He II 304 Å filtergrams revealed three superpenumbral fibrils on the limb‐side of the sunspot, in which one fibril extended into the sunspot and was oriented along the highly inclined penumbral counterpart of the light bridge. An intense, elongated brightening was observed along this fibril that was co‐spatial with the intersecting penumbral filaments in the photosphere. Our results suggest that the disruption in the sunspot magnetic field at the location of the light bridge could be the source of reconnection that led to the intense chromospheric brightening and facilitated the supply of cool material in maintaining the overlying superpenumbral fibrils. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
Center-to-limb brightness distribution measurements of the quiet Sun at a wavelength of 3.3 mm show that there is a slight limb brightening at this wavelength. Within the measurement accuracy of the system used, the limb brightening function is only radially dependent. At 3.3 mm, the measurements are consistent with a solar brightness curve that is flat to about r = 0.8 with a rapid increase to a peak value of about 1.3 at the limb. The results show that most of the central disk 3.3-mm emission comes from a thin layer of relatively constant temperature about 1500–3500 km above the photosphere. This work was supported by the U.S. Air Force under Contract No. F04701-69-C-0066.  相似文献   

9.
Shimojo  Masumi  Kurokawa  Hiroki  Yoshimura  Keiji 《Solar physics》2002,206(1):133-142
We present a detailed study of coronal loop brightenings observed in an active region on the solar limb. These brightening loops show expanding and shrinking motions in EUV coronal line images and also show downflow along the loops in Lα and Hα images. By means of time-slice analysis of the images, we found that both the expanding and shrinking motions of the loops are not real motions of plasma but apparent motions like post-flare loops, where the loops at the different height are successively heated and cooled. From a temperature analysis, the time delay between the brightenings of hot 195 Å and cool Lα loops is found to be nearly equal to the time-scale of the conduction cooling. We conclude that these loop brightenings are sources of so called Hα coronal rains.  相似文献   

10.
Cudnik  B.M. 《Solar physics》2004,219(2):197-216
This paper presents the results of a study with images of the Mercury transit of the Sun, 15 November 1999, as observed at the Prairie View Solar Observatory and with three wavelengths of the TRACE satellite. These CCD observations provide an objective source for comparing the optical effects that cause the historic Black Drop under different conditions and with different filters. It appears that a sharp, uniform boundary of sufficient contrast (the solar limb, with the sky beyond the limb being at least as dark as the interior of the Mercurian disk), with a blurring agent, is necessary to produce the effect. Without all these conditions, as in the case of narrow-band Hα at line center or the TRACE UV (1600 Å) and EUV (171 Å), the visibility of the Black Drop is greatly reduced or eliminated, due to the contrast-lowering background of the chromosphere or corona, scattering more light into the umbilicus region.  相似文献   

11.
Previous models of microwave limb brightening have omitted the alignment of spicules along supergranule boundaries, have neglected the high temperature sheath around spicules, and have assumed an interspicular medium which was averaged over chromospheric network and non-network regions. We present a model which includes these factors. By constraining the model to conform to results from earlier UV and optical studies we are effectively left with two free parameters: the temperature at the core of the spicules, T core, and (at solar minimum), the interspicular chromospheric network density model of the lower transition zone. The absence of limb brightening at the short millimeter wavelengths implies T core 6000 k. Differences between the model and certain deconvolved observations near 9 mm are expected as a consequence of an extension of emission beyond the optical limb, predicted by the model, which affects the accuracy of the deconvolution technique. Unlike models which assume homogeneous spicules in a random distribution, ours does not require an abnormally high spicule area.  相似文献   

12.
Orthogonal narrow-band (100 Å) photoelectric slit scan photometry of Uranus has been used to infer the basic two-dimensional structure of the disk within the 7300-Å methane band. Numerical image reconstruction and restoration techniques have been applied to quantitatively estimate the degrees of polar and limb brightening on the planet. Through partial removal of atmospheric smearing, an effective spatial resolution of approximately 0.9 arcsec has been achieved. Peak polar, limb, and central intensities on the disk are in the respective proportions 3:2:1. In addition, the bright polar feature is displaced from the geometric pole towards the equator of the planet.  相似文献   

13.
One of the intrinsic properties of particulate sulfur allotropes is a change in UV-visible reflectivity with temperature change of the material. The surface of Io experiences temperature changes during eclipse which are sufficient to cause a detectable change in the spectral reflectivity of sulfur; thus, if the surface of Io is composed primarily of sulfur allotropes, a change in reflectivity at certain wavelengths should be observable shortly after eclipse reappearance. We observed four eclipse reappearances during July and August of 1983 and saw no posteclipse brightening effects in filter bands selected for sensitivity to color changes in sulfur. Our model of the brightness change for S8 (“yellow” sulfur) implies that this material covers less than 50% of Io's surface. Negative posteclipse brightening observations were also obtained with a filter chosen for the high contrast between SO2 frost and the average albedo of the surface of Io at that wavelength. We conclude that no significant condensation of optically thick SO2 occurred on the surface of Io during these eclipses.  相似文献   

14.
UBV pinhole scans of the Saturn disk have been made with a photoelectric area-scanning photometer. Limb profiles, spaced parallel to the equator, were obtained over the entire southern hemisphere of the planet. Saturn was found to exhibit strong limb brightening in the ultraviolet, moderate limb brightening at blue wavelengths, and strong limb darkening in the visual region of the spectrum. Latitudinal variations in the disk profiles were found. In general, the degree of limb brightening decreases towards the polar region. Pronounced asymmetry is apparent in the disk profiles in each color. The sunward limb is significantly brighter than the opposite limb. This asymmetry depends on phase angle; approaching zero at opposition, it reaches a maximum near quadrature. Our observations are interpreted using an elementary radiative transfer model. The Saturn atmosphere is approximated by a finite homogeneous layer of isotropically scattering particles overlying a Lambert scattering haze or cloud layer. The reflectivity of the haze or clouds is a strongly dependent function of wavelength. Our best-fitting model consists of a clear H2 layer of column density ～31 km-am above the haze or clouds; the maximum permitted H2 column density is ～46 km-am. The H2 column density above the equatorial region appears to be less than at temperate latitudes. The phase-dependent asymmetry in the disk profiles is a natural consequence of the scattering geometry. Our results are consistent with current knowledge of the Saturn atmosphere.  相似文献   

15.
Spectroheliograms were obtained in bands centred at 1.2 mm, 0.8 mm and 0.4 mm wavelength during 1969 and 1971. In order to obtain photometrically valid data, a specialized set of reduction techniques was employed, obviating the effects of severe differential attenuation across the disc by atmospheric water vapour and of emission noise from the atmosphere, before taking out the instrumental spread functions of the telescope and detector.Comparison of our maps with those of other observers at 3 mm and 8.6 mm wavelength suggests that the chromospheric brightness temperature increments above active regions show a monotonic increase with increasing height above the photosphere over the normal increase in brightness temperature in the quiet chromosphere. Within the limit of angular resolution of 3 available, no evidence was recorded of normal limb brightening in our three passbands but the presence of isophotes at 50% of the central disc temperature consistently circumscribing the optical limb implies a narrow spike of sub-millimetre brightening close to the limb.  相似文献   

16.
The spectrophotometric (0.39 < λ < 0.7 λm) properties of three particle-size fractions (diameters <10 λm, <150 λm, and 420–850 λm) of sulfur have been investigated in the laboratory. Particle size, temperature, thermal history, and scattering geometry are all shown to influence the spectral reflectance of the normal (S8) sulfur samples and an “orange-colored” S8 sample produced by quenching molten sulfur. A scattering law consisting of a linear combination of lunar-like and Lambertian terms adequately describes the data for all particle sizes. Where sulfur is darkest (λ < 0.45 λm), the reflectance decreases with increasing particle size, whereas where sulfur is brightest (λ > 0.45 λm) the reflectance increases with decreasing particle size. In reflected light, the long wavelength edge of the strong ultraviolet absorption retreats smoothly to shorter wavelengths with decreasing temperature at ～1.6Å/°K, a value lower than the 2.2Å/°K value previously reported for transmitted light. Near opposition, sulfur powders are found to follow closely a Minnaert limb darkening law except where the reflectance is low, i.e., in the strong ultraviolet absorption band of the larger particle size fractions. It is clear from our data that quantitative comparisons between disk-integrated observations of Io and laboratory measurements of flat samples of sulfur are not adequate unless temperature effects and changes in scattering geometry are included.  相似文献   

17.
Flux variability is one of the defining characteristics of Seyfert galaxies, a class of active galactic nuclei (AGN). Although these variations are observed over a wide range of wavelengths, results on their flux variability characteristics in the ultraviolet (UV) band are very limited. We present here the long-term UV flux variability characteristics of a sample of fourteen Seyfert galaxies using data from the International Ultraviolet Explorer acquired between 1978 and 1995. We found that all the sources showed flux variations with no statistically significant differences in the amplitude of UV flux variation between shorter and longer wavelengths. Also, the flux variations between different near-UV (NUV, \(1850{-}3300\) Å) and far-UV (FUV, \(1150{-}2000\) Å) passbands in the rest frames of the objects are correlated with no time lag. The data show indications of (i) a mild negative correlation of UV variability with bolometric luminosity and (ii) weak positive correlation between UV variability and black hole mass. At FUV, about 50% of the sources show a strong correlation between spectral indices and flux variations with a hardening when brightening behaviour, while for the remaining sources the correlation is moderate. In NUV, the sources do show a harder spectrum when brighter, but the correlation is either weak or moderate.  相似文献   

18.
Using TRACE EUV 171 Å line, Hα line, Zürich radio, RHESSI, and HXRS observations the 29 September 2002 flare (M2.6), which occurred in AR NOAA 0134, was analyzed. Flaring structures were compared with a potential magnetic field model (field lines and quasi-separatrix layers) made from SOHO/MDI full-disk magnetogram. Series of high-resolution SOHO/MDI magnetograms and TRACE white-light images were used to find changes in the active region at the photosphere during the flare. The flare began with a rising of a small dark loop followed by the flare brightening observed in 171 Å with TRACE and Hα lines. In radio wavelengths, first type III bursts were observed 5 min prior to the start of hard X-ray emission, indicating a pre-flare coronal activity. The main hard X-ray emission peak (at 06:36 UT) was associated with the second type III burst activity and several slowly negatively drifting features, all starting from one point on the radio spectrum (probably a shock propagating through structures with different plasma parameters). After this time a huge loop formed and three minutes later it became visible in absorption both in Hα and 171 Å EUV lines. The phase of huge dark loop formation was characterized by long-lasting, slowly negatively drifting pulsations and drifting continuum. Finally, considering this huge loop as a surge an evolution of the event under study is discussed.  相似文献   

19.
M. Podolak  R.E. Danielson 《Icarus》1977,30(3):479-492
The scattering and absorption properties of Axel dust were investigated by means of Mie theory. We find that a flat distribution of particle radii between 0 and 0.1 μm, and an imaginary part of the index of refraction which varies as λ?2.5 produce a good fit to the variation of Titan's geometric albedo with wavelength (λ) provided that τext, the extinction optical depth of Titan's atmosphere at 5000 Å, is about 10. The real part of the complex index is taken to be 2.0. The model assumes that the mixing ratio of Axel dust to gas is uniform above the surface of Titan. The same set of physical properties for Axel dust also produces a good fit to Saturn's albedo if τext = 0.7 at 5000 Å. To match the increase in albedo shortward of 3500 Å, a clear layer (containing about 7 km-am H2) is required above the Axel dust. Such a layer is also required to explain the limb brightening in the ultraviolet. These models can be used to analyze the observed equivalent widths of the visible methane bands. The analysis yields an abundance of the order of 1000 m-am CH4 in Titan's atmosphere. The derived CH4/H2 mixing ratio for Saturn is about 3.5 × 10?3 or an enhancement of about 5 over the solar ratio.  相似文献   

20.
We observed an apparent brightening of Io after eclipse reappearance on June 25, 1971 from Kitt Peak (area scanning at 3500 Å) and Table Mountain (4000 Å) and suggest, in the future, that coordinated observations employ area scanning in the ultraviolet.  相似文献   

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