共查询到20条相似文献，搜索用时 31 毫秒
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Voyager full-disk images of Io, available at solar phase angle of α = 2?29° and 101?159°, allow comparisons of the satellite's near-opposition photometric behavior with Earth-based results and the determination of the phase curve out to very high phase angles. The near-opposition data were reduced iteratively for self-consistent phase and rotation curves in each Voyager filter; the resulting phase coefficients, geometric albedos, and rotational lightcurves are consistent with Earth-based findings, except for a previously noted tendency for Voyager to yield somewhat redder spectral information. The derived near-opposition phase coefficients, ranging between 0.016 and 0.024 mag/ deg, decrease with increasing wavelength, a trend weakly noted in some Earth-based observations. The full, α = 2?159° phase curves allow the first direct determination of the phase integral of Io at several wavelengths: q rises from ≈0.7 in the ultraviolet to ≈0.8 in the orange. Combination of the Voyager phase integrals with Earth-based albedo information leads to a best estimate of the bolometric Bond albedo of 0.50 ± 0.10, a value consistent with, but slightly below, previous estimates. 相似文献
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V.G. Shevchenko I.N. Belskaya I.G. Slyusarev Yu.N. Krugly V.G. Chiorny N.M. Gaftonyuk Z. Donchev V. Ivanova M.A. Ibrahimov Sh.A. Ehgamberdiev I.E. Molotov 《Icarus》2012,217(1):202-208
CCD-photometry of three Jupiter Trojan asteroids were carried out to study their opposition effect. We obtained well-sampled magnitude–phase curves for (588) Achilles, (884) Priamus, and (1143) Odysseus in the maximal attainable phase angle range down to 0.1–0.2°. The magnitude–phase relations have a linear behavior in all observed range of phase angles and do not show any non-linear opposition brightening. We have not found any confident differences between phase slopes measured in B, V and R bands. The values of the measured phase slopes of Trojans are different from available data for Centaurs. They are within the range of phase slopes measured for some low-albedo main belt asteroids, also exhibit a linear behavior down to small phase angles. An absence of non-linear opposition brightening puts constraints on the surface properties of the studied objects, assuming very dark surfaces where single scattering plays dominating role.We also determined the rotation periods, amplitudes, the values of color indexes B–V and V–R, and the absolute magnitudes of these asteroids. 相似文献
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Anthony Mallama 《Icarus》2009,204(1):11-499
The empirically derived phase curves of terrestrial planets strongly distinguish between airless Mercury, cloud-covered Venus, and the intermediate case of Mars. The function for Mercury is steeply peaked near phase angle zero due to powerful backscattering from its surface, while that for Venus has 100 times less contrast and exhibits a brightness excess near 170° due to Mie scattering from droplets in the atmosphere. The phase curve of Mars falls between those of Mercury and Venus, and there are variations in luminosity due to the planet’s rotation, seasons, and atmospheric states. The phase function and geometric albedo of the Earth are estimated from published albedos values. The curves for Mercury, Venus and Mars are compared to that of the Earth as well as theoretical phase functions for giant planets. The parameters of these different phase functions can be used to characterize exoplanets. 相似文献
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GPS接收机天线相位中心偏差的检测 总被引：5，自引：0，他引：5
GPS接收机天线相位中心偏差是指GPS天线接收卫星信号的电气中心与基机械几何中心之差。在高精度测量中，这是不容忽视的。讨论了采用基线测量相对测定法确定天线相位中心在水平和垂直方向上的偏差的原理和方法，并给出了测量结果及建议。 相似文献
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A loop flare that occurred on 22 April 1993 near the disk center is examined using the Yohkoh Hard X-ray Telescope (HXT). We specifically looked into the faint early phase of the flare prior to the start of the strong impulsive phase. The pre-impulsive phase, though weak in intensity, is expected to contain essential clues to the mechanism of loop flares according to the causality principle, but it has not received attention previously, probably due to the insufficient dynamic range and cadence of observations by the instruments on earlier satellites. Observations with Yohkoh/HXT can clarify what occurs in this phase. This flare, like many other flares of this type, shows a relatively weak emission with a smooth and gradual increase during this pre-impulsive phase, followed by impulsive bursts, and then turns into a smooth decay phase without impulsive bursts. First, we found that the spectrum for the initial smooth rise part is consistent with a thin-thermal source at a temperature around 80 MK. Imaging of this phase in the HXT/L and M bands shows a single source between the footpoint sources that will come up in the impulsive phase following this phase, suggesting that this hyperhot source is located at a high part of the loop between the footpoints, since this flare takes a form of a loop. Furthermore, as we go up to the earliest times of the flare before this `hyperhot' source phase, two fainter sources are found near the footpoint sources that will appear later in the impulsive phase. The spectra of these sources at this earliest time of the flare, in contrast to the `hyperhot' source, cannot be determined from the HXT because the instrument was not in flare mode, and HXT/M1, M2, and H-band data are, unfortunately, not available at this very initial time. We can guess, however, that they are also of thermal character because the time profile is smooth without any spikes just as in the following `hyperhot' thermal phase, and in the post-impulsive `superhot' thermal phase coming up much later. These findings suggest that there is an important, and probably dynamic, early phase in loop flares that has been unnoticed in the still dark pre-impulsive phase, because the very early footpoint sources change into the loop top source in a matter of 20–30 s, comparable to the dynamic Alfvén time scale. Some implications of our new findings are discussed. 相似文献
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Sunspot activity is usually described by either sunspot numbers or sunspot areas. The smoothed monthly mean sunspot numbers
(SNs) and the smoothed monthly mean areas (SAs) in the time interval from November 1874 to September 2007 are used to analyze
their phase synchronization. Both the linear method (fast Fourier transform) and some nonlinear approaches (continuous wavelet
transform, cross-wavelet transform, wavelet coherence, cross-recurrence plot, and line of synchronization) are utilized to
show the phase relation between the two series. There is a high level of phase synchronization between SNs and SAs, but the
phase synchronization is detected only in their low-frequency components, corresponding to time scales of about 7 to 12 years.
Their high-frequency components show a noisy behavior with strong phase mixing. Coherent phase variables should exist only
for a frequency band with periodicities around the dominating 11-year cycle for SNs and SAs. There are some small phase differences
between them. SNs lag SAs during most of the considered time interval, and they are in general more asynchronous around the
minimum and maximum times of a cycle than at the ascending and descending phases. 相似文献
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A method for interpretation of asteroid phase curves, based on empirical modeling and laboratory measurements, is outlined and preliminary results are presented. A linear-exponential function is used to describe the opposition peaks and negative polarization surges of various asteroids and laboratory samples and a statistical algorithm is used in parameter estimation. The linear-exponential function describes well the phase curves, but dense phase angle coverage, particularly at small phase angles must be obtained to improve the results. Major emphasis should also be put on laboratory study: with an extensive library of laboratory measurements, a stronger connection between the phase curve properties and surface characteristics is possible. 相似文献
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This paper aimed at studying the polarization characteristics of Mercury-like exoplanets via the polarimetric phase curve of the unresolvable Mercury. We utilized the Bayesian non-linear ?tting method to get the photo- metric phase curve and the polarimetric phase curve of Mercury. From these two kinds of curves, we obtained further the polarimetric phase curve of the unresolvable Mercury. The results derived from this curve are as follows: ?rst, in the visible light waveband the order of magnitude of the polarization degree is 10−12; second, the maximum degree of polarization parallel to the scattering plane is comparable to that vertical to the scattering plane, but their corre- sponding phase angles have changed evidently in comparison with the case of the resolvable Mercury; third, when the phase angle is greater than 158°, the polarization degree of the unresolvable Mercury is almost reduced to zero. 相似文献
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The three-dimensional distribution of change in phase travel time of an active region below the solar surface can be constructed
with the technique of acoustic imaging. The interpretation of the distribution of measured phase travel time perturbation
suffers from the finite spatial resolution of the acoustic lenses. In the ray approximation, the phase travel time perturbation
measured in acoustic imaging can be expressed as an integral of the product of the relative sound-speed perturbation and a
kernel. Forward computations show that the vertical resolution of phase travel time perturbation is poor even in the ray approximation.
In this study, we discuss the inversion of phase travel time perturbations to estimate the relative sound-speed perturbation
with a regularized least-squares inversion method. The tests with model perturbations of sound speed show that the inversion
reasonably recovers the distribution of the model perturbation. We also apply the inversion method to the measured phase travel
time perturbation of active region NOAA 7981. 相似文献
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Spectral reflectivities ?(λ) of the features on the disk of Jupiter (NTrZ, NEB, EZ, SEB, STrZ) and the center of the disk of Saturn were measured for different phase angles. The phase dependence of ?(λ) is shown to correspond to the shape of the phase function. 相似文献
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Megan E. Elwood Madden David A. Kring Robert J. Bodnar 《Meteoritics & planetary science》2006,41(2):247-262
Abstract— This study examines the effects of shock metamorphism on fluid inclusions in crystalline basement target rocks from the Ries crater, Germany. The occurrence of two‐phase fluid inclusions decreases from shock stage 0 to shock stage 1, while single‐phase inclusions increase, likely as a result of re‐equilibration. In shock stages 2 and 3, both two‐phase and single‐phase inclusions decrease with increasing shock stage, indicating that fluid inclusion vesicles are destroyed due to plastic deformation and phase changes in the host minerals. However, quartz clasts entrained in shock stage 4 melts contain both single‐phase and two‐phase inclusions, demonstrating the rapid quenching of the melt and the heterogeneous nature of impact deformation. Inclusions in naturally shocked polycrystalline samples survive at higher shock pressures than those in single crystal shock experiments. However, fluid inclusions in both experimental and natural samples follow a similar trend in re‐equilibration at low to moderate shock pressures leading to destruction of inclusion vesicles in higher shock stages. This suggests that shock processing may lead to the destruction of fluid inclusions in many planetary materials and likely contributed to shock devolatilization of early planetesimals. 相似文献
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The work compiles a correlated study of a gravitational quasi equilibrium thermodynamic approach for establishing and signifying a unique behavior of the cosmological entropy and phase transitions in an expanding Universe. On the basis of prescribed boundary conditions for the cluster temperature a relation for the intra‐cluster medium (ICM) of galaxy clusters has been derived. A more productive and signifying approach of the correlation functions used for galaxy clustering phenomena shows a unique behavior of the entropy change where a phenomenon known as the gravitational phase transition occurs. This unique behavior occurs with a symmetry breaking from mild clustering to low clustering and from mild clustering to high clustering which differs from a normal symmetry breaking in material sciences. We also derive results for the specific latent heat associated with the phase transitions of 3.20 Tc and 0.55 Tc for the mildly clustered phase to the low clustered phase and from the mildly clustered phase to the highly clustered phase, respectively. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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It is well known that there is a temporal relationship between coronal mass ejections (CMEs) and associated flares. The duration of the acceleration phase is related to the duration of the rise phase of a flare. We investigate CMEs associated with slow long duration events (LDEs), i.e. flares with the long rising phase. We determined the relationships between flares and CMEs and analyzed the CME kinematics in detail. The parameters of the flares (GOES flux, duration of the rising phase) show strong correlations with the CME parameters (velocity, acceleration during main acceleration phase, and duration of the CME acceleration phase). These correlations confirm the strong relation between slow LDEs and CMEs. We also analyzed the relation between the parameters of the CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a duration of the acceleration phase, and a height of a CME at the end of the acceleration phase. The CMEs associated with the slow LDEs are characterized by high velocity during the propagation phase, with the median equal to 1423 km?s?1. In half of the analyzed cases, the main acceleration was low (a<300 m?s?2), which suggests that the high velocity is caused by the prolonged acceleration phase (the median for the duration of the acceleration phase is equal 90 minutes). The CMEs were accelerated up to several solar radii (with the median ≈?7 R ⊙), which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may potentially precede extremely strong geomagnetic storms. The analysis of slow LDEs and associated CMEs may give important information for developing more accurate space-weather forecasts, especially for extreme events. 相似文献
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The change of source characteristics during the transition from the impulsive phase to the post-burst phase is investigated for cm bursts on a statistical basis. The results are the following: (1) The sudden decrease of the circular polarization degree is found almost invariably at the transition; typically from 20–30% down to a few percent. (2) Some bursts show remarkable source expansions in the post-burst phase. There are no cases in which impulsive bursts have larger source size than the associated post-burst increases. (3) Type III bursts which are indicative of non-thermal phenomena are associated with the impulsive phase but not with the post-burst phase. Implications of these observed results are discussed. 相似文献
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We performed photometry of Cassini Visual Infrared Mapping Spectrometer observations of Iapetus to produce the first phase integrals calculated directly from solar phase curves of Iapetus for the leading hemisphere and to estimate the phase integrals for the trailing hemisphere. We also explored the phase integral dependence on wavelength and geometric albedo. The extreme dichotomy of the brightness of the leading and trailing sides of Iapetus is reflected in their phase integrals. Our phase integrals, which are lower than the results of Morrison et al. (Morrison, D., Jones, T.J., Cruikshank, D.P., Murphy, R.E. [1975]. Icarus 24, 157-171) and Squyres et al. (Squyres, S.W., Buratti, B.J., Veverka, J., Sagan, C. [1984]. Icarus 59, 426-435), have profound implications on the energy balance and volatile transport on this icy satellite. 相似文献
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Zhonglei Gao Hui Zhu Lewei Zhang Qinghua Zhou Chang Yang Fuliang Xiao 《Astrophysics and Space Science》2014,351(2):427-434
Chorus waves have been suggested to be effective in acceleration of radiation belt electrons. Here we perform gyro-averaged test-particle simulations to calculate the bounce-averaged pitch angle and energy diffusion coefficients for parallel-propagating monochromatic chorus waves, and perform a comparison of test-particle (TP) model with quasi-linear (QL) theory to evaluate the influence of nonlinear processes. For small amplitude chorus waves, the diffusion coefficients of TP and QL models are in good agreement. As the wave amplitude reaches a threshold value, two nonlinear processes (phase trapping and phase bunching) start to occur, especially at large equatorial pitch angles. Phase trapping yields rapid increases in pitch angle and kinetic energy. In contrast, phase bunching causes overall decreases in pitch angle and kinetic energy. For the waves with amplitudes slightly above the threshold value, the average behavior is dominated by the phase trapping, and TP diffusion coefficients are larger than QL ones. As wave amplitude increases, TP diffusion coefficients become smaller than QL ones, indicating that phase trapping gradually reduces the dominance over phase bunching. 相似文献
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We develop a three-parameter H, G1, G2 magnitude phase function for asteroids starting from the current two-parameter H, G phase function. We describe stochastic optimization of the basis functions of the magnitude phase function based on a carefully chosen set of asteroid photometric observations covering the principal types of phase dependencies. We then illustrate the magnitude phase function with a chosen set of observations. It is shown that the H, G1, G2 phase function systematically improves fits to the existing data and considerably so, warranting the utilization of three parameters instead of two. With the help of the linear three-parameter phase function, we derive a nonlinear two-parameter H, G12 phase function, and demonstrate its applicability in predicting phase dependencies based on small numbers of observations. 相似文献
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Belskaya Irina N. Barucci Antonella M. Shkuratov Yurij G. 《Earth, Moon, and Planets》2003,92(1-4):201-206
Information on the surface structure of the Kuiper Belt objectscan be obtained from studies of their opposition brightening.Although KBOs are observed at a very limited phase angle rangethey represent a unique opportunity to study the backscatteringphenomenon down almost to zero phase angle. Preliminaryestimations of the opposition effect amplitude and width based oncomposite phase curves of four KBOs and two Centaurs showed theexistence of a very narrow opposition surge of about 0.1–0.2 mag at phase angles less than 0.1–0.2 deg. It may indicate a highporosity of the KBOs regoliths. Further observations are needed toconfirm this phenomenon. 相似文献