Saturn rings: divisions, gaps and ringlets from ground-based telescopes

1984 ◽  
Vol 75 ◽  
pp. 147-154 ◽  
Author(s):  
Audouin Dollfus
Keyword(s):  
Phase Angle ◽  
Volume Density ◽  
Light Curves ◽  
High Magnification ◽  
Density Dependent ◽  
Opposition Effect ◽  
Small Phase ◽  
Saturn's Rings ◽  
Phase Angles ◽  
Zero Phase

ABSTRACTThe high magnification visual telescopic observation of Saturn’s rings exhibits divisions, gaps and bright sub-rings. B. Lyot gave a first description of these features. Later, with still more resolving telescopes, we improved the analysis of the ring features. Some gaps and concentric bright or dark sub-rings are phase angle dependent; the steep luminance peaks of their light curves around zero phase angle are volume-density dependent (opposition effect); the overall result produces changes in the shapes and intensities of these features at small phase angles, which are analysed.

scholarly journals Longitudinal variations, the opposition effect and monochromatic albedos for Mars

1971 ◽  
Vol 40 ◽  
pp. 141-155
Author(s):  
William M. Irvine ◽  
James C. Higdon ◽  
Susan J. Ehrlich
Keyword(s):  
Phase Curve ◽  
Central Meridian ◽  
Opposition Effect ◽  
Small Phase ◽  
Longitudinal Variations ◽  
The Mean ◽  
Phase Angles ◽  
Narrow Bands ◽  
Zero Phase ◽  
Phase Phase

Observations of Mars previously reported in 10 narrow bands between 3150 Å and 1.06 μ and in UBV are analyzed for brightness variations which correlate with longitude of the central meridian. Such an effect is found for λ ≥ 5000 Å, with some evidence for such a correlation at λ = 4570 Å. The data are then corrected to the mean (over longitude) brightness and a linear phase curve fitted to those observations with phase angle i ≥ 15°. An opposition effect (anomalous brightening at small phase angles) is found for wavelengths λ ≤ 5500 Å, in contrast to a result previously reported. The magnitude at zero phase, phase coefficient, and monochromatic albedo are computed for Mars as a function of wavelength.

scholarly journals Phase-curve analysis of comet 67P/Churyumov-Gerasimenko at small phase angles

2019 ◽  
Vol 630 ◽  
pp. A11
Author(s):  
N Masoumzadeh ◽  
L Kolokolova ◽  
C Tubiana ◽  
M. R. El-Maarry ◽  
S Mottola ◽  
...  
Keyword(s):  
Phase Angle ◽  
Textural Properties ◽  
Phase Ratio ◽  
Phase Curve ◽  
Model Parameters ◽  
Study Phase ◽  
Opposition Effect ◽  
Small Phase ◽  
Phase Angles ◽  
Comet 67P

Aims. The Rosetta-OSIRIS images acquired at small phase angles in three wavelengths during the fly-by of the spacecraft on 9–10 April 2016 provided a unique opportunity to study the opposition effect on the surface of comet 67P/Churyumov-Gerasimenko (67P). Our goal is to study phase curves of the nucleus at small phase angles for a variety of surface structures to show the differences in their opposition effect and to determine which surface properties cause the differences. Methods. We used OSIRIS NAC images that cover the Ash-Khepry-Imhotep region to extract the phase curve, that is, the reflectance of the surface as a function of phase angle. We selected six regions of interest (ROIs) and derived the phase curves for each ROI. We fit a linear-exponential function to the phase curves. The resulting model parameters were then interpreted by spectrophotometric, geomorphological, and phase-ratio analyses, and by investigating the influence of structural and textural properties of the surface. Results. We find evidence for the opposition effect (deviation of the phase curve from linear behavior) in phase curves for all areas. We found an anticorrelation between the phase ratio and reflectance in a small phase angle range. This provides evidence for the shadow-hiding effect. We conclude that the decrease in the slope of the phase ratio versus reflectance indicates a decrease in the proportion of shadowed regions and reduces the contribution of the shadow-hiding effect. Large uncertainties in the determination of the opposition effect parameters with respect to wavelength do not allow us to conclusively claim coherent backscattering in the opposition effect phenomenon. Based on the two analyses, we conclude that the opposition effect of comet 67P in the Ash-Khepry-Imhotep region is mainly affected by shadow-hiding.

The multi-wavelength phase curves of minor bodies from the SLOAN Moving Objects Catalog

2021 ◽  
Author(s):  
Alvaro Alvarez-Candal ◽  
Paula Benavidez ◽  
Adriano Campo Bagatin ◽  
Toni Santana-Ros ◽  
Santiago Jimenez Corral
Keyword(s):  
Phase Angle ◽  
Moving Objects ◽  
Sloan Digital Sky Survey ◽  
Filter System ◽  
Sky Survey ◽  
Small Phase ◽  
Multi Wavelength ◽  
Absolute Magnitudes ◽  
Phase Angles ◽  
Zero Phase

<p class="p1"><span class="s1">Phase curves of minor bodies describe their brightness change with phase angle, once distance effects have been removed. Using phase curves it is possible to obtain absolute magnitudes, useful parameters as they can be used as a proxy of sizes, with limitations due to albedo. In particular, in this work, we present phase curves of several thousands of minor objects in the filter system of the SLOAN Digital Sky Survey (SDSS).</span></p> <p class="p1"><span class="s1">We obtained the phase curves using the Moving Object Catalog (MOC) of the SDSS including in the final uncertainties those of the input magnitudes and also the uncertainty due to the likely change in magnitude due to rotational variation of the objects. The final products are the absolute magnitudes H</span><span class="s2"><sub>λ</sub></span><span class="s1"> and G12</span><span class="s2"><sub>λ</sub></span><span class="s1">, where λ indicates any of the five central wavelengths of the SDSS filter system. We computed colors at zero phase angle, or absolute colors, that are not affected by phase effects and could be used as a benchmark for future studies. We also analyze the behavior at small phase angles (<7.5 degrees) where the opposition effect dominates.</span></p>

scholarly journals The contribution of atmospheric aerosols to the Martian opposition effect

1971 ◽  
Vol 40 ◽  
pp. 166-169
Author(s):  
Jaylee M. Mead
Keyword(s):  
Atmospheric Aerosols ◽  
Mie Scattering ◽  
The Other ◽  
Spherical Particles ◽  
Refractive Indices ◽  
Opposition Effect ◽  
Absorbing Materials ◽  
Small Phase ◽  
Ice Water ◽  
Phase Angles

Mie scattering calculations have been made for atmospheric aerosols having various indices of refraction to determine their possible contribution to a Martian opposition effect, such as that reported by O'Leary in 1967. Neither substances with a real index between 1.20 and 1.50, such as ice, water, or solid CO2, nor highly absorbing materials, such as limonite, can produce the observed effect. Submicron-sized spherical particles with refractive indices of 1.55 to 2.00 do, on the other hand, exhibit a marked increase in reflectivity at small phase angles and might be responsible for the enhanced brightness at the shorter wavelengths.

scholarly journals Opposition effect on S-type asteroid (25143) Itokawa

2018 ◽  
Vol 616 ◽  
pp. A178 ◽  
Author(s):  
Mingyeong Lee ◽  
Masateru Ishiguro
Keyword(s):  
Linear Increase ◽  
Clear Correlation ◽  
Slope Parameter ◽  
Sample Return ◽  
Opposition Effect ◽  
Imaging Camera ◽  
Small Phase ◽  
Solar System Bodies ◽  
Sample Return Mission ◽  
Phase Angles

Aims. The opposition effect has been detected on solar system bodies such as asteroids and comets. Two mechanisms have been proposed to explain the effect: the shadow-hiding opposition effect (SHOE) and the coherent backscattering opposition effect (CBOE). The Hayabusa asteroid sample return mission provides a unique opportunity to investigate the opposition effect on disk-resolved images of the S-type asteroid (25413) Itokawa at very small phase angles α. Methods. We made use of the data taken at α = 0.°04–2.°54 using the Asteroid Multi-band Imaging Camera (AMICA) on UT 2005 October 13. Comparing sets of two images taken at different phase angles, we derived the opposition slope parameter (SOE) that characterizes a linear increase in the reflectance I∕F per unit phase angle. Results. We found that (i) SOE is less dependent on the incidence and emission angles; (ii) the reflectance increases nonlinearly toward the opposition at small angles with α ≲ 1.°4, showing a good correlation between mean I∕F and SOE; and (iii) SOE becomes nearly constant at α ≳ 1.°4 and shows no clear correlation between I∕F and SOE. Conclusions. From these results, we conjecture that CBOE is dominant at α ≲ 1.°4, while SHOE is dominant at α ≳ 1.°4.

scholarly journals Ceres’ opposition effect observed by the Dawn framing camera

2018 ◽  
Vol 620 ◽  
pp. A201 ◽  
Author(s):  
Stefan E. Schröder ◽  
Jian-Yang Li ◽  
Marc D. Rayman ◽  
Steven P. Joy ◽  
Carol A. Polanskey ◽  
...  
Keyword(s):  
Wavelength Dependence ◽  
Phase Curve ◽  
Angular Width ◽  
Opposition Effect ◽  
Physically Based ◽  
Phase Angles ◽  
Coherent Backscatter ◽  
Zero Phase ◽  
Geometric Albedo ◽  
Framing Camera

Context. The surface reflectance of planetary regoliths may increase dramatically towards zero phase angle, a phenomenon known as the opposition effect (OE). Two physical processes that are thought to be the dominant contributors to the brightness surge are shadow hiding (SH) and coherent backscatter (CB). The occurrence of shadow hiding in planetary regoliths is self-evident, but it has proved difficult to unambiguously demonstrate CB from remote sensing observations. One prediction of CB theory is the wavelength dependence of the OE angular width. Aims. The Dawn spacecraft observed the OE on the surface of dwarf planet Ceres. We aim to characterize the OE over the resolved surface, including the bright Cerealia Facula, and to find evidence for SH and/or CB. It is presently not clear if the latter can contribute substantially to the OE for surfaces as dark as that of Ceres. Methods. We analyze images of the Dawn framing camera by means of photometric modeling of the phase curve. Results. We find that the OE of most of the investigated surface has very similar characteristics, with an enhancement factor of 1.4 and a full width at half maximum of 3° (“broad OE”). A notable exception are the fresh ejecta of the Azacca crater, which display a very narrow brightness enhancement that is restricted to phase angles <0.5° (“narrow OE”); suggestively, this is in the range in which CB is thought to dominate. We do not find a wavelength dependence for the width of the broad OE, and lack the data to investigate the dependence for the narrow OE. The prediction of a wavelength-dependent CB width is rather ambiguous, and we suggest that dedicated modeling of the Dawn observations with a physically based theory is necessary to better understand the Ceres OE. The zero-phase observations allow us to determine Ceres’ visible geometric albedo as pV = 0.094 ± 0.005. A comparison with other asteroids suggests that Ceres’ broad OE is typical for an asteroid of its spectral type, with characteristics that are primarily linked to surface albedo. Conclusions. Our analysis suggests that CB may occur on the dark surface of Ceres in a highly localized fashion. While the results are inconclusive, they provide a piece to the puzzle that is the OE of planetary surfaces.

scholarly journals Nature of Dust Grains in the Atmosphere of Comet Ashbrook

1980 ◽  
Vol 90 ◽  
pp. 259-262 ◽  
Author(s):  
O. V. Dobrovolsky ◽  
N. N. Kiselev ◽  
G. P. Chernova ◽  
F. A. Tupieva ◽  
N. V. Narizhnaja
Keyword(s):  
Dust Grains ◽  
Opposition Effect ◽  
Small Phase ◽  
Phase Angles ◽  
Anomalous Polarization

Anomalous polarization at small phase angles is confirmed as a common feature of dusty cometary atmospheres. The opposition effect is detected and interpreted as evidence of similarity between grains covering interplanetary, cometary and asteroidal surfaces. The prevailing radii of dust grains in the comet's atmosphere are estimated to be 0.15-0.19 μm.

Multi-wavelength phase curves of minor bodies

2020 ◽  
Author(s):  
Alvaro Alvarez-Candal ◽  
Adriano Campo Bagatin ◽  
Paula Benavidez ◽  
Toni Santana-Ros
Keyword(s):  
Power Spectrum ◽  
Phase Angle ◽  
Absolute Magnitude ◽  
Resolving Power ◽  
Multiple Wavelength ◽  
Multi Wavelength ◽  
Using Data ◽  
A Minor ◽  
Phase Angles ◽  
Zero Phase

&lt;p&gt;The brightness of minor bodies depends, among other things, on their phase curves. Furthermore, the absolute magnitude, of a minor body is obtained from these curves, requiring observations at different phase angles, thus being impossible to obtain in a single observing night. Large photometric surveys help due to serendipitous observations of minor bodies in different epochs and phase angles.&lt;/p&gt; &lt;p&gt;Multiple wavelength phase curves have not been thoroughly explored yet, in particular, the possibility of obtaining photo-spectra (a very low resolving-power spectrum) at zero phase angle, i.e., not affected by phase coloring. In this presentation, we show preliminary results of multi-wavelength phase curves for over a thousand objects obtained using data from the SLOAN moving object catalog and discuss the statistical properties of the sample.&lt;/p&gt;

The Eclipsing Binary WX Eridani

1979 ◽  
Vol 46 ◽  
pp. 385
Author(s):  
M.B.K. Sarma ◽  
K.D. Abhankar
Keyword(s):  
Light Curve ◽  
Spectral Type ◽  
Orbital Period ◽  
Primary Component ◽  
Light Curves ◽  
Absorption Feature ◽  
Primary Star ◽  
Eclipsing Binary ◽  
The Times ◽  
Phase Angles

AbstractThe Algol-type eclipsing binary WX Eridani was observed on 21 nights on the 48-inch telescope of the Japal-Rangapur Observatory during 1973-75 in B and V colours. An improved period of P = 0.82327038 days was obtained from the analysis of the times of five primary minima. An absorption feature between phase angles 50-80, 100-130, 230-260 and 280-310 was present in the light curves. The analysis of the light curves indicated the eclipses to be grazing with primary to be transit and secondary, an occultation. Elements derived from the solution of the light curve using Russel-Merrill method are given. From comparison of the fractional radii with Roche lobes, it is concluded that none of the components have filled their respective lobes but the primary star seems to be evolving. The spectral type of the primary component was estimated to be F3 and is found to be pulsating with two periods equal to one-fifth and one-sixth of the orbital period.

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