On the aspect ratio of ’Oumuamua : less elongated shape for irregular surface properties

Allona Vazan; Re’em Sari

doi:10.1093/mnras/staa252

On the aspect ratio of ’Oumuamua : less elongated shape for irregular surface properties

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa252 ◽

2020 ◽

Vol 493 (2) ◽

pp. 1546-1552 ◽

Cited By ~ 2

Author(s):

Allona Vazan ◽

Re’em Sari

Keyword(s):

Aspect Ratio ◽

Light Curve ◽

Surface Properties ◽

Specular Reflection ◽

Orientation Distribution ◽

Brightness Variation ◽

Spin Axis ◽

Isotopic Spin ◽

Axis Orientation ◽

Surface Reflection

ABSTRACT The large brightness variation in the observed light curve of ’Oumuamua is probably related to its shape, i.e. to the ratio between its longest axis and its shortest axis (aspect ratio). Several approaches found the aspect ratio of ’Oumuamua to be unusually elongated. Moreover, the spin axis orientation has to be almost perpendicular to the observer in order to obtain such an extreme light curve, a configuration which is unlikely. However, interstellar ’Oumuamua may have different surface properties than we know in our Solar system. Therefore, in this work we widen the parameter space for surface properties beyond the asteroid-like models and study its effect on ’Oumuamua’s light curve. We calculate reflection from a rotating ellipsoidal object for four models: Lambertian reflection, specular reflection, single scattering diffusive, and backscatter . We then calculate the probability to obtain a light-curve ratio larger than the observed, as a function of the object’s aspect ratio, assuming an isotopic spin orientation distribution. We find the elongation of ’Oumuamua to be less extreme for the Lambertian and specular reflection models. Consequently, the probability to observe the light-curve ratio of ’Oumuamua given its unknown spin axis orientation is larger for those models. We conclude that different surface reflection properties may suggest alternatives to the extreme shape of ’Oumuamua , relieving the need for complicated formation scenario, extreme albedo variation, or unnatural origin. Although the models suggested here are for ideal ellipsoidal shape and ideal reflection method, the results emphasize the importance of surface properties for the derived aspect ratio.

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Possible Mechanisms for Cometary Outbursts

International Astronomical Union Colloquium ◽

10.1017/s0252921100012732 ◽

1991 ◽

Vol 116 (2) ◽

pp. 825-851 ◽

Cited By ~ 7

Author(s):

David W. Hughes

Keyword(s):

Brightness Variation ◽

Spin Axis ◽

Axis Orientation ◽

General Change ◽

Geocentric Distance ◽

Cometary Coma ◽

Exponential Decrease

Abstract.A cometary outburst is an unexpected flare-up in the brightness of a comet, with the brightness normally increasing by 2 to 3 magnitudes, but on occasion by up to 5. This outburst is superimposed on the general change in brightness that is related to the comet’s heliocentric and geocentric distance, spin phase, spin axis orientation and activity geography. The brightness variation during outbursts usually has an abrupt, eruptive onset followed by a quasi-exponential decrease and lasts for a few tens of days. Several cometary outbursts are accompanied by the expansion of a spherical halo from the brightest point at the centre of the visible cometary coma.

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Perceived Glossiness: Beyond Surface Properties

Color and Imaging Conference ◽

10.2352/issn.2169-2629.2019.27.8 ◽

2019 ◽

Vol 2019 (1) ◽

pp. 37-42

Author(s):

Davit Gigilashvili ◽

Jean-Baptiste Thomas ◽

Marius Pedersen ◽

Jon Yngve Hardeberg

Keyword(s):

Surface Properties ◽

Human Subjects ◽

Surface Geometry ◽

Surface Reflection ◽

Different Color

Gloss is widely accepted as a surface- and illuminationbased property, both by definition and by means of metrology. However, mechanisms of gloss perception are yet to be fully understood. Potential cues generating gloss perception can be a product of phenomena other than surface reflection and can vary from person to person. While human observers are less likely to be capable of inverting optics, they might also fail predicting the origin of the cues. Therefore, we hypothesize that color and translucency could also impact perceived glossiness. In order to validate our hypothesis, we conducted series of psychophysical experiments asking observers to rank objects by their glossiness. The objects had the identical surface geometry and shape but different color and translucency. The experiments have demonstrated that people do not perceive objects with identical surface equally glossy. Human subjects are usually able to rank objects of identical surface by their glossiness. However, the strategy used for ranking varies across the groups of people.

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Spin axis orientation of Ajisai determined from Graz 2kHz SLR data

Advances in Space Research ◽

10.1016/j.asr.2010.03.029 ◽

2010 ◽

Vol 46 (3) ◽

pp. 251-256 ◽

Cited By ~ 19

Author(s):

D. Kucharski ◽

T. Otsubo ◽

G. Kirchner ◽

F. Koidl

Keyword(s):

Spin Axis ◽

Axis Orientation

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An Exact Method to Determine the Chain Axis Orientation Distribution in High Performance Fibers from a Single Inter-Chain Reflection

MRS Proceedings ◽

10.1557/proc-134-485 ◽

1988 ◽

Vol 134 ◽

Author(s):

Ravi F. Saraf ◽

T.J. Watson

Keyword(s):

High Performance ◽

Orientation Distribution ◽

Inversion Method ◽

Computation Method ◽

Axis Orientation ◽

Complete Chain ◽

Orientation Function ◽

Two Samples ◽

Chain Axis ◽

Oriented Polyethylene

ABSTRACTAn exact pole inversion method is used to calculate the complete chain-axis orientation distribution from a single inter-chain reflection. A brief outline of the formulation and computation method is given. This method is demonstrated by comparing the measured chain-axis distribution from a (002) reflection of oriented polyethylene samples, to the calculated distribution from (110) and (200) reflections of the same sample. The error in the Hermans Orientation function is less than 0.5% for the two samples tested.

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Interpretation of heliocentric water production rates of comets

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833959 ◽

2019 ◽

Vol 623 ◽

pp. A120 ◽

Cited By ~ 4

Author(s):

D. Marshall ◽

L. Rezac ◽

P. Hartogh ◽

Y. Zhao ◽

N. Attree

Keyword(s):

Cross Section ◽

Heliocentric Distance ◽

Rotation Axis ◽

Spin Axis ◽

Water Production ◽

Production Rates ◽

Axis Orientation ◽

Nucleus Shape ◽

Basic Parameters ◽

Water Production Rate

Aims. We investigate the influence of three basic factors on water production rate as a function of heliocentric distance: nucleus shape, the spin axis orientation, and the distribution of activity on a comet’s surface. Methods. We used a basic water sublimation model driven by solar insolation to derive total production rates for different nuclei shapes and spin axis orientations using the orbital parameters of 67P/Churyumov-Gerasimenko. We used known shape models derived from prior missions to the Jupiter Family and short period comets. The slopes of production rates versus heliocentric distance were calculated for the different model setups. Results. The standard (homogeneous) outgassing model confirms the well-known result regarding the heliocentric dependence of water production rate that remains invariant for different nuclei shapes as long as the rotation axis is perpendicular to the orbital plane. When the rotation axis is not perpendicular, the nucleus shape becomes a critically important factor in determining the water production curves as the illuminated cross section of the nucleus changes with heliocentric distance. Shape and obliquity can produce changes in the illuminated cross section of up to 50% over an orbit. In addition, different spin axis orientations for a given shape can dramatically alter the pre- and post-perihelion production curves, as do assumptions about the activity distribution on the surface. If, however, the illuminated cross section of the nucleus is invariant, then the dependence on the above parameters is weak, as demonstrated here with the 67P/Churyumov-Gerasimenko shape. The comets Hartley 2 and Wild 2 are shown to yield significantly different production curve shapes for the same orbit and orientation as 67P/CG, varying by as much as a factor of three as a result of only changing the nucleus shape. Finally, we show that varying just three basic parameters, shape, spin axis orientation, and active spots distribution on the surface can lead to arbitrary deviations from the expected inverse square law dependence of water production rates near 1 au. Conclusions. With the results obtained, we cannot avoid the conclusion that, without prior knowledge of basic parameters (shape, spin axis orientation, activity locations), it is difficult to reveal the nature of cometary outgassing from the heliocentric water production rates. Similarly, the inter-comparison of water production curves of two such comets may not be meaningful.

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Spin rate and spin axis orientation of LARES spectrally determined from Satellite Laser Ranging data

Advances in Space Research ◽

10.1016/j.asr.2012.07.018 ◽

2012 ◽

Vol 50 (11) ◽

pp. 1473-1477 ◽

Cited By ~ 17

Author(s):

D. Kucharski ◽

T. Otsubo ◽

G. Kirchner ◽

G. Bianco

Keyword(s):

Spin Axis ◽

Satellite Laser Ranging ◽

Laser Ranging ◽

Axis Orientation

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Asteroids

Symposium - International Astronomical Union ◽

10.1017/s0074180900151344 ◽

1986 ◽

Vol 118 ◽

pp. 213-221

Author(s):

H. J. Schober

Keyword(s):

Physical Properties ◽

Surface Properties ◽

Spin Axis ◽

Spectral Reflectivity ◽

Topographic Features ◽

Rotation Periods ◽

Magnitude Range ◽

Asteroid Body ◽

Ubv Photometry ◽

Phase Angles

Using a number of different conventional observing methods of astronomy like spectrophotometry, polarimetry, IR-radiometry and UBV-photometry, physical properties of asteroids can be derived, such as diameters, spectral reflectivity and albedo. Based on observable parameters a classification in terms of taxonomic types can be made and the mineralogy of the surface can be determined and compared with meteoritic analogues. UBV-photometry at different phase angles can reveal something about surface properties and diameters, whereas from accurate photometry during different phases of the rotational cycles we are able to derive rotation periods, geometric irregularities of the asteroid-body and topographic features on the surface. If observations of lightcurves are obtained during several oppositions at different ecliptic positions, the orientation of the spin axis in space and sometimes the sense of rotation can be derived. Observations of asteroids are especially well suited to small and medium-sized telescopes, as most of the programmes need long telescope runs. In addition there is a definite need for a large number of observations of asteroids in the magnitude range 12–15 mag.

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SU-8 Processing on a Variety of Substrates

MRS Proceedings ◽

10.1557/proc-605-91 ◽

1999 ◽

Vol 605 ◽

Cited By ~ 3

Author(s):

Yuh-Min Chiang ◽

Mark Bachman ◽

Hung-Pin Chang ◽

Charles Chu ◽

G. P. Li

Keyword(s):

Surface Tension ◽

Aspect Ratio ◽

Surface Properties ◽

Silicon Wafer ◽

Environmental Conditions ◽

High Aspect Ratio ◽

Silicon Substrates

AbstractSU-8 has become a popular material for micromachining high aspect ratio structures. Typically, SU-8 is spun on a polished silicon wafer for processing. After patterning, the SU-8 is used for micromachined structures directly (such as fluidic channels) or as a mold for electroforming. Non-silicon substrates offer the possibility of cheaper processing, improved mold designs, and multi-material devices. Successful SU-8 processing depends strongly on surface properties of the substrate itself as well as environmental conditions during the processing. We explore the issues involved in transferring SU-8 technology to non-silicon substrates such as glass, plastics and metals. Issues such as wettability, adhesion, and surface tension are explored in this study. The findings indicate the merits of non-spinning approaches, such as dipping, spraying, and brushing and point to new SU-8 processes.

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REPLICATION BEHAVIOR FOR MICRO SURFACE FEATURES WITH HIGH ASPECT RATIO AND STRUCTURE DEVELOPMENT IN INJECTION COMPRESSION MOLDING

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512003789 ◽

2012 ◽

Vol 06 ◽

pp. 563-569 ◽

Cited By ~ 8

Author(s):

HAJIME SUZUKI ◽

TETSUO TAKAYAMA ◽

HIROSHI ITO

Keyword(s):

Aspect Ratio ◽

High Aspect Ratio ◽

Molecular Orientation ◽

Orientation Distribution ◽

Compression Molding ◽

Short Delay ◽

Surface Features ◽

Compression Stroke ◽

Short Shot ◽

Injection Compression Molding

Injection compression molding (ICM) with high aspect ratio surface features was performed to clarify the effect of molding conditions on replication characteristics and molecular orientation distribution. Short-shot defects and surface replication were better when using ICM than when using conventional injection molding. A long compression stroke and short delay time condition were optimum conditions to used to achieve uniform surface replication. Molecular orientation was also reduced by the long compression stroke. To reduce molecular orientation, the compression motion should be carried out immediately after injection motion in the case of 0.2 mm thickness. For 0.6 mm thickness, the compression motion was conducted after the shear stress relaxation to reduce the molecular orientation. Short-shot tests revealed distinctive replication behavior in ICM. Results show that replication behavior and local molecular orientation are generated by a slightly frozen layer at the filling area before compression.

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