On the Polarization Opposition Effect of E-Type Asteroid 64 Angelina

Polarimetric observations of the high-albedo asteroid 64 Angelina were done for the purpose of searching for a polarization opposition effect at phase angles of less than 2.4°. We have found a second inversion angle of about 1.5° and positive polarization of 0.5% at a phase angle of 0.5°. For comparison the polarimetric observations of Comet P/Ashbrook–Jackson are given. Different theoretical approaches to the explanation of this phenomenon are discussed.     

Polarization and brightness opposition effects for the E-type Asteroid 44 Nysa

We present new polarimetric and photometric observations of high-albedo E-type Asteroid 44 Nysa in the BVRI wavebands at phase angles ranging from 0.41° to 7.49° during the 2005 opposition. A bimodal phase-angle dependence of polarization was found for Nysa in the V band. The polarization opposition effect was revealed in the form of a secondary minimum of negative polarization with amplitude ∼0.3% centered at a phase angle ∼0.8°. It is superimposed on the regular negative polarization branch with minimal polarization −0.30% at a phase angle 5.8°. We analyzed all available polarimetric data for E-type Asteroids 44 Nysa, 64 Angelina, and 214 Ashera and confirmed the presence of the polarization opposition effect for high-albedo asteroids at phase angle ∼1° with an amplitude ∼0.35%. The magnitude-phase curves reveal the presence of spike-like opposition effect of brightness for 44 Nysa in the BVRI spectral bands. 44 Nysa is the second high-albedo asteroid after 64 Angelina for which both the polarization opposition effect and the brightness opposition effect are detected. The differences between the parameters of the opposition effects for silicate surfaces (44 Nysa, 64 Angelina, Io) and icy surfaces (Europa, Ganymede, Iapetus, Saturn's rings) are discussed. The specific morphological parameters of opposition effects, in particular the angular width of the polarization opposition effect is comparable to that of the brightness opposition effect, provide almost unequivocal evidence that they are caused by coherent backscattering. One of unexpected results of our investigation is that 44 Nysa becomes bluer with increasing phase angle, while 64 Angelina shows phase reddening.     

Polarization and brightness opposition effects for the E-type Asteroid 64 Angelina

We present new polarimetric and photometric observations of the high-albedo Asteroid 64 Angelina in the UBVRI wavebands at phase angles ranging from 0.43° to 13.02° during oppositions in 1995, 1999, and 2000/2001. The polarization opposition effect has been observed in the form of a sharp peak of negative polarization with amplitude of about −0.4% centered at αmin≈1.8°, which is superimposed on the regular negative polarization branch. The amplitude of the polarization opposition effect appears to be apparition-dependent. Our photometric data confirm the early detected by Harris et al. [1989. Phase relations of high-albedo asteroids: The unusual opposition brightening of 44 Nysa and 64 Angelina. Icarus 81, 365-374] of a very strong and unusually narrow opposition spike, i.e., brightness opposition effect, for Angelina. Thus, 64 Angelina is the first asteroid for which both the polarization opposition effect and the brightness opposition effect have been detected. We observed that the polarization opposition effect as well as the regular negative polarization branch depends on the wavelength of scattered light, but in different manners. In addition, the colors B-V and V-R show little phase-angle dependence, while the color U-B increases with increasing phase angle, thus indicating that the amplitude of the brightness opposition effect is larger in the U band and almost the same in the B, V, and R bands. It appears that all colors indices begin to increase with decreasing phase angle to zero. The composite lightcurve computed with a period of 8.752 h has amplitude of 0.13 magnitude.     

Polarimetry and BVRI photometry of the potentially hazardous near-Earth Asteroid (23187) 2000 PN9

The results of V-band polarimetric observations of the potentially hazardous near-Earth Asteroid (23187) 2000 PN₉ at large phase angles are presented as well as its photometric observations in BVRI bands. Observations were made in March-April 2006 during its close approach to the Earth using the 1.82-m Asiago telescope (Italy) and the 0.7-m telescope at the Chuguevskaya Observational Station (Ukraine). We obtained polarimetric measurements at the phase angle of 115°, the largest phase angle ever observed in asteroid polarimetry. Our data show that the maximum value of the polarization phase curve reached 7.7% and occurred in the phase angle range of 90-115°. The measured values of linear polarization degree, BVRI colors and magnitude-phase dependence correspond to the S-type composition of this asteroid. Based on our observations the following characteristics of the Asteroid (23187) 2000 PN₉ were obtained: a rotation period of 2.5325±0.0004 h, a lightcurve amplitude of 0.13 mag, an albedo of 0.24±0.06 and a diameter of 1.6±0.3 km.     

Observations of Near-Earth Asteroids in Polarized Light

We report the results of position, photometric, and polarimetric observations of two near-Earth asteroids made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. 1.2-hour measurements of the photometric variations of the asteroid 2009 DL46 made onMarch 8, 2016 (approximately 20^m at a distance of about 0.23 AU from the Earth) showed a 0.^m2-amplitude flash with a duration of about 20 minutes. During this time the polarization degree increased from the average level of 2–3% to 14%. The angle of the polarization plane and the phase angle were equal to 113° ± 1° and 43°, respectively. Our result indicates that the surface of the rotating asteroid (the rotation period of about 2.5 hours) must be non-uniformly rough. Observations of another asteroid—1994 UG—whose brightness was of about 17^m and which was located at a geocentric distance of 0.077 AU, were carried out during the night of March 6/7, 2016 in two modes: photometric and spectropolarimetric. According to the results of photometric observations in Johnson’s B-, V-, and R-band filters, over one hour the brightness of the asteroid remained unchanged within the measurement errors (about 0.^m02). Spectropolarimetric observations in the 420–800 nm wavelength interval showed the polarization degree to decrease from 8% in the blue part of the spectrum to 2% in the red part with the phase angle equal to 44?, which is typical for S-type near-Earth asteroids.     

Asteroid polarimetric observations using the Torino UBVRI photopolarimeter

A long-term project of polarimetric observations of minor planets has been carried out since 1995 at the 2.15-m telescope of the El Leoncito Observatory (San Juan, Argentina) using the Torino photopolarimeter. We present here an updated summary of the results, including many measurements obtained during the most recent observing runs. The main purpose of the observations has been to obtain albedo estimates and compare them with previous IRAS radiometric determinations, mainly for objects having small (<50 km) IRAS diameters. Another field of investigation is the measurement of the degree of linear polarization at very small phase angles (less than 1°). The latter observations can be a useful input for modern theoretical models of light scattering from asteroid surfaces. In general, we have obtained a wealth of new results, including objects exhibiting a peculiar polarimetric behavior.     

CCD Polarimetry of Near-Earth Asteroid 2014 JO25 and Comet 41P/Tuttle–Giacobini–Kresák at the Prime Focus of the 2.6-m Shajn Telescope of the Crimean Astrophysical Observatory

The results of the first polarimetric measurements of near-Earth asteroid 2014 JO₂₅ and comet 41P/Tuttle-Giacobini-Kresák performed on April 19, 2017, with a CCD sensor at the prime focus (f/3.85) of the 2.6-m Shajn Telescope of the Crimean Astrophysical Observatory in the R filter are reported. The degree of linear polarization of the asteroid is P = 2.69 ± 0.44% at a phase angle of 55.6°, which is typical of an S-type asteroid. Its geometric albedo is ρ_v ≈ 0.2. A digital filter applied to the direct image of the comet reveals a jet and a tail directed toward the Sun (PA = 45.1°) and away from it (PA = 241.2°), respectively, in the coma. The maximum degree of linear polarization in the near-nucleus region of the comet is 18% at a phase angle of 69.8°. The polarization decreases to 16.2–10.7% in coma regions with a radius of 865–4856 km. Various factors affecting the maximum degree of polarization and the polarization-degree distribution over the coma are discussed.

     

Polarimetry of the Asteroid (599) Luisa: a New Barbarian

Solar System Research - The results of polarimetric observations of the asteroid (599) Luisa carried out on the same type of aperture photoelectric polarimeters of the 2.6-m reflector of the...     

554 Peraga—an asteroid with unusual polarization properties?

This paper presents the results of polarization observations of asteroid 554 Peraga obtained with the UBVRI polarimeter using the 1.25 m telescope of the Crimean Astrophysical Observatory down to phase angles of 3.1°–16.6° from October to November 2006. The asteroid’s polarization phase curve is shown to have a negative branch with the parameters P _min = −1.7% and α_min = 8.4°, which is typical of C-type asteroids. However, these data contradict the results of Zellner and Gradie (1976) obtained in March 1975 that the reflected light from the asteroid’s surface is positively polarized, ≈1% at phase angles of 8°–10°. Since the asteroid’s ecliptic longitudes differ by 160°-145° for the two observation periods, we discuss the possibility that the two sets of observations refer to the asteroid’s two hemispheres with different polarimetric properties.     

Asteroid photometric and polarimetric phase curves: Joint linear‐exponential modeling

Abstract— We present Markov‐Chain Monte‐Carlo methods (MCMC) for the derivation of empirical model parameters for photometric and polarimetric phase curves of asteroids. Here we model the two phase curves jointly at phase angles ≤25° using a linear‐exponential model, accounting for the opposition effect in disk‐integrated brightness and the negative branch in the degree of linear polarization. We apply the MCMC methods to V‐band phase curves of asteroids 419 Aurelia (taxonomic class F), 24 Themis (C), 1 Ceres (G), 20 Massalia (S), 55 Pandora (M), and 64 Angelina (E). We show that the photometric and polarimetric phase curves can be described using a common nonlinear parameter for the angular widths of the opposition effect and negative‐polarization branch, thus supporting the hypothesis of common physical mechanisms being responsible for the phenomena. Furthermore, incorporating polarimetric observations removes the indeterminacy of the opposition effect for 1 Ceres. We unveil a trend in the interrelation between the enhancement factor of the opposition effect and the angular width: the enhancement factor decreases with decreasing angular width. The minimum polarization and the polarimetric slope at the inversion angle show systematic trends when plotted against the angular width and the normalized photometric slope parameter. Our new approach allows improved analyses of possible similarities and differences among asteroidal surfaces.     

Radar observations of the asteroid 2011 UW158

In July 2015 intercontinental bistatic radar observations of the potentially dangerous asteroid 2011 UW158 during its close approach to the Earth were carried out. The asteroid was illuminated at a frequency of 8.4 GHz with the 70-m DSS-14 antenna of the Goldstone Deep Space Communications Complex, while the signal reflected from the asteroid was received with the 32-m radio telescopes of the Quasar VLBI network at the Zelenchukskaya and Badary Observatories. The spectra of the reflected radio signals were obtained. The sizes and rotation period of the asteroid consistent with photometric observations and the ratio of the powers of the reflected signals with left- and right-hand circular polarizations were determined. The derived values suggest that the asteroid has an inhomogeneous surface and a prolate shape. The observations of the Doppler shift of the reflected signal frequency were obtained, which allowed the orbital parameters of the asteroid to be improved.     

Photometric and polarimetric properties of the bruderheim chondritic meteorite

Photometric and polarimetric laboratory measurements were made as a function of phase angle in the U(0.36 μm), G(0.54 μm) and R(0.67 μm) bands for 0°, 30° and 60° incident illumination on four particle size ranges of Bruderheim, an L6 olivine-hypersthene chondritic meteorite. The four particle size ranges were: 0.25–4.76 mm, 0.25–4.76 mm coated with <74 μm powder, 74–250 μm, and <37 μm. In addition, normal reflectance measurements were made in the spectral range from 0.31 to 1.1 μm. Comparison with astronomical data reveals that none of the asteroids in the main belt for which adequate observations exist can be matched with Bruderheim, which is representative of the most common meteoritic material encountered by the Earth. However, it appears from the polarization and photometry data that the surface of the Apollo asteroid Icarus is consistent with an ordinary chondrite composition. This suggests the possibility that this material, although common in Earth-crossing orbits, is rare as a surface constituent in the main asteroid belt.     

Asteroids 1 ceres and 4 vesta: Objects of the Dawn space mission

The Dawn spacecraft of the NASA space mission to asteroids 1 Ceres and 4 Vesta was launched in September 2007. The choice of these two asteroids is deeply grounded: they are the largest and most massive objects of the main belt that are completely different in material composition, evolution history, and internal structure. Recently, the results of observations and numerical modeling have shown their amazing uniqueness: they both have experienced the complex process of thermal evolution and differentiation of their internal mineral resources, but have a completely different internal structure. Being the largest bodies, have they managed to resist the process of collisional evolution in the asteroid belt and have survived in their “primitive form.” Because of this, their study is very important from the point of view of cosmogonic problems regarding the asteroid belt and the Solar System as a whole. The present paper shortly reviews the recent progress in the study of Ceres and Vesta achieved due to observations performed on the Earth (including the polarimetric observations made by the authors) and from the Hubble Space Telescope (HST) before the long-term orbital investigations performed by the Dawn spacecraft.     

Comet C/2002 T7 (LINEAR): Polarimetric and photometric studies

We present the results of polarimetric and photometric observations of dynamically new comet C/2002 T7 (LINEAR) at phase angles from 6° to 26°. During the observations, the comet was at a distance of 2.7–1.3 AU from the Sun and 1.7–2.0 AU from the Earth. The aperture polarimetry was made with the 2.6-m Shain telescope and the 1.25-m AZT-11 telescope of the Crimean Astrophysical Observatory and with the 0.7-m telescope of the Astronomical Institute of the Kharkiv National University during the period from November 21, 2003, to February 21, 2004. The wideband UBVRI and WRC (λ7228/1142 Å) filters and the narrowband GC (λ5260/56 Å) filter were used. The photometric observations of the comet were carried out on February 21, 2004, with narrowband filters isolated the BC (λ4845/65 Å) and RC (λ6840/90 Å) continuum and the C₂ emission (λ5140/90 Å). The phase-angle dependence of linear polarization of the comet has been obtained, and its parameters, such as the minimal polarization P _min = ?1.63%, the phase angle of the minimal polarization α_min = 10.6°, the inversion angle α_inv = 22.7°, and the slope of the phase curve at the inversion angle h = 0.24% per degree, were found. From the photometric observations, the following quantities have been obtained: the column density of molecules C₂ in the line of sight logN (C₂) = ?9.15 mol/cm² and their production rate log Q (C₂) = 27.11 mol/s, the spectral gradient of reflectivity for the dust S′(BC, RC) ≈ 3%/1000 Å, and the dust production parameter Afρ equal to 371 and 273 cm for the blue and red continuum ranges, respectively. According to these results, the physical parameters of comet C/2002 T7 are close to the average characteristics of typical dusty comets.     

Speckle interferometry of asteroids: I. 433 eros

Analytic expressions for the semimajor and semiminor axes and an orientation angle of the ellipse projected by a triaxial ellipsoid (an asteroid) and of the ellipse segment cast by a terminator across the ellipsoid as functions of the dimensions and pole of the body and the asterocenteric position of the Earth and Sun are derived. Applying these formulae to observations of the Earth-approaching asteroid 433 Eros obtained with the speckle interferometry system of Steward Observatory on December 17–18, 1981, and January 17–18, 1982, the following dimensions are derived: (40.5 ± 3.1 km) × (14.5 ± 2.3 km) × (14.1 ± 2.4 km) Eros' north pole is found to lie within 14° of RA = 0^h16^m Dec. = +43° (ecliptic longitude 23°, latitude +37°). Other than knowing the rotation period of Eros, these results are completely independent of any other data, and in the main confirm the results obtained in the 1974–1975 apparition by other methods. These dimensions, together with a lightcurve from December 18, 1981, lead to a geometric albedo of 0.156 ± 0.010. A series of two-dimensional power spectra and autocorrelation functions of the resolved asteroid clearly show it spinning in space.     

Photometric observations of Earth‐impacting asteroid 2008 TC3

Abstract– A calibrated lightcurve is presented of the near‐Earth asteroid 2008 TC₃, obtained before it impacted Earth on October 7, 2008. The asteroid was observed in unfiltered images from the end of astronomical twilight until the object entered Earth’s shadow about 2 h later. The observations covered a wide range of phase angles from 14.79° to 2.93°, during which the asteroid ranged from 82,000 km to 29,000 km distance from the observer. A method is presented for obtaining photometrically filtered brightness values for the asteroid using unfiltered imaging techniques. Over 1,700 images of the asteroid produce a lightcurve with a peak‐to‐peak variation in V of 0.76 magnitude. Analysis of the lightcurve yields values for H = 30.86 ± 0.01 and G = 0.33 ± 0.03. Combined with other constraints on the kinetic energy and diameter of the asteroid, which suggest a low 1.8 g cm^?3 density and albedo 0.05 ± 0.01, the value of H implies an asteroid of about 4.1 m in diameter, 28 m³ in volume, and 51,000 kg in mass. The determined value of G is out of range for normal, larger asteroids of albedo 0.05–0.15.     

Physical investigation of the potentially hazardous Asteroid (144898) 2004 VD17

In this paper we present the observational campaign carried out at ESO NTT and VLT in April and May 2006 to investigate the nature and the structure of the near-Earth object (144898) 2004 VD17. In spite of a great quantity of dynamical information, according to which it will have a close approach with the Earth in the next century, the physical properties of this asteroid are largely unknown. We performed visible and near-infrared photometry and spectroscopy, as well as polarimetric observations. Polarimetric and spectroscopic data allowed us to classify 2004 VD17 as an E-type asteroid. A good agreement was also found with the spectrum of the aubrite meteorite Mayo Belwa. On the basis of the polarimetric albedo (pv=0.45) and of photometric data, we estimated a diameter of about 320 m and a rotational period of about 2 h. The analysis of the results obtained by our complete survey have shown that (144898) 2004 VD17 is a peculiar NEO, since it is close to the breakup limits for fast rotator asteroids, as defined by Pravec and Harris [Pravec, P., Harris, A.W., 2000. Icarus 148, 12-20]. These results suggest that a more robust structure must be expected, as a fractured monolith or a rubble pile in a “strength regime” [Holsapple, K.A., 2002. Speed limits of rubble pile asteroids: Even fast rotators can be rubble piles. In: Workshop on Scientific Requirements for Mitigation of Hazardous Comets and Asteroids, Washington, September, 2002].     

Astrometric and photometric studies of the 2009 WZ104 asteroid as it approached the earth

The astrometric and photometric observations of the potentially hazardous 2009 WZ104 asteroid were carried out at the MTM-500M and ZA-320M automatic telescopes of the Pulkovo Observatory in December 2009. A total of 686 observations were performed in the integral band and 146 observations with B, V, R, and I filters on an arc of the orbit of 17°; these accounted for about 77% of all worldwide observations (). On the basis of the obtained data, the orbit was improved and an estimation of the physical parameters of the asteroid was made. Estimates of the absolute stellar magnitude of the asteroid, H = (20.52 ± 0.04) ^m , as well as its size and mass, were obtained. The taxonomic class of the 2009 WZ104 asteroid (R or Q) was determined. A frequency analysis of the series of observations was carried out; periodicities in the asteroid’s light variation were revealed using this method.     

Polarimetry of main belt asteroids: Wavelength dependence

New UBVRI polarimetric observations of ten asteroids, including space mission targets 1 Ceres and 21 Lutetia, are presented. These observations were obtained with the 1.25-m telescope of the Crimean Astrophysical Observatory and have been used to study the wavelength dependence of polarization for a sample of asteroids belonging to the M and low albedo classes. A more general analysis including also a larger data set of UBVRI polarimetric observations available in the literature for more than 50 main belt asteroids belonging to different taxonomic classes shows that the variation of the polarization degree Pr as a function of wavelength is generally well described by a linear trend. It typically does not exceed 0.2% in the studied spectral range 0.37-0.83 microns and tends to increase for increasing phase angle. Asteroids belonging to the S and M classes are found to exhibit a deeper negative branch and smaller positive polarization for increasing wavelength (negative sign of the slope of ΔPr/Δλ). Since the objects belonging to these classes are known to exhibit reddish reflectance spectra, the observed wavelength behavior of negative polarization contradicts the well-known inverse correlation of Pmin and albedo. Low albedo asteroids show larger dispersion of spectral slopes, but the overall trend is characterized by a shallower negative branch and a larger positive polarization for increasing wavelength (positive sign of the slope of ΔPr/Δλ). A few exceptions from this general trend are discussed. The observed variety in the wavelength dependence of asteroid polarization seems to be mainly attributed to surface composition.     

Polarimetric and Photometric Phase Effects Observed on Transneptunian Object (29981) 1999 TD10

The Kuiper-Belt Object (29981) 1999 TD₁₀, classified as a Scattered-Disk Object, has been observed at three different phase angles with the ESO 8.2-m VLT and FORS 1 instrument in polarimetric mode in November and December 2003. These observations have been used to compute the Stokes parameter q, which represents the linear polarization degree. We have also used the previously published photometric observations to improve the R-band phase function. The main conclusions are as follows: (i) a negative linear polarization degree decreasing with phase angle α up to, at least, α=3°, (ii) for α=3°, (iii) a possible color effect between the R and V band, the polarization degree being more negative in R. The R-band polarimetric observations can be explained by the coherent-backscattering mechanism and fitted by a two-component Rayleigh-scatterer model for a spherical small body. The rotation period of 15.382±0.001 h published by Mueller et al. (2004, Icarus 171, 506–515) and Choi et al. (2003, Icarus 165, 101–111) is confirmed. The R-band phase curve provides H=8.35±0.02 and G=−0.25±0.022 parameters with the IAU H–G formalism.Based on observations obtained at the Cerro Paranal observatory of the European Southern Observatory (ESO) in Chile.