Aggregate dust model to study the polarization properties of comet C/1996 B2 Hyakutake

The observed linear polarization data of comet Hyakutake are studied at wavelengths λ=0.365 μm,λ=0.485 μm and 0.684 μm through simulations using Ballistic Particle-Cluster Aggregate and Ballistic Cluster-Cluster Aggregate aggregates of 128 spherical monomers.We first found that the size parameter of the monomer,x～1.56-1.70,turned out to be the most suitable which provides the best fits to the observed dust scattering properties at three wavelengths:λ=0.365 μm,0.485 μm and 0.684 μm.Thus,the effective radius of the aggregate(r)lies in the range 0.45 μm ≤ r≤ 0.49 μm at λ=0.365 μm;0.60μm < r < 0.66 μm at λ=0.485 μmand 0.88 μm < r < 0.94 μm at λ=0.684 μm.Now using superposition T-MATRIX code and the power-law size distribution,n(r)～r-3,the best-fitting values of complex refractive indices are calculated for the observed polarization data at the above three wavelengths.The best-fitting complex refractive indices(n,k)are found to be (1.745,0.095)at λ=0.365 μm,(1.743,0.100)at λ=0.485 μm and(1.695,0.100)at λ=0.684 μm.The refractive indices derived from the present analysis correspond to a mixture of both silicates and organics,which are in good agreement with the in situ measurement of comets by different spacecraft.     

Nitrogen Sulfide In Comets Hyakutake (C/1996 B2) And Hale–Bopp (C/1995 O1)

The chemistry of both nitrogen and sulfur presents interesting problems in comets.In this paper, we use a model of cometary comae with gas-phase chemical kineticsand gas dynamics to predict molecular abundances in the inner coma region for twoof the brightest comets in the past 20 years, Hyakutake (C/1996 B2) and Hale–Bopp(C/1995 O1). In this progress report we concentrate on the gas-phase chemistry of thenitrogen sulfide (NS) radical at a heliocentric distance of 1 AU to study the abundanceof NS using a detailed photo and chemical reaction network with over 100 species andabout 1000 reactions. The results are compared with recent observations of CometHale–Bopp and reveal that conventional gas-phase reactions schemes do not produceNS in sufficient quantities to explain the observations. We plan to continue therefinement of the model to improve agreement with observational constraints.     

Comet Hyakutake (C/1996 B2): Spectacular disconnection event and the latitudinal structure of the solar wind

Images of comet Hyakutake (C/1996 B2) are analyzed in conjunction with solar wind data from spacecraft to determine the relationship between solar wind conditions and plasma tail morphology. The disconnection event (DE) on March 25, 1996 is analyzed with the aid of data from the IMP-8 and WIND Earth-orbiting spacecraft and the DE is found to be correlated with a crossing of the heliospheric current sheet. The comet was within of Earth at the time of the DE and data from IMP-8 and WIND show no high-speed streams, significant density enhancements or shocks.The latitudinal variation in the appearance and orientation of the plasma tail are interpreted based on results from the Ulysses spacecraft. In the polar solar wind region, the comet has a relatively undisturbed appearance, no DEs were observed, and the orientation of the plasma tail was consistent with a higher solar wind speed. In the equatorial solar wind region, the comet's plasma tail had a disturbed appearance, a major DE was observed, and the orientation of the plasma tail was consistent with a lower solar wind speed. The boundary between the equatorial and polar regions crossed by comet Hyakutake in April 1996 was near 30°N (ecliptic) or 24°N (solar) latitude.     

The rotational structure of the B-X system of sulfur dimers in the spectra of Comet Hyakutake (C/1996 B2)

We have constructed line-by-line fluorescence models for the ro-vibrational bands of the B-X system of sulfur dimers (S₂). For the first time the detailed rotational lines of the bands are clearly resolved in the high-resolution echelle spectra of Comet Hyakutake (C/1996 B2), which were obtained at the Kitt Peak 4-m telescope on 26.4 March 1996 (UT). In order to construct satisfactory band models of the B-X system, we first compared the models to laboratory spectra available in literature, and then compared the models including Swings effects to the high-resolution spectra of Hyakutake. From the model fits, we derived a rotational temperature of 70±10 K, which should represent a temperature of a coma region close to the nucleus, where most of the S₂ emissions originate. We present previously proposed scenarios for the origin of S₂ in cometary comae, and compare them with our spectral analysis.     

THE FRAGMENTS OF COMET HYAKUTAKE (C/1996 B2)

Several fragments of Comet Hyakutake were observed in March and April of 1996. This leads to the impression that the splitting of Comet Hyakutake on a small scale occurred frequently. Data analysis points to a rotation period of about 6.18hr if the fragments of Apr. 11 are the condensations within a jet.     

Striated features in the dust tail of comet C/2006 P1 (McNaught)

To explain the distinct transversal striae observed in the tail of comet C/2006 P1 (McNaught) near the perihelion, a dynamic model for the formation of the dust tail of the comet has been developed. It is supposed that, on the surface of the nucleus, there are three local active domains of the increased outflow of the material. Formation of the striated features is caused by different rates of material outflow from the active areas depending on which side of the rotating nucleus, illuminated or shadowed, these areas are located. It has been found that the period of the axial rotation of the comet is 21 h.     

Analyses of dust coma morphology of Comet Hyakutake (1996 B2) near perigee: outburst behavior, jet motion, source region locations, and nucleus pole orientation

We present inner-coma dust imaging of Comet Hyakutake (1996 B2) obtained on 11 consecutive nights in late March 1996, an interval including a major outburst and the comet’s closest approach to Earth. The evolution of the outburst morphology is followed, along with the motion along the tail of several outburst fragments. Two spiral dust jets—a primary jet, along with a much weaker secondary jet—are visible throughout the interval and are produced by two source regions on a rotating nucleus. These are examined as a function of rotational phase and viewing geometry, with their appearance changing from a nearly face-on view on March 18 to side-on by March 28. The dust outflow velocity as a function of distance from the nucleus is derived, with the dust continuing to accelerate to a distance of 4000 km or more and reaching an average outflow velocity of 0.38 km s⁻¹ between 3000 and 8000 km. We present details of our Monte Carlo modeling of the jets and our methodology of fitting the model to the images. The modeling yields the pole orientation of the nucleus, with an obliquity of approximately 108°, corresponding to an RA of 13^h41^m and a Dec of −1.1°. For an assumed spherical nucleus, the primary active region is centered at approximately −66° latitude, has a radius of about 56°, and therefore covers about 22% of the surface. The source of the secondary jet is at a latitude of −28°, has a radius of about 16°, and is located at a longitude nearly 180° away from the primary source. Estimated uncertainties for the pole orientation and the source locations and sizes are each about 3°. This solution for the nucleus orientation and source locations explains the strong asymmetry in measured production rates before and after perihelion in radio observations (Biver et al., 1999, Astron. J. 118, 1850-1872). The modeling also tightly constrains the sidereal rotation period as 0.2618 ± 0.0001 day, completely consistent with the expected +0.0003 day difference from the observed solar rotation period of 0.2614 ± 0.0004 day determined by Schleicher and Osip (2002, Icarus 159, 210-233), given the pole orientation and position of the comet in its orbit.     

Temporal deconvolution of the hydrogen coma: II. Pre- and post-perihelion activity of Comet Hyakutake (1996 B2)

Comet 1996 B2 (Hyakutake) displayed strong evidence for break-up, with a prominent antisunward dust spike and fragments traveling antisunward for many days after an eruptive event in late March 1996. Because of its high orbital inclination and rapid southward motion after perihelion, its post-perihelion activity was not well monitored from the ground. The SWAN all-sky Lyman-alpha camera on the SOHO spacecraft was ideally placed for long-term monitoring of the hydrogen coma of Comet Hyakutake both before and after perihelion. The SWAN images were analyzed with a new time-resolved model (TRM) that provides daily averages of the water production rate and an estimate of the hydrogen atom lifetime (dominated by charge exchange with solar wind protons) during extended periods throughout the apparition. A long-term variation of water production rate of , where r is the heliocentric distance in AU was found. The daily average values of the production rate covered the March 19 outburst and two more outbursts seen in the April before perihelion, which had progressively shorter durations at respectively smaller heliocentric distances. The long-term variation of the production rate was found to be consistent with the seasonal effect predicted by the jet rotation model of Schleicher and Woodney [2003. Analyses of dust coma morphology of Comet Hyakutake (1996 B2) near perigee: Outburst behavior, jet motion, source region locations, and the nucleus pole orientation. Icarus 162, 190-213] when added to a more steady source that is about two-thirds of the maximum of the jet source. The seasonal effect in their model found the dust jet source largely not illuminated after perihelion, coinciding with somewhat reduced overall activity and the absence of outbursts and fragmentation. The locations of the dust jets appear to be responsible for the outbursts and fragmentation before perihelion. The erratic behavior of the pre-perihelion jet sources as contrasted with the smoother variation from the rest of the surface after perihelion indicates there is a strong heterogeneity in the physical make-up of active areas on the nucleus.     

polarimetric and photometric observations of split comet C/2001 A2 (LINEAR)

We present the results of polarimetric and photometricobservations of split Comet C/2001 A2 (LINEAR), which wereobtained at the 70-cm telescope of the Astronomical Observatoryof Kharkiv National University between 30 June and 31 July 2001.The brightest fragment of the comet, nucleus B, was observed.Eight narrowband cometary filters in the continuum and in emissionbands and a wideband red filter have been used. The comet wasobserved through apertures of 88, 33, and 19 arcsec. Polarizationphase curves were obtained for the continuum and for the firsttime, for NH₂(0, 7, 0) emission. The degree of polarization ofthe light scattered by the dust decreases with the increase ofaperture size. An important temporal variation of the polarizationwith a rotation of the polarization plane was observed at twophase angles (26.5° and 36.2°). Molecular column densities and production rates of CN, C₂,C₃, and NH₂ species are calculated in the framework of theHaser model. A comparative analysis of the temporal variations ofthe visual magnitudes, gas and dust production rates, dust colorand polarization are presented.     

Pyroxenes microstructure in comet 81P/Wild 2 terminal Stardust particles

Abstract— We report the examination by transmission electron microscopy (TEM) of four Stardust terminal particles extracted from two neighboring tracks (32 an 69). The particles are made of well‐preserved crystalline grains dominated by low‐Ca pyroxene ranging from nearly pure enstatite to pigeonite. Some olivine grains are also found, in chemical equilibrium with the surrounding pyroxenes. Various microstructures are observed, as a function of the composition of the grains. They include (100)‐twinned pigeonite, clino/ortho domains in enstatite and exsolution in a Ca‐rich grain. The microstructures are mostly consistent with a formation by cooling from high‐temperature phases, which could be associated to igneous processes. Some dislocations in glide configuration are also present, probably attesting for small intensity shocks. Possible effects of the rapid heating/cooling stage and thermal shock associated to the collect are discussed. It appears that most of the microstructural features reported here are plausibly pristine.     

The dust coma of periodic comet Churyumov-Gerasimenko (1982 VIII)

The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ～2 × 10⁵ g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ～0.04 at 1.25 μm and ～0.05 at 2.2 μm.     

Evolution of C/2006 M4 (SWAN) comet tails

We studied variations in the structure of plasma and dust tails of the C/2006 M4 (SWAN) comet during a long observation period (September–December 2006). We found sizes of grains ejected by the comet from the synchronic-syndynamic analysis of comet images. We calculated solar wind speed for high heliographic latitudes from calculations of the aberration angle of the comet plasma tail. Rapid changes in the calculated values of the solar wind speed are caused by its variable transversal component.     

Polarimetric and photometric observations of comet C/1995 01 (hale-bopp)

Conclusions  From the results of our observations, we can say the following: the polarization decreased and the brightness increased during the observations (Fig. 1). There is no definite relationship between the polarization parameters (P, θ ) and wavelength λ (U, B, V, R). The authors wish to thank L. G. Akhverdian for providing the photograph in Fig. 2. Translated from Astrofizika, Vol. 41, No. 2, pp. 311–315, April-June, 1998.     

Minor elements in forsterites of Orgueil (C1), Alais (C1) and two interplanetary dust particles compared to C2-C3-UOC forsterites

Abstract— The rare Mg-rich silicate fraction of the C1 meteorites, Orgueil and Alais, is dominated by minute (< 30 μm) forsterite. Twenty three forsterite grains of these meteorites as well as large forsterites in two chondritic porous interplanetary dust particles (IDPs) are characterized by levels of MnO generally, but not always, higher than found in forsterites of C2, C3 and unequilibrated ordinary chondrites (UOC). Forsterite in Orgueil contains 900 to 6200 ppmw MnO while Alais forsterite has less than 2000 ppmw MnO suggesting that the forsterites in the two meteorites are chemically distinct. Alais forsterite shows lower Cr and Al relative to Orgueil forsterite. The C1 forsterites do not show Fe-poor (FeO < 0.3), refractory-rich (Al, Ca, Ti, V) compositions which are relatively common in the C2-C3-UOC meteorites suggesting that the most primitive forsterite compositions are not present in these C1 meteorites. While minor elements in forsterite can not distinguish unambiguously between C1 and C2-C3-UOC sources, the high Mn levels in some IDP forsterites are similar to some C1 forsterites suggesting a possible relation between the forsterites of these two extraterrestrial samples.     

Gas and dust release from comet West (1976VI) nuclear fragments

Emission fluxes of CN, G₂ and C₃ carbon-bearing molecular species observed in the spectra of the nuclear fragment A and D of comet West (1976VI) are analysed in the framework of Haser's two-component model with radial outflow symmetry. Gas production rates have been derived and their ratios obtained. We find these vary as Q r ⁿ (where 1.0r2.6 is the heliocentric distance in AU) with photometric parametern = -4.11 (CN), -2.68 (C₂), -1.89 (C₃) andQ _x /Q _y r ⁿ withn = 2.22 (C₃/CN), 1.42 (C₂/CN), -0.79 (C₂/C₃). The gas-to-dust ratio, dust production rates in arbitrary units, total number of dust particles in the field of view and an effective radius R_eff 2.0 km for the principal nuclear fragmentA is also estimated.     

Comet Sugano-Saigusa-Fujikawa (1983V)--a small, puzzling comet

Spectroscopic and infrared observations of Comet Sugano-Saigusa-Fujikawa (1983V) were obtained during its close approach to the Earth on 11-14 June 1983. The [O I] production rates of 1.8 +/- 0.9 x 10(26) atoms/s observed on 12.3 June and 7 +/- 3.5 x 10(26) atoms/s on 13.4 June lead to derived water-production rates of 3 x 10(27) mol/s on 12 June and 1.1 x 10(28) mol/s on 13 June. The abundances of the minor species NH2, CN, C2, and C3 are unusually low relative to [O I]. The upper limit to the average nuclear radius from our infrared and visual photometry on 12-13 June (assuming that the entire signal came from the nucleus) is approximately 370 m. The dust/gas mass ratio was <0.01 on June 12 and <0.005 on June 13.     

Spectrophotometric study of comet Austin (1989 C1)

Spectrophotometric observations of the head of comet Austin (1989 C1) during five nights in May 1990 are presented. Emission bands due to CN, C₂ and C₃ molecules have been identified. An estimate of their column densities and production rates have been made.     

DE-like event in the plasma tail of comet C/2006 M4 (SWAN)

We investigate a DE-like event of October 27, 2006, in the plasma tail of comet C/2006 M4 (SWAN). A set of phenomena in the comet??s tail after the brightness outburst on October 24.04, 2006, is described. The typical dimensions of the tail structure details that developed as a result of plasma instabilities are found. The velocity and acceleration of the disconnected tail fragment and the beginning time of the event are determined. The likely cause of the DE-like event is the comet??s encounter with a high-speed stream of solar wind.     

Photometric studies of comet C/2009 P1 (Garradd) before the perihelion

The results of the photometric observations of comet C/2009 P1 (Garradd) performed at the 60-cm Zeiss-600 telescope of the Terskol observatory have been analyzed. During the observations, the comet was at the heliocentric and geocentric distances of 1.7 and 2.0 AU, respectively. The CCD images of the comet were obtained in the standard narrowband interference filters suggested by the International research program for comet Hale-Bopp and correspondingly designated the “Hale-Bopp (HB) set.” These filters were designed to isolate the BC (λ4450/67 Å), GC (λ5260/56 Å) and RC (λ7128/58 Å) continua and the emission bands of C₂ (λ5141/118 Å), CN (λ3870/62 Å), and C₃ (λ4062/62 Å). From the photometric data, the dust production rate of the comet and its color index and color excess were determined. The concentration of C₂, CN, and C₃ molecules and their production rates along the line of sight were estimated. The obtained results show that the physical parameters of the comet are close to the mean characteristics typical of the dynamically new comets.