This study investigates the extinction properties, dust distribution, and magnetic field characteristics of the CB26 cloud. Extinction mapping, derived from near-infrared photometry, reveals a good correlation with the dust distribution, as traced by HerschelSPIRE 500 mu m data, indicating a close link between dust and extinction. The derived column density estimates align with previous Herschel studies. Our optical polarization observations of CB26 reveal a well-aligned magnetic field in the cloud's low-density envelope, closely following the Galactic plane. In contrast, our reanalysis of archival submillimetre polarization data of CB26 suggests a distinct magnetic field orientation within the cloud core. The offset angle between the core and Galactic magnetic fields is approximately 90(omicron) suggesting a decoupling of the core's magnetic field from the large-scale Galactic field. A relationship is found between polarization rate and distance for 24 field stars in CB26, suggesting that most of the polarization is contributed by dust within 600 pc along the line of sight.

The concept of Fermi–Dirac statistics has been applied to correlate between the electronic entropy and spatial confinement of liquid crystal-perovskite nanohybrids as model condensed matter systems.

This study investigates the influence of porosity on the Umov effect, a phenomenon observed in the scattering of light from celestial objects. The Umov effect describes an inverse relationship between the degree of linear polarization and the object’s reflectance (geometric albedo). To study the dependence of porosity on the Umov effect, a wide range of porosity (i.e., from 0.64 to 0.99) is considered. Four types of aggregates, ballistic cluster-cluster aggregate (BCCA), ballistic particle cluster aggregate (BPCA) or ballistic agglomeration (BA), ballistic agglomeration with one migration (BAM1), and ballistic agglomeration with two migrations (BAM2) each having porosity 0.99, 0.87, 0.74, and 0.64 are considered in this study. The multi-sphere T-matrix code is utilized to calculate the linear polarization and geometric albedo (A) considering silicate and organic refractory compositions for monodisperse aggregates. The results are reported for six different wavelengths, ranging from near-ultraviolet to the visible spectrum. When the polarization maximum (Pmax) is plotted against the geometric albedo (A) on a logarithmic scale, an inverse relation is observed. This relation exhibits non-linear changes, fitted by a second-degree polynomial equation, as the porosity changes from 0.64 to 0.99. This finding constitutes one of the interesting results of our study. In addition, the study explores the effect of porosity (P) on the ratio between log(Pmax) and log(A), showing a non-linear relationship. A comparison is drawn between the results obtained from organic refractory compositions and amorphous silicate compositions, emphasizing the importance of porosity and wavelength in regulating the Umov effect. In addition, the research investigates how mixing affects the results at different wavelengths, assuming the aggregates are blends of organic refractory and amorphous silicate compositions. The computations have also been performed for polydisperse aggregates (considering BCCA, BA, BAM1, and BAM2 structures) at a wavelength of 0.45 μm for silicate compositions, which also showed a non-linear dependence as observed in the case of monodisperse aggregates.

The cosmic dust particles found in space are mainly porous aggregates of smaller grains. Theoretically, these aggregates are replicated using fractal geometry, assuming a cluster of spheres. Although the light scattering response of cosmic dust aggregates has been thoroughly studied using clusters of spherical grains in the past few decades, the effect of irregularities on the surface of each grain in an entire aggregate has mostly been neglected. We introduce, for the first time, a visually realistic cosmic dust model that incorporates a mixture of rough fractal aggregates (RFA) and agglomerated debris (Solids) to replicate the unusual polarization–phase curve observed in the case of the interstellar comet 2I/Borisov at multiple wavelengths. The authenticity of the RFA structures has been verified by replicating light scattering results of circumstellar dust analogs from the Granada Amsterdam Light Scattering Database. We demonstrate that the light scattering response from the RFA structures has a very close resemblance to the experimental values. Finally, we model the observed polarization–phase curve of the interstellar comet 2I/Borisov using a mixture of RFA and solid particles. The best-fit data indicate the presence of a higher percentage of porous RFA structures (80%) owing to the fact that the comet carries a higher percentage of small and highly porous pristine cosmic dust particles. Further, the model indicates that the unusually steep polarimetric slope and the high dust-to-gas ratio in newer comets are mainly due to a higher porous-to-compact ratio.

We present the results obtained from photometric and polarimetric observation of a Jupiter family comet 32P/Comas Sola, and a Oort cloud comet C/2015 V2 (Johnson), observed on February 20, 2015 (post-perihelion) and December 30, 2016 (pre-perihelion), at phase angles 9.8∘ and 21.6∘. Both the comets show a diffuse coma in the intensity map which extends towards the tailward direction. To study the morphological structures of both the comets, intensity images are treated with digital filters. A V-shaped structure is noticed in the antisolar direction of comet 32P/Comas Sola which appears due to radial outflow of dust from the nucleus. The comet C/2015 V2 (Johnson) shows some structures with fan-shaped fine jets in the antisolar direction. It is also noticed that intensity is found to be higher in the tailward direction as compared to sunward direction in both comets. The average polarization value is estimated to be ( $-1.0\pm 0.7$ )% at aperture radius ∼ 13,500 km for comet 32P/Comas Sola and ( $-0.4 \pm 0.7$ )% at aperture radius ∼ 12,600 km for comet C/2015 V2 (Johnson). The observed polarization values obtained from this work are compared with other comets at almost similar phase angles which showed a satisfactory agreement within the framework of the estimated errors in polarization.

Comet 156P/Russell-LINEAR is a short period Jupiter family comet with an orbital period of 6.44 years. The results from spectroscopic, photometric, polarimetric observations and dust modelling studies are presented here. From the spectroscopic study, strong emissions from CN(Δν=0), C3 (λ4050 Å), C2(Δν=+1) and C2(Δν=0) can be observed during both the epochs of our observations. The Q(C2)/Q(CN) ratio classifies the comet as a typical comet. The imaging data reveals the presence of jets. The dust emission from the comet is observed to have a non-steady state outflow due to the presence of these strong jets which subside in later epochs, resulting in a steady state outflow. Polarimetric study at two different phase angles reveals the degree of polarization to be comparable to Jupiter family comets at similar phase angles. Localized variations in polarization values are observed in the coma. The dust modelling studies suggest the presence of high amount of silicate/low absorbing material and indicate the coma to be dominated by higher amount of large size grains with low porosity having power law size distribution index = 2.4. The observed activity and dust properties points to a similarity to another Jupiter family comet, 67P/Churyumov–Gerasimenko.

The overall understanding of cosmic dust particles is mainly inferred from the different Earth-based measurements of interplanetary dust particles and space missions such as Giotto, Stardust, and Rosetta. The results from these measurements indicate the presence of a wide variety of morphologically significant dust particles. To interpret the light-scattering and thermal emission observations arising due to dust in different regions of space, it is necessary to generate computer-modeled realistic dust structures of various shapes, sizes, porosity, bulk density, aspect ratio, and material inhomogeneity. The present work introduces a Java package called Rough Ellipsoid Structure Tool (REST), which is a collection of multiple algorithms, that aims to craft realistic rough-surface cosmic dust particles from spheres, superellipsoids, and fractal aggregates depending on the measured bulk density and porosity. Initially, spheres having N ( d ) dipoles or lattice points are crafted by selecting random material and space seed cells to generate a strongly damaged structure, rough surface, and poked structure. Similarly, REST generates rough-surface superellipsoids and poked structure superellipsoids from initial superellipsoid structures. REST also generates rough fractal aggregates, which are fractal aggregates having rough-surface irregular grains. REST has been applied to create agglomerated debris, agglomerated debris superellipsoids, and mixed-morphology particles. Finally, the light-scattering properties of the respective applied structures are studied to ensure their applicability. REST is a flexible structure tool that shall be useful for generating various types of dust structures that can be applied to studying the physical properties of dust in different regions of space.

This article announces the development of the third version of the Java Superposition T-matrix App (JaSTA-3), to study the light scattering properties of heterogeneous aggregate particles. It has been developed using Netbeans 7.1.2, which is a Java integrated development environment (IDE). The JaSTA uses double precision superposition codes for multi-sphere clusters in random orientation, developed by Mackowski and Mischenko (1996). The new version consists of three options as part of the input parameters: (i) single wavelength, (ii) multiple wavelengths and (iii) Heterogeneous geometry. The first and second options (which retain the applicability of older versions of JaSTA) calculate the light scattering properties of aggregates of spheres for single and multiple wavelengths for randomly oriented particles, whereas the third option can execute light scattering simulations for heterogeneous aggregates (polydisperse and inhomogeneous) for multiple number of wavelengths in a single run over both random orientation and fixed orientation. JaSTA-3 is a major update of the application that aims to provide light scattering feed for more complex aggregates that can be used in diverse fields like Astrophysics, Planetary Science, Atmospheric Science, Nanoscience, etc. This version of the software is developed for Linux platform only, and it can take advantage of all the cores of a processor using the multi-threading option.

ABSTRACT In this work, we introduce a comet dust model that incorporates multiple dust morphologies along with inhomogeneous mixture of silicate minerals and carbonaceous materials under power-law size distribution, to replicate the standard polarization-phase curve observed in several comets in the narrow-band continuum. Following the results from Rosetta/midas and COSIMA, we create high porosity hierarchical aggregates (HA) and low porosity (<10 per cent) Solids in the form of agglomerated debris. We also introduce a moderate porosity structure with solids in the core, surrounded by fluffy aggregates called fluffy solids (FS). We study the mixing combinations, (HA and Solids), (HA and FS), and (HA, FS, and Solids) for a range of power-law index n= 2.0 to 3.0 for different sets of mixing percentage of silicate minerals and carbonaceous materials. Polarimetry of the short period comets 1P/Halley and 67P/Churyumov-Gerasimenko match best with the polarization resulting from the combination of HA and Solids while the combinations (HA and FS) and (HA, FS, and Solids) provide the best-fitting results for the long period comets C/1995 O1 (Hale-Bopp) and C/1996 B2 (Hyakutake). The best-fitting model results also recreate the observed wavelength dependence of polarization. Our dust model agree with the idea that the long period comets may have high percentage of loose particles (HA and FS) compared to those in the case of short period comets as the short period comets experience more frequent and/or higher magnitude of weathering.

We investigate the effect of porosity in the Umov effect for the first time using the aggregate dust model. The Umov effect is an inverse correlation between the reflectivity (or geometric albedo) of an object and the degree of linear polarization of light scattered by it. Three different types of fractal aggregates: ballistic agglomeration (BA), ballistic agglomeration with one migration (BAM1), and ballistic agglomeration with two migrations (BAM2) having porosities 0.87, 0.74, and 0.64, respectively (which have the same characteristic radius similar to 1 mu m), are considered in our simulations. Using the multisphere T-matrix (mstm) code, maximum positive polarization (P-max) and geometric albedo (A) are calculated for three different fractal aggregated structures considering amorphous silicate composition. Then P-max and A are plotted against each other in logarithmic scale that shows a linear inverse correlation and a strong porosity dependence. This study shows that the porosity of the aggregates plays a crucial role in the Umov-law diagram. Further, we explore the effect of aggregate size parameter and the effect of composition in the Umov diagram for particles larger than the wavelength of incident radiation. A systematic study is presented in this paper.

In this work, we study the light scattering properties of dust aggregates (0.7 mu m less than or similar to R-c less than or similar to 2.0 mu m) with a wide range of porosity (P = 0.59 to 0.98). The simulations are executed using the Superposition T-matrix code with BCCA, BA, BAM1 and BAM2 clusters of varying porosity. We investigate the nature and dependencies of the different scattering parameters on porosity, size and composition of the aggregated particles for wavelengths 0.45 mu m and 0.65 mu m. We find that the scattering parameters are strongly correlated with the porosity of the aggregated structures. Our results indicate that, when the porosity of the aggregates decreases, keeping characteristic radius of the aggregates (R-c) same for all structures, there is an enhancement in the negative polarization branch (NPB) which is accompanied by a substantial increase in the anisotropies present in the material. Also at the exact backscattering region, the anisotropies are found to be linearly correlated with the porosity of the aggregated structure. The computational study reveals that, for low absorbing materials (k <= 0.1), the negative polarization minimum (P-min) is strongly correlated with the associated anisotropies. Finally, we put forward a qualitative comparison between our computationally obtained results and some selected data from the Amsterdam Light Scattering Database for both low and high absorbing materials. The experimental results also suggest that an increase in the NPB is always accompanied by an enhancement in the anisotropy at the backscattering region. (C) 2018 Elsevier Inc. All rights reserved.

In this article, we announce the development of a new version of the Java Superposition T-matrix App (JaSTA-2), to study the light scattering properties of porous aggregate particles. It has been developed using Netbeans 7.1.2, which is a java integrated development environment (IDE). The JaSTA uses double precision superposition T-matrix codes for multi-sphere clusters in random orientation, developed by Mackowski and Mischenko (1996). The new version consists of two options as part of the input parameters: (i) single wavelength and (ii) multiple wavelengths. The first option (which retains the applicability of older version of JaSTA) calculates the light scattering properties of aggregates of spheres for a single wavelength at a given instant of time whereas the second option can execute the code for a multiple numbers of wavelengths in a single run. JaSTA-2 provides convenient and quicker data analysis which can be used in diverse fields like Planetary Science, Atmospheric Physics, Nanoscience, etc. This version of the software is developed for Linux platform only, and it can be operated over all the cores of a processor using the multi-threading option.

We study the light scattering properties of moderately large dust aggregates (\(0.8~\upmu \mbox{m} \lesssim R \lesssim 2.0~\upmu \mbox{m}\)) with a wide variation of porosity (\(\mathcal{P}\)) from 0.57 to 0.98. The computations are performed using the Superposition T-matrix code with BAM2 cluster (\(\mathcal{P} \sim 0.57\mbox{--}0.64\)), BAM1 cluster (\(\mathcal{P} \sim 0.74\)), BA or BPCA cluster (\(\mathcal{P} \sim 0.85\mbox{--}0.87\)) and BCCA cluster (\(\mathcal{P} \sim 0.98\)). The simulations are executed at two wavelengths \(0.45~\upmu \mbox{m}\) and \(0.65~\upmu \mbox{m}\) with highly absorbing particles (organic refractory) as well as with low absorbing particles (amorphous silicates) to understand the photopolarimetric behavior (phase function, polarization, and color) of dust aggregates. The effect of aggregate size parameter (\(X\)) on the light scattering properties of aggregates (BA and BAM2) having different porosities is explored in this study. We find that the positive polarization maximum (\(P_{\max}\)), the amplitude of the negative polarization (\(P_{\min}\)) and phase function at the exact backscattering direction (\(S_{11}(180^{\circ })\)) are correlated with the porosity of aggregates. Compact aggregates show deeper negative polarization as compared to porous aggregates when the characteristic radius (\(R\)) of the aggregates are considered to be the same. Further lower porosity aggregates show higher \(S_{11}(180^{\circ })\) and vice versa. When \(\mathcal{P}\) is increased in a range from 0.64 to 0.98, both \({S}_{11}(180^{\circ })\) and \(P_{\min}\) decrease linearly, whereas \(P_{\max}\) increases linearly. We also find that the porosity of the aggregates plays a crucial role in determining the polarimetric color for high absorbing organic refractories. The compact clusters (BAM1 and BAM2) show the negative polarimetric color whereas BA clusters show almost positive polarimetric color at all values of scattering angle. We have also made some comparisons of our simulated results with PROGRA2 experimental results.

We report the results obtained from the optical polarimetric study of the light scattered by comets C/2013 V1 (Boattini) and 290P/Jager at lower phase angles. The polarimetric observations of two comets have been performed with the 1.04-m Sampurnanand telescope of Aryabhatta Research Institute of observational sciencES near Nainital in India on 2013 December 4 and 5 and on 2014 April 24 using R photometric band ($\lambda$ = 630 nm, $\Delta$$\lambda$ =120nm). We covered observations in both the pre and post perihelion passage of comets C/2013 V1 (Boattini) and 290P/Jager at two phase angles $\sim$ 13$^\circ$ and 27$^\circ$. The degree of polarization changes from ($-1.4$$\pm 0.3$)per cent to (+2.8$\pm 0.5$)per cent for comet C/2013 V1 (Boattini) and ($-1.6$$\pm 0.5$)per cent to (+2.5$\pm 0.5$)per cent for comet 290P/Jager at phase angles $\sim$ 13$^\circ$ and 27$^\circ$ respectively. The change in the physical properties of cometary dust is being well studied from the polarization maps obtained for both the period of observations. It is found that the aperture polarization values are comparable to those of other comets. The variation in the brightness profile of both the comets from the standard canonical nature is also being observed in both the solar and anti-solar direction during this phase which suggests the various physical evolution influencing the cometary comae.

In this paper, we report the development of a java application for the Superposition T-matrix code, JaSTA (Java Superposition T-matrix App), to study the light scattering properties of aggregate structures. It has been developed using Netbeans 7.1.2, which is a Java integrated development environment (IDE). The JaSTA uses double precession superposition codes for multi-sphere clusters in random orientation developed by Mackowski and Mischenko (1996). It consists of a graphical user interface (GUI) in the front hand and a database of related data in the back hand. Both the interactive GUI and database package directly enable a user to model by self-monitoring respective input parameters (namely, wavelength, complex refractive indices, grain size, etc.) to study the related optical properties of cosmic dust (namely, extinction, polarization, etc.) instantly, i.e., with zero computational time. This increases the efficiency of the user. The database of JaSTA is now created for a few sets of input parameters with a plan to create a large database in future. This application also has an option where users can compile and run the scattering code directly for aggregates in GUI environment. The JaSTA aims to provide convenient and quicker data analysis of the optical properties which can be used in different fields like planetary science, atmospheric science, nano science, etc. The current version of this software is developed for the Linux and Windows platform to study the light scattering properties of small aggregates which will be extended for larger aggregates using parallel codes in future.Program SummaryProgram title: JaSTA: Java Superposition T-matrix App.Catalogue identifier: AETB_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AETB_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 571570No. of bytes in distributed program, including test data, etc.: 120226886Distribution format: tar.gzProgramming language: Java, Fortran95.Computer: Any Windows or Linux systems capable of hosting a java runtime environment, java3D and fortran95 compiler; Developed on 2.40 GHz Intel Core i3.Operating system: Any Windows or Linux systems capable of hosting a java runtime environment, java3D and fortran95 compiler.RAM: Ranging from a few Mbytes to several Gbytes, depending on the input parameters.Classification: 1.3.External routines: jfreechart-1.0.14 [1] (free plotting library for Java), j3d-jre-1.5.2 [2] (3D visualization).Nature of problem: Optical properties of cosmic dust aggregates.Solution method: Java application based on Mackowsld and Mischenko's Superposition T-Matrix code.Restrictions: The program is designed for single processor systems.Additional comments: The distribution file for this program is over 120 Mbytes and therefore is not delivered directly when Download or Email is requested. Instead a html file giving details of how the program can be obtained is sent.Running time: Ranging from few minutes to several hours, depending on the input parameters.References:[1] http://www.jfree.org/index.html[2] https://java3d.java.net/ (C) 2014 Elsevier B.V. All rights reserved.