Interplay of dust alignment, grain growth, and magnetic fields in polarization: lessons from the emission-to-extinction ratio

Context. Current dust models are challenged by the dust properties inferred from the analysis of Planck observations in total and polarized emission. Aims. We propose new dust models compatible with polarized and unpolarized data in extinction and emission for translucent lines of sight (0.5 < AV < 2.5). Methods. We amended the DustEM tool to model polarized extinction and emission. We fit the spectral dependence of the mean extinction, polarized extinction, total and polarized spectral energy distributions (SEDs) with polycyclic aromatic hydrocarbons, astrosilicate and amorphous carbon (a-C) grains. The astrosilicate population is aligned along the magnetic field lines, while the a-C population may be aligned or not. Results. With their current optical properties, oblate astrosilicate grains are not emissive enough to reproduce the emission to extinction polarization ratio P353∕pV derived with Planck data. Successful models are those using prolate astrosilicate grains with an elongation a∕b = 3 and an inclusion of 20% porosity. The spectral dependence of the polarized SED is steeper in our models than in the data. Models perform slightly better when a-C grains are aligned. A small (6%) volume inclusion of a-C in the astrosilicate matrix removes the need for porosity and perfect grain alignment, and improves the fit to the polarized SED. Conclusions. Dust models based on astrosilicates can be reconciled with Planck data by adapting the shape of grains and adding inclusions of porosity or a-C in the astrosilicate matrix.

This study examines the relationship between the magnetic field orientation of a molecular cloud and its outflow axis, using data from 22 molecular clouds. We find that the position angles of the outflow axis ($\theta _{\text{out}}$) and the cloud-scale magnetic field in the core, measured in the submillimetre region ($\theta _B^{\text{sub}}$), are correlated to each other irrespective of the alignment or misalignment between the two axes. However, it is important to note that these observed position angles are projections on to the plane of the sky. To assess the statistical significance of our findings, we conduct a statistical test to account for the projection effect and find minimal impact. Moreover, we identify a possible role of the Galactic magnetic field orientation ($\theta _{\text{GP}}$) in determining the outflow direction by assessing the offset ($\theta _{\text{off}} = \theta _B - \theta _{\text{GP}}$) in both the core and envelope regions. Furthermore, we explore the influence of parameters such as magnetic field strength (B), the position angle of the minor axis of the cloud cores ($\theta _{\text{min}}$), the inclination angle of the outflow ($i_{\text{out}}$), and other factors on the alignment between the outflow and cloud-scale magnetic field axes ($|\theta _{\text{OB}}| = |\theta _{\text{out}} - \theta _B^{\text{sub}}|$). Our analysis suggests that the orientation of the outflow axis is determined by the combined influence of the magnetic field orientation, the minor axis, the inclination angle of the outflow, and the associated magnetic field strength.

We present 450 {\\mu}m polarimetric observations of the M17 molecular cloud\nobtained with the SHARP polarimeter at the Caltech Submillimeter Observatory.\nAcross the observed region, the magnetic field orientation is consistent with\nprevious submillimeter and far-infrared polarization measurements. Our\nobservations are centered on a region of the molecular cloud that has been\ncompressed by stellar winds from a cluster of OB stars. We have compared these\nnew data with previous 350 {\\mu}m polarimetry and find an anti-correlation\nbetween the 450 to 350 {\\mu}m polarization magnitude ratio and the ratio of 21\ncm to 450 {\\mu}m intensity. The polarization ratio is lower near the east end\nof the studied region where the cloud is exposed to stellar winds and\nradiation. At the west end of the region, the polarization ratio is higher. We\ninterpret the varying polarization spectrum as evidence supporting the\nradiative alignment torque (RAT) model for grain alignment, implying higher\nalignment efficiency in the region that is exposed to a higher anisotropic\nradiation field.\n

Systematic variations with wavelength in the position angle of interstellar linear polarization of starlight may be indicative of multiple cloud structure along the line of sight. We use polarimetric observations of two stars (HD 29647 and HD 283809) in the general direction of TMC-1 in the Taurus dark cloud to investigate grain properties and cloud structure in this region. We show the data to be consistent with a simple two-component model in which general interstellar polarization in the Taurus cloud is produced by a widely distributed cloud component with relatively uniform magnetic field orientation; light from stars close to TMC-1 suffers additional polarization arising in one (or more) subcloud(s) with larger average grain size and magnetic field directions different from the general trend. Toward HD 29647 in particular, we show that the unusually low degree of visual polarization relative to extinction is due to depolarization associated with the presence of distinct cloud components in the line of sight with markedly different magnetic field orientations. Stokes parameter calculations allow us to separate the polarization characteristics of the individual components. Results are fitted with the Serkowski empirical formula to determine the degree and wavelength of maximum polarization. Whereas λmax values in the widely distributed material are similar to the average (0.55 μm) for the diffuse interstellar medium, the subcloud in the line of sight to HD 283809, the most heavily reddened star in our study, has λmax ≈ 0.73 μm, indicating the presence of grains ~30% larger than this average. Our model also predicts detectable levels of circular polarization toward both HD 29647 and HD 283809.

Observational results of interstellar and intergalactic magnetic fields are reviewed, including the fields in supernova remnants and loops, interstellar filaments and clouds, Hii regions and bubbles, the Milky Way and nearby galaxies, galaxy clusters, and the cosmic web. A variety of approaches are used to investigate these fields. The orientations of magnetic fields in interstellar filaments and molecular clouds are traced by polarized thermal dust emission and starlight polarization. The field strengths and directions along the line of sight in dense clouds and cores are measured by Zeeman splitting of emission or absorption lines. The large-scale magnetic fields in the Milky Way have been best probed by Faraday rotation measures of a large number of pulsars and extragalactic radio sources. The coherent Galactic magnetic fields are found to follow the spiral arms and have their direction reversals in arms and interarm regions in the disk. The azimuthal fields in the halo reverse their directions below and above the Galactic plane. The orientations of organized magnetic fields in nearby galaxies have been observed through polarized synchrotron emission. Magnetic fields in the intracluster medium have been indicated by diffuse radio halos, polarized radio relics, and Faraday rotations of embedded radio galaxies and background sources. Sparse evidence for very weak magnetic fields in the cosmic web is the detection of the faint radio bridge between the Coma cluster and A1367. Future observations should aim at the 3D tomography of the large-scale coherent magnetic fields in our Galaxy and nearby galaxies, a better description of intracluster field properties, and firm detections of intergalactic magnetic fields in the cosmic web.

Enhancement of thermal conductivity and kinematic viscosity in magnetically controllable maghemite (γ-Fe2O3) nanofluids

Measurement of the plastic scintillator response in the magnetic field

Magnetic fields, while ubiquitous in many astrophysical environments, are challenging to measure observationally. Based on the properties of anisotropy of eddies in magnetized turbulence, the Velocity Gradient Technique is a method synergistic to dust polarimetry that is capable of tracing plane-of-the-sky magnetic field, measuring the magnetization of interstellar media and estimating the fraction of gravitational collapsing gas in molecular clouds using spectral line observations. In this paper, we apply this technique to five low-mass star-forming molecular clouds in the Gould Belt and compare the results to the magnetic-field orientation obtained from polarized dust emission. We find the estimates of magnetic field orientations and magnetization for both methods are statistically similar. We estimate the fraction of collapsing gas in the selected clouds. By means of the Velocity Gradient Technique, we also present the plane-of-the-sky magnetic field orientation and magnetization of the Smith cloud, for which dust polarimetry data are unavailable.

We investigate the effects of magnetic and crystalline anisotropies on the\ntopological superconducting state of planar Josephson junctions (JJs). In\njunctions where only Rashba spin-orbit coupling (SOC) is present, the\ntopological phase diagram is insensitive to the supercurrent direction, but\nexhibits a strong dependence on the magnetic field orientation. However, when\nboth Rashba and Dresselhaus SOCs coexist, the topological phase diagram\nstrongly depends on both the magnetic field and junction crystallographic\norientations. We examine the impact of the magnetic and crystalline anisotropy\non the current-phase relation (CPR), energy spectrum, and topological gap of\nphase-biased JJs, where the junction is connected in a loop and the\nsuperconducting phase difference is fixed by a loop-threading magnetic flux.\nThe anisotropic CPR can be used to extract the ground-sate phase (i.e. the\nsuperconducting phase difference that minimizes the system free energy)\nbehavior in phase-unbiased JJs with no magnetic flux. Under appropriate\nconditions, phase-unbiased JJs can self-tune into or out of the topological\nsuperconducting state by rotating the in-plane magnetic field. The magnetic\nfield orientations at which topological transitions occur strongly depend on\nboth the junction crystallographic orientation and the relative strength\nbetween Rashba and Dresselhaus SOCs. We find that for an optimal practical\napplication, in which the junction exhibits topological superconductivity with\na sizable topological gap, a careful balancing of the magnetic field direction,\nthe junction crystallographic orientation, and the relative strengths of the\nRashba and Dresselhaus SOCs is required. We discuss the considerations that\nmust be undertaken to achieve this balancing for various junction types and\nparameters.\n

Israeli agriculture has experienced rapid structural changes in recent decades, including the massive exit of farmers, a resulting increase in average farm size, a higher farm specialization and a higher reliance on non-farm income sources. The higher farm heterogeneity makes it necessary to examine changes in the entire farm size distribution rather than the common practice of analyzing changes in the average farm size alone. This article proposes a nonparametric analysis in which the change in the distribution of farm sizes between two periods is decomposed into several components, and the contributions of subgroups of farms to this change are analyzed. Using data on Israeli family farms, we analyze the changes in the farm size distribution in two separate time periods that are characterized by very different economic environments, focusing on the different contributions of full-time farms and part-time farms to the overall distributional changes. We found that between 1971 and 1981, a period characterized by stability and prosperity, the farm size distribution has shifted to the right with relatively minor changes in higher moments of the distribution. On the other hand, between 1981 and 1995, a largely unfavorable period to Israeli farmers, the change in the distribution was much more complex. While the overall change in the size distribution of farms was smaller in magnitude than in the earlier period, higher moments of the distribution were not less important than the increase in the mean and led to higher dispersion of farm sizes. Between 1971 and 1981, the contributions of full- and part-time farms to the change in the size distribution were quite similar. Between 1981 and 1995, however, full-time farms contributed mostly to the growth in the average farm size, while the average farm size among part-time farms actually decreased, and their contribution to the higher dispersion of farm sizes was quantitatively larger. This highlights the need to analyze the changes in the entire farm size distribution rather than focusing on the mean alone, and to allow for differences between types of farms.

We have performed multiband photopolarimetry toward stars behind the molecular cloud L1457 (MBM 12). This cloud is the nearest known molecular cloud (65 pc) and is thought to be contained within the local "hot bubble." The polarization shows a regular structure, indicating that the cloud is threaded by an ordered magnetic field. The wavelength dependence of the polarization seems to indicate that the grains in L1457 have higher indices of refraction than normal for interstellar clouds. However, the wavelength of maximum polarization indicates that their size distribution is close to normal.

IntroductionIn recent years, the discovery of more exoplanetary systems and interstellar objects has highlighted the growing synergy between exoplanetary science and planetary science. While exoplanetary science offers statistical insights into planetary architectures and formation scenarios, planetary science provides detailed physical models essential for the characterization of exoplanets [1]. Planet formation, whether in our Solar System or around other stars, is strongly influenced by the initial conditions of protoplanetary disks (PPDs)—including masses, sizes, surface densities, and temperature profiles [10]. In addition to that, the subsequent evolution of these PPDs is governed by processes such as radial drift, vertical mixing, and, in particular, grain growth [2].One of the major challenges in planet formation is understanding how dust grains grow into millimeter- to centimeter-sized particles. Such large grains—found in comets—serve as local analogs to the solids observed in disks around young stars [3] and provide a unique opportunity to investigate early grain growth processes. However, studies of these particles, which also constitute the bulk of the total coma mass [4], remain largely unexplored. Large particles also contribute to the grain size distribution, which plays a critical role in estimating the total dust mass in PPDs. Accurate dust mass estimates are essential to evaluate the potential to form planetesimals, rocky planets, and giant planet cores [5]. However, the current dust mass estimates are highly uncertain and insufficient to explain the observed high incidence of massive exoplanets [6,7].These challenges—uncertainties in PPD dust masses and limited characterization of large particles—can be addressed through multi-frequency analysis of dust in both protoplanetary disks and comets. Although numerous studies have individually investigated dust properties in each of these environments, comparative analyses integrating exoplanetary and planetary science remain understudied. Such interdisciplinary comparisons of dust properties have the potential to significantly improve our understanding of the processes governing the evolution of planetary systems.Observations and MethodsAs part of the ODISEA project (Ophiuchus DIsk Survey Employing ALMA) [8], we combined the archival ALMA observations across Band 3 (100 GHz), Band 4 (140 GHz), Band 6 (230 GHz), Band 7 (350 GHz), and Band 8 (410 GHz). This multi-frequency approach allows us to constrain dust temperatures, surface densities, and grain size distributions as a function of radius [9]. This is in contrast to the single-frequency approach, which requires assuming a single temperature and optically thin emission. Our method is based on the radiative transfer equation under the plane-parallel slab approximation, which is given by:Iν = Bν (Td) [1 - exp (-τ0 (ν/ν0) β)]where Bν(Td) is the Planck function, Td is the dust temperature, τ0 is the optical depth of dust at frequency ν0, and β is the dust opacity spectral index. This framework, therefore, enables more robust dust mass estimates by integrating over the surface density profile.To extend this analysis to the solar system context, we apply a similar multi-frequency approach to study the dust properties in comets. Using a similar set of ALMA bands, we target the distribution of dust and the presence of large grains in the comae of the exceptionally bright Oort Cloud comets, C/2023 A3 and C/2017 K2. These long-period comets are among the least thermally processed bodies in the Solar System and are also known to be dust-rich, making them one of the best-preserved reservoirs of primitive material from the solar nebula. Our observations aim to constrain the dust mass-loss rate and model the spectral energy distribution (SED) to derive the grain size distribution and dust structure. Additionally, we obtained mid-infrared observations of comet A3 with VLT’s VISIR instrument to investigate the long-standing contradiction of detecting crystalline silicates, formed at high temperatures, in comets that originated in cold environments.I will present the analysis of dust continuum from both A3 and K2 based on our ALMA observations, alongside key results of their composition from mid-infrared spectral fitting using dust models. In parallel, I will present the statistical results on dust surface density, maximum grain size, and dust temperature profiles in PPDs, emphasizing the comparison between dust masses derived from single- versus multi-frequency analyses. This represents the first comprehensive multi-frequency study of a large sample of 44 Class I and Class II disks, corresponding to the early stages of PPD evolution, within a single molecular cloud. Finally, I will discuss how integrating findings from both cometary and disk environments through consistent multi-frequency analysis helps bridge a critical knowledge gap in our understanding of grain growth, the role of large particles, and the evolution of dust properties across different stages of planetary system formation.

We present a novel statistical analysis aimed at deriving the intrinsic shapes and magnetic field orientations of molecular clouds using dust emission and polarization observations by the Hertz polarimeter. Our observables are the aspect ratio of the projected plane-of-the-sky cloud image, and the angle between the mean direction of the plane-of-the-sky component of the magnetic field and the short axis of the cloud image. To overcome projection effects due to the unknown orientation of the line-of-sight, we combine observations from 24 clouds, assuming that line-of-sight orientations are random and all are equally probable. Through a weighted least-squares analysis, we find that the best-fit intrinsic cloud shape describing our sample is an oblate disk with only small degrees of triaxiality. The best-fit intrinsic magnetic field orientation is close to the direction of the shortest cloud axis, with small (~24 deg) deviations toward the long/middle cloud axes. However, due to the small number of observed clouds, the power of our analysis to reject alternative configurations is limited.

Molecular clouds are sites of star formation. Magnetic fields are believed to play an important role in their dynamics and shaping morphology. We aim to study any possible correlation that might exist between the magnetic fields orientation inside the clouds and the magnetic fields at envelope scales and their connection with respect to the observed morphology of the selected clouds. We examine the magnetic field orientation towards the clouds L1512, L1523, L1333, L1521E, L1544, L1517, L1780, and L183, using optical and Planck polarization observations. We also found the correlation between the ambient magnetic field and core orientations derived using Astrodendrogram on the Herschel 250 $\mu$m data. We find that the magnetic fields derived from optical and Planck agree with each other. The derived magnetic fields are aligned along the observed emission of each cloud as seen in Herschel 250 $\mu$m data. We also find that the relative orientation between the cores and the magnetic fields is random. This lack of correlation may arise due to the fact that the core orientation could also be influenced by the different magnetization within individual clouds at higher densities or the feedback effects which may vary from cloud to cloud. The estimated magnetic field strength and the mass-to-flux ratio suggest that all the clouds are in a magnetically critical state except L1333, L1521E, and L183, where the cloud envelope could be strongly supported by the magnetic field lines.

Observations of interstellar linear polarization in the spectral range 0.35-2.2??m are presented for several stars reddened by dust in the Taurus region. Combined with a previously published study by Whittet et al., these results represent the most comprehensive data set available on the spectral dependence of interstellar polarization in this nearby dark cloud (a total of 27 sight lines). Extinction data for these and other reddened stars in Taurus are assembled for the same spectral range, combining published photometry and spectral classifications with photometry from the Two Micron All Sky Survey. The polarization and extinction curves are characterized in terms of the parameters ?max (the wavelength of maximum polarization) and RV (the ratio of total to selective extinction), respectively. The data are used to investigate in detail the question of whether the optical properties of the dust change systematically as a function of environment, considering stars observed through progressively more opaque (and thus progressively denser) regions of the cloud. At low visual extinctions (0 3, real changes in grain properties occur, characterized by observed RV values in the range 3.5-4.0. A simple model for the development of RV with AV suggests that RV may approach values of 4.5 or more in the densest regions of the cloud. The transition between normal extinction and dense cloud extinction occurs at AV ~ 3.2, a value coincident with the threshold extinction above which H2O-ice is detected on grains within the cloud. Changes in RV are thus either a direct consequence of mantle growth or occur under closely similar physical conditions. Dust in Taurus appears to be in a different evolutionary state compared with other nearby dark clouds, such as ? Oph, in which coagulation is the dominant physical process.