Dust Absorption Research Articles

The physics of Lyman-α escape from disc-like galaxies

ABSTRACT Hydrogen emission lines can provide extensive information about star-forming galaxies in both the local and high-redshift Universe. We present a detailed Lyman continuum (LyC), Lyman-α (Lyα), and Balmer line (Hα and Hβ) radiative transfer study of a high-resolution isolated Milky Way simulation using the state-of-the-art Arepo-RT radiation hydrodynamics code with the SMUGGLE galaxy formation model. The realistic framework includes stellar feedback, non-equilibrium thermochemistry accounting for molecular hydrogen, and dust grain evolution in the interstellar medium (ISM). We extend our publicly available Cosmic Lyα Transfer (COLT) code with photoionization equilibrium Monte Carlo radiative transfer and various methodology improvements for self-consistent end-to-end (non-)resonant line predictions. Accurate LyC reprocessing to recombination emission requires modelling pre-absorption by dust ($f_\text{abs} \approx 27.5\,\rm{per\,\,cent}$), helium ionization ($f_\text{He} \approx 8.7\,\rm{per\,\,cent}$), and anisotropic escape fractions ($f_\text{esc} \approx 7.9\,\rm{per\,\,cent}$), as these reduce the available budget for hydrogen line emission ($f_\text{H} \approx 55.9\,\rm{per\,\,cent}$). We investigate the role of the multiphase dusty ISM, disc geometry, gas kinematics, and star formation activity in governing the physics of emission and escape, focusing on the time variability, gas-phase structure, and spatial spectral, and viewing angle dependence of the emergent photons. Isolated disc simulations are well-suited for comprehensive observational comparisons with local Hα surveys, but would require a proper cosmological circumgalactic medium (CGM) environment as well as less dust absorption and rotational broadening to serve as analogs for high-redshift Lyα emitting galaxies. Future applications of our framework to next-generation cosmological simulations of galaxy formation including radiation-hydrodynamics that resolve ≲10 pc multiphase ISM and ≲1 kpc CGM structures will provide crucial insights and predictions for current and upcoming Lyα observations.

Methodology for substantiating the effectiveness of dust capture by “green” roofs

Introduction. The analysis of practical and theoretical experience shows a significant impact of “green” roofs to reduce the concentration of PM2.5, but the existing methods do not allow in calculating the concentration of pollutants to take into account the dust absorption capacity of the plantations in respect of PM2.5 particles. The aim of this work is to create a method to justify the effectiveness of “green” roofs to reduce fine PM2.5 particles to increase the environmental safety of the urban environment (as applied to the RF) according to the proposed typology based on the developed mathematical model.
 
 Materials and methods. Analytical generalization and systematization of scientific research, mathematical methods were applied.
 
 Results. The developed method represents a sequence of 29 actions, the implementation of which will lead to a conclusion about whether to green the existing building roof, and whether it will be effective in terms of reducing the concentration of fine particles PM2.5 in the air environment. Performing the actions involves performing a calculation in accordance with a mathematical model. The final numerical result of this methodology will be the average for the summer period of time daily accumulation of dust on the surface of the “green” roof in grams. The greater the value, the more effective the device “green” roof in the selected location in terms of improving the environmental safety of the city.
 
 Conclusions. The developed method has practical significance and can be used in various urban planning scenarios, when it is necessary to evaluate numerically the effectiveness of the “green” roof on a particular building, which is carried out at the design stage by comparing different options for placement of “green” roofs and choose the best of them (for which, other things being equal, the average daily dust accumulation PM2.5 for the summer period in grams on the surface of the “green” roof will be the greatest) in terms of ensuring environmental safety.

Methods for calculating the pollutants dispersion in the urban atmosphere

Introduction. The important peculiarity of urban ecology is air dusting with pollutants PM2.5 formed in traffic dangerous for health of city-dwellers. The work aim is the comparative analysis of methods and techniques of pollutants dispersion calculation (in general and as applied to PM2.5) in the city atmosphere, based on the Gaussian models, simulation models, models with partial derivative equations and statistical models.
 Materials and methods. Analytical generalization and systematization of the experience of domestic and foreign studies set forth in the research literature were applied.
 Results. Comparative analysis showed that most of the reviewed methods and techniques in the calculation of the pollutants dispersion takes into account only the parameters of the pollution source, which makes it possible to choose the correct location and capacity. However, for all the merits of all the methods and techniques do not take into account landscaping within the city, which according to recent research has a significant impact on reducing urban air pollution, including in relation to particles PM2.5.
 Conclusions. The next step towards the development of calculation methods and techniques for the dispersion of pollutants in the urban atmosphere in order to ensure the environmental safety of the urban environment is the development of a methodology that allows for the calculation of the concentration of pollutants to take into account the dust absorption capacity of plantings with respect to PM2.5 particles and sorption properties of the deciduous surface of trees and shrubs in the study area. This technique can determine the placement of landscaping objects (trees, shrubs), lawn urban landscaping and landscaping of roofs and stylobates of residential and public buildings in order to reduce PM2.5.

Global Dust Cycle and Direct Radiative Effect in E3SM Version 1: Impact of Increasing Model Resolution

AbstractQuantification of dust aerosols in Earth System Models (ESMs) has important implications for water cycle and biogeochemistry studies. This study examines the global life cycle and direct radiative effects (DREs) of dust in the U.S. Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1), and the impact of increasing model resolution both horizontally and vertically. The default 1° E3SMv1 captures the spatial and temporal variability in the observed dust aerosol optical depth (DAOD) reasonably well, but overpredicts dust absorption in the shortwave (SW). Simulations underestimate the dust vertical and long‐range transport, compared with the satellite dust extinction profiles. After updating dust refractive indices and correcting for a bias in partitioning size‐segregated emissions, both SW cooling and longwave (LW) warming of dust simulated by E3SMv1 are increased and agree better with other recent studies. The estimated net dust DRE of −0.42 Wm−2 represents a stronger cooling effect than the observationally based estimate −0.2 Wm−2 (−0.48 to +0.2), due to a smaller LW warming. Constrained by a global mean DAOD, model sensitivity studies of increasing horizontal and vertical resolution show strong influences on the simulated global dust burden and lifetime primarily through the change of dust dry deposition rate; there are also remarkable differences in simulated spatial distributions of DAOD, DRE, and deposition fluxes. Thus, constraining the global DAOD is insufficient for accurate representation of dust climate effects, especially in transitioning to higher‐ or variable‐resolution ESMs. Better observational constraints of dust vertical profiles, dry deposition, size, and LW properties are needed.

Distribution characteristics of an airflow–dust mixture and quantitative analysis of the dust absorption effect during tunnel sub-regional coal cutting

Optimizing the tunnel ventilation scheme is one of the main ways to achieve safe production in coal mines. Based on the actual production situation, computational fluid dynamics technology was used to study the distribution characteristics of an airflow–dust mixture for different air-absorption volumes (Qe) of the ventilation system during sub-regional coal cutting. According to the dust concentration values registered at different locations, the entropy weight method was applied to quantitatively analyze the dust absorption effect of the fan. The research results showed that: the dust distribution was jointly affected by the cutting unit and the completed cutting zone; moreover, the dust control effect was better in the middle cutting zones than in the others. Under the ventilation system, the overall distribution of dust in the tunnel could be roughly divided into three sections: the dust removal section (I), the dust blocking section (II), and the gentle section (III). The optimal Qe (575 m3/min) was determined based on the weight of the different zones. Finally, the entropy weight method was applied for determining the ideal mine ventilation system scheme and, hence, improve safety production in coal mines during sub-regional cutting dust production.

Real-time measurements of mineral dust concentration in coarse particulate matter (PM10–2.5) by employing a novel optical-based technique in Los Angeles

As a primary component of coarse particulate matter (PM), ambient mineral dust has been linked to adverse health effects. Los Angeles, the largest metropolitan urban area of the United States, is impacted by both windblown and localized sources of mineral dust, often internally mixed with black carbon. The estimation of mineral dust concentrations with a high time resolution becomes critical in improving our understanding of its sources and temporal trends. Using Aethalometers combined with a high-volume virtual impactor (VI) to enrich coarse (2.5 <dp < 10 μm) particles, the light absorption and mass concentration of mineral dust were estimated in real-time during summer, fall, and winter over 2020–2021. The concentration-enriched coarse PM was collected on Teflon filters, and its chemical composition in terms of trace elements and metals was chemically quantified. The high time-resolution measurements enabled us to calculate the absorption coefficient of enriched dust particles by subtracting the light absorption of the post-VI coarse PM from that of the PM2.5 aerosol fraction to reduce the impact of stronger light absorbers in ambient PM. Mineral dust was more prevalent during the fall and winter campaigns (i.e., 19.3 and 11.4 μg/m3, respectively), lower concentrations were observed during the summer campaign (i.e., 8.50 μg/m3). The calculated absorption Ångström exponent (AAE) was 2.18, highlighting the presence of dust particles during the sampling period. The dust mass absorption coefficient was estimated to be 2.7 ± 1.6 Mm−1 at 370 nm and 0.41 ± 0.16 Mm−1 at 880 nm wavelengths, respectively. The validation of the proposed approach was investigated by comparing the evaluated mineral dust mass concentrations in this study with the reported coarse PM concentrations by the California Air Resources Board (CARB). The results reported by the optical-based approach with high temporal resolution can provide crucial information on identifying sources of mineral dust in urban areas.

Hαemission in local galaxies: star formation, time variability, and the diffuse ionized gas

ABSTRACTThe nebular recombination line H α is widely used as a star formation rate (SFR) indicator in the local and high-redshift Universe. We present a detailed H α radiative transfer study of high-resolution isolated Milky-Way and Large Magellanic Cloud simulations that include radiative transfer, non-equilibrium thermochemistry, and dust evolution. We focus on the spatial morphology and temporal variability of the H α emission, and its connection to the underlying gas and star formation properties. The H α and H β radial and vertical surface brightness profiles are in excellent agreement with observations of nearby galaxies. We find that the fraction of H α emission from collisional excitation amounts to fcol ∼ 5–$10{{\ \rm per\ cent}}$, only weakly dependent on radius and vertical height, and that scattering boosts the H α luminosity by $\sim 40{{\ \rm per\ cent}}$. The dust correction via the Balmer decrement works well (intrinsic H α emission recoverable within 25 per cent), though the dust attenuation law depends on the amount of attenuation itself both on spatially resolved and integrated scales. Important for the understanding of the H α–SFR connection is the dust and helium absorption of ionizing radiation (Lyman continuum [LyC] photons), which are about $f_{\rm abs}\approx 28{{\ \rm per\ cent}}$ and $f_{\rm He}\approx 9{{\ \rm per\ cent}}$, respectively. Together with an escape fraction of $f_{\rm esc}\approx 6{{\ \rm per\ cent}}$, this reduces the available budget for hydrogen line emission by nearly half ($f_{\rm H}\approx 57{{\ \rm per\ cent}}$). We discuss the impact of the diffuse ionized gas, showing – among other things – that the extraplanar H α emission is powered by LyC photons escaping the disc. Future applications of this framework to cosmological (zoom-in) simulations will assist in the interpretation of spectroscopy of high-redshift galaxies with the upcoming James Webb Space Telescope.

Numerical Simulation Study on Dust Suppression Mechanism of Burning Rock Blasting in Open-Pit Mine

In an open-pit mine in Xinjiang, part of the stripped area is covered by burnt rock. Due to the low strength and fragility of burnt rock, dust is more easily generated during blasting. Taking the mining area as the research background, the mechanical property parameters of burnt rock were tested, and the blasting parameter design of on-site operation was understood. The blasting numerical simulation of burnt rock step was carried out by using a numerical simulation software (LS-DYNA). From the angle of stress on rock, the stress cloud and stress curve of numerical simulation are analyzed, and it is concluded that the fundamental reason for the large dust production in blasting operation is that the burnt rock is crushed excessively after the action of explosion wave, and the explosive energy is too large, which is converted into kinetic energy to drive the dust to escape. In order to improve the utilization rate of explosives and reduce the output of blasting dust, the original blasting parameters were optimized as 8-m hole spacing, 6.5-m row spacing, 0.21-kg/m³ unit explosive consumption, 1-m interval charge, and 55-ms short-delay blasting through numerical simulation and orthogonal experiment. In the mining area, the measures of dustproof and dust reduction by blasting protection blanket and dust absorption cotton are adopted. Combined with the optimized blasting parameters, the field test proves that the dust removal efficiency is up to 82.4%.

First Images of the Molecular Gas around a Born-again Star Revealed by ALMA

Abstract Born-again stars allow probing stellar evolution in human timescales and provide the most promising path for the formation of hydrogen-deficient post-asymptotic giant branch objects, but their cold and molecular components remain poorly explored. Here we present ALMA observations of V 605 Aql that unveil for the first time the spatio-kinematic distribution of the molecular material associated with a born-again star. Both the continuum and molecular line emission exhibit a clumpy ring-like structure with a total extent of ≈1″ in diameter. The bulk of the molecular emission is interpreted as being produced in a radially expanding disk-like structure with an expansion velocity v exp ∼ 90 km s−1 and an inclination i ≈ 60° with respect to the line of sight. The observations also reveal a compact high-velocity component, v exp ∼ 280 km s−1, that is aligned perpendicularly to the expanding disk. This component is interpreted as a bipolar outflow with a kinematical age τ ≲ 20 yr, which could either be material that is currently being ejected from V 605 Aql, or is being dragged from the inner parts of the disk by a stellar wind. The dust mass of the disk is in the range M dust ∼ 0.2–8 × 10−3 M ⊙, depending on the dust absorption coefficient. The mass of the CO is M CO ≈ 1.1 × 10−5 M ⊙, which is more than three orders of magnitude larger than the mass of the other detected molecules. We estimate a 12C/13C ratio of 5.6 ± 0.6, which is consistent with the single stellar evolution scenario in which the star experienced a very late thermal pulse instead of a nova-like event as previously suggested.

ОЦІНКА ЯКІСНОЇ І КІЛЬКІСНОЇ ХАРАКТЕРИСТИКИ ЗЕЛЕНИХ НАСАДЖЕНЬ НА ТЕРИТОРІЇ ДИТЯЧИХ МАЙДАНЧИКІВ М. ХАРКІВ

Purpose. To analyze the condition of green spaces on playgrounds in urbanized areas, with the example of Kharkiv, to predict the effectiveness of their dust, noise and gas absorption functions, as greenery is the most accessible and versatile way of protection in urban environments. Methodology. We conducted research on 540 playgrounds with 6627 trees and shrubs, representing 59 species, of which 37 are major. Qualitative analysis was carried out by dividing into groups according to height, age, resistance to high and low temperatures, and we also assessed the sanitary condition of tree and shrub vegetation. We divided the weakened greenery into groups according to the type of damage. Results. The data obtained indicate that most plants are resistant to both low and high temperatures. Only half of the studied objects can be classified as healthy plants, respectively, only this part of the plants is able to effectively perform the protective function. About 46,9% of the surveyed greenery is exposed to mechanical damage, fungal damage, some plants are affected by insects or diseases. Mechanical damage is one of the main causes of weakening of plants in the urban environment, which is associated with the work of municipal services, building works. In addition, children deliberately break and damage the branches of trees and shrubs on playgrounds. The greatest degree of damage by caterpillars and leafminer is characteristic of Fraxinus excelsior L., Morus nigra L.. Leaf spotting was quite common in Betula pendula Roth., Salix acutifolia Willd., Salix babylonica L., Tilia cordata Mill. and others. Powdery mildew was found on young shoots and leaves of Betula, Acer, Ulmus, Fraxinus, and Salix. Necroses and stem rot were not often observed. We have developed a list of recommendations to improve the condition of green areas in playgrounds. Originality. For the first time, we analysed the condition of green areas at children's playgrounds and proposed recommendations for improving their condition. Practical value. The findings can be used in evaluating the effectiveness of the protective functions of green spaces in large cities. References 17, tables 7, figures 2.

Experimental Research of Fibrous Materials for Two-Stage Filtration of the Intake Air of Internal Combustion Engines.

Pollutant properties in intake air to internal combustion engines were analyzed. Mineral dust particles’ influence on accelerated engine components’ wear was discussed. Dust concentration values in the air under various operating conditions in trucks and special vehicles were presented. The idea and necessity for using two-stage filters, operating in a “multi-cyclone–porous partition” system for vehicles operated in dusty air conditions, are presented. Information from the literature information has been presented, showing that impurities in small grain sizes reduce fiber bed absorbency. It has been shown that such a phenomenon occurs during filter material operation, located directly behind the inertial filter (multi-cyclone), which off-road vehicles are equipped with. It results in a greater pressure drop intensity increase and a shorter proper filter operation period. It has been shown that filter material selection for the motor vehicle air filter requires knowledge of the mass of stopped dust per filtration unit area (dust absorption coefficient km) determined for a given permissible resistance value Δpfdop. It has been shown that there is no information on absorption coefficient values for filter materials operating in a two-stage “multi-cyclone–porous partition” separation system. Original methodology and conditions for determining dust absorption coefficient (km) of a separation partition, operating under the conditions of two-stage filtration, were presented. The following characteristics were tested: separation efficiency, filtration performance, and pressure drop characteristics of three different filtration partitions. These were A (cellulose), B (cellulose and polyester), and C (cellulose, polyester, and nanofibers layer), working individually and in a two-stage system—behind the cyclone. Granulometric dust composition dosed into the cyclone and cyclone downstream was determined. During tests, conditions corresponding to air filter’s actual operating conditions, including separation speed and dust concentration in the air, were maintained. For the pressure drop values, the dust absorption coefficient (km) values of three different filtration partitions (A, B, and C), working individually and in a two-stage system—behind the cyclone—were determined experimentally.

Direct Radiative Effects in Haboobs

AbstractConvective dust storms, or haboobs, form when strong surface winds loft loose soils in convective storm outflow boundaries. Haboobs are a public safety hazard and can cause a near instantaneous loss of visibility, inimical air quality, and contribute significantly to regional dust and radiation budgets. Nevertheless, reliable predictions of convective dust events are inhibited by a lack of understanding regarding the complex and non‐linear interactions between density currents, or convective cold pools, and dust radiative effects. In this study, the Weather Research and Forecasting model coupled with Chemistry (WRF‐Chem) is utilized to simulate the effect dust radiation interactions have on a long‐lived haboob case study that spans three distinct radiative regimes: day (high shortwave), evening (low shortwave), and night [longwave (LW) only]. A sophisticated algorithm is used to track and identify the numerous convective old pool boundaries in the simulations and assemble statistics that represent the impact of dust radiative effects. To first order, dust scattering of shortwave radiation in the day leads to a colder, dustier, and faster moving convective cold pool. In the transition period of early evening, the shortwave effects diminish while LW dust absorption leads to warmer, slower density currents that loft less dust as they propagate. At night, the haboob is again warmer due to dust absorption, but gustier in the more stable nocturnal surface layer, leading to enhanced dust emissions.

The southern hemisphere narrow-line seyfert 1 infrared survey

ABSTRACT We present a near-infrared spectroscopic survey of narrow-line Seyfert 1 galaxies in the Southern hemisphere (using the SOFI instrument on the ESO-NTT telescope), sampled from optical surveys. We examine the kinematics of the broad-line region (BLR), probed by the emission line width of hydrogen (Pa α and H β). We observed 57 objects, of which we could firmly measure Pa α in 49 cases. We find that a single Lorentzian fit (preferred on theoretical grounds) is preferred over multicomponent Gaussian fits to the line profiles; a lack of narrow-line region emission, overwhelmed by the pole-on view of the BLR light, supports this. We recompute the catalogue black hole (BH) mass estimates, using the values of full width half-maximum and luminosity of H β, both from catalogue values and re-fitted Lorentzian values. We find a relationship slope greater than unity compared to the catalogue values. We ascribe this to contamination by galactic light or difficulties with line flux measurements. However, the comparison of masses computed by the fitted Lorentzian and Gaussian measurements show a slope close to unity. Comparing the BH masses estimated from both Pa α and H β, the line widths and fluxes shows deviations from expected; in general, however, the computed BH masses are comparable. We posit a scenario where an intermixture of dusty and dust-free clouds (or alternately a structured atmosphere) differentially absorbs the line radiation of the BLR, due to dust absorption and hydrogen bound-free absorption.

Hoyle–Lyttleton accretion on to black hole accretion disks with super-Eddington luminosity for dusty gas

Abstract We investigate the Hoyle–Lyttleton accretion of dusty gas for the case where the central source is the black hole accretion disk. By solving the equation of motion taking into account the radiation force which is attenuated by the dust absorption, we reveal the steady structure of the flow around the central object. We find that the mass accretion rate tends to increase with an increase of the optical thickness of the flow and the gas can accrete even if the disk luminosity exceeds the Eddington luminosity for the dusty gas, since the radiation force is weakened by the attenuation via the dust absorption. When the gas flows in from the direction of the rotation axis for the disk with Γ′ = 3.0, the accretion rate is about $93\%$ of the Hoyle–Lyttleton accretion rate if τHL = 3.3 and zero for τHL = 1.0, where Γ′ is the Eddington ratio for the dusty gas and τHL is the typical optical thickness of the Hoyle–Lyttleton radius. Since the radiation flux in the direction of disk plane is small, the radiation force tends not to prevent gas accretion from the direction near the disk plane. For τHL = 3.3 and Γ′ = 3.4, although the accretion is impossible in the case of Θ = 0°, the accretion rate is $28\%$ of the Hoyle–Lyttleton one in the case of Θ = 90°, where Θ is the angle between the direction the gas is coming from and the rotation axis of the disk. We also obtain relatively high accretion luminosity that is realized when the accretion rate of the disk on to the BH is consistent with that via the Hoyle–Lyttleton mechanism taking into account the effect of radiation. This implies that the intermediate-mass black holes moving in the dense dusty gas are identified as luminous objects in the infrared band.

A Machine Learning Approach to Objective Identification of Dust in Satellite Imagery

AbstractAirborne dust has broad adverse effects on human activity, including aviation, human health, and agriculture. Remote sensing observations are used to detect dust and aerosols in the atmosphere using long established techniques. False color Red‐Green‐Blue (RGB) imagery using band differences sensitive to dust absorption (Dust RGB) is currently used operationally to assist forecasters and decision‐makers in identifying dust at night, but there are still limitations, subjectivity, and nuances to image interpretation making night‐time dust identification difficult even for experts. This study applies machine learning to the problem of night‐time dust detection with a simple random forest (RF) model using Geostationary Operational Environmental Satellite‐16 (GOES‐16) Advanced Baseline Imager (ABI) infrared imagery, band differences sensitive to dust absorption, and Dust RGB color components as inputs to the model. The RF model achieves an Area‐Under‐Curve (AUC) of 0.97 with a standard deviation of 0.04 for dust cases. For images with dust present, the model correctly labels 85% of dust pixels and 99.96% of no‐dust pixels for all dust images in the validation data set. The addition of a single null case to the training data set drastically reduces error in labeling no‐dust pixels as dust from 45% to 14.5%. Application of the machine learning model to the April 13–14, 2019 dust event demonstrates the ability of the model to identify dust during night‐time hours when visual dust detection is limited by the cooling ground surface characteristics.

Impact of Dust on Spectral Distortion Measurements of the Cosmic Microwave Background

Abstract Spectral distortions of the cosmic microwave background (CMB) are sensitive to energy injection by exotic physics in the early universe. The proposed Primordial Inflation Explorer (PIXIE) mission has the raw sensitivity to provide meaningful limits on new physics, but only if foreground emission can be adequately modeled. We quantify the impact of interstellar dust on Compton y and μ measurements by considering a range of grain size distributions and compositions constrained by theoretical and observational priors. We find that PIXIE can marginalize over a modest number of dust parameters and still recover y and μ estimates, though with increased uncertainty. As more foreground components are included (synchrotron, free–free), estimates of y degrade, and measurement of μ in the range sometimes considered for the standard ΛCDM of 2 × 10−8 becomes infeasible without ancillary low-frequency foreground information. An additional concern is dust absorption of the CMB monopole, a subtle effect that must be included. We quantify one form of model discrepancy error, finding that the error introduced by fitting our interstellar medium dust model with a modified blackbody is too large for CMB spectral distortions to be detectable. The greatest challenge may be the cosmic infrared background (CIB). We find that μ and y are extremely sensitive to modeling choices for the CIB, and quantify biases expected for a range of assumptions.

Impact of hematite on dust absorption at wavelengths ranging from 0.2 to 1.0 µm: an evaluation of literature data using the T-matrix method.

Hematite is the absorbing mineral component of dust aerosols in the shortwave spectral region. However, dust shortwave absorption related to hematite suffers from significant uncertainties. In this study, we evaluated available hematite complex refractive index data in the literature on determining the dust effective refractive index at wavelengths ranging from 0.2 to 1.0 µm using rigorous T-matrix methods. Both spherical and super-spheroidal dust with hematite inclusions were examined to compute the dust optical properties and associated effective refractive indices. We found that the imaginary part of the effective refractive index retrieved from all available hematite complex refractive index data is larger than the measured effective values from Di Biagio et al. [Atmos. Chem. Phys.19, 15503, (2019)10.5194/acp-19-15503-2019]. The result obtained using the hematite refractive index from Hsu and Matijevic [Appl. Opt.241623 (1985)10.1364/AO.24.001623] is closest to but approximately two times larger than Di Biagio et al. [Atmos. Chem. Phys.19, 15503, (2019)10.5194/acp-19-15503-2019]. Our results emphasize the importance of accurate measurements of mineral refractive indices to clarify the dust absorption enigma.

The tidal stream generated by the globular cluster NGC 3201

ABSTRACT We detect a tidal stream generated by the globular cluster NGC 3201 extending over ∼140 deg on the sky, using the Gaia DR2 data, with the maximum-likelihood method we presented previously to study the M68 tidal stream. Most of the detected stream is the trailing one, which stretches in the southern Galactic hemisphere and passes within a close distance of 3.2 kpc from the Sun, therefore making the stream highly favourable for discovering relatively bright member stars, while the leading arm is further from us and behind a disc foreground that is harder to separate from. The cluster has just crossed the Galactic disc and is now in the northern Galactic hemisphere, moderately obscured by dust, and the part of the trailing tail closest to the cluster is highly obscured behind the plane. We obtain a best-fitting model of the stream which is consistent with the measured proper motion, radial velocity, and distance to NGC 3201, and show it to be the same as the previously detected Gjöll stream by Ibata et al. We identify ∼200 stars with the highest likelihood of being stream members using only their Gaia kinematic data. Most of these stars (170) are photometrically consistent with being members of NGC 3201 when they are compared to the cluster H–R diagram, only once a correction for dust absorption and reddening by the Galaxy is applied. The remaining stars are consistent with being random foreground objects according to simulated data sets. We list these 170 highly likely stream member stars.

STUDY OF THE INFLUENCE OF CONSTRUCTION AND MODE PARAMETERS ON THE HYDRODYNAMICS OF A HOLLOW VORTEX APPARATUS

The research was to determine the more efficient design of the swirler from the point of view of hydrodynamics and heat and its optimal parameters. Various swirl designs were manufactured and tested. After preliminary studies conducted on a laboratory installation with a glass working apparatus, several swirlers were selected taking into account their hydraulic resistance, the structure of the swirling gas-liquid flow, and the amount of liquid entrainment by gas. The results of an experimental study of the hydrodynamics of a hollow vortex apparatus with one and two tangential and axial swirlers. Hydraulic losses in the channel and in the swirls during the direct downward movement of gas and gas-liquid flow are determined. In addition, studies of the hydraulic resistance of a vortex-type device allow us to determine the energy consumption of this device for conducting complex processes of dust collection and absorption or contact heat exchange. The hydraulic resistance in the presence of a liquid film is higher than in the case of a single-phase gas flow. The pressure drop in the studied vortex apparatus does not exceed the resistance of high-performance cyclones and vortex-type devices of other designs. The effect of the twist coefficient of gas swirlers, gas velocity, and liquid flow on the pressure drop in the vortex apparatus is established

The VANDELS survey: The relation between the UV continuum slope and stellar metallicity in star-forming galaxies at z ∼ 3

The estimate of stellar metallicities (Z*) of high-z galaxies are of paramount importance in order to understand the complexity of dust effects and the reciprocal interrelations among stellar mass, dust attenuation, stellar age, and metallicity. Benefiting from uniquely deep far-UV spectra of &gt; 500 star-forming galaxies at redshifts 2 &lt; z &lt; 5 extracted from the VANDELS survey and stacked in bins of stellar mass (M*) and UV continuum slope (β), we estimate their stellar metallicities Z* from stellar photospheric absorption features at 1501 and 1719 Å, which are calibrated with Starburst99 models and are largely unaffected by stellar age, dust, IMF, nebular continuum, or interstellar absorption. Comparing them to photometric-based spectral slopes in the 1250–1750 Å range, we find that the stellar metallicity increases by ∼0.5 dex from β ∼ −2 to β ∼ −1 (1 ≲ A1600 ≲ 3.2), and a dependence with β holds at fixed UV absolute luminosity MUV and stellar mass up to ∼109.65 M⊙. As a result, metallicity is a fundamental ingredient for properly rescaling dust corrections based on MUV and M*. Using the same absorption features, we analyzed the mass-metallicity relation (MZR), and find it to be consistent with the previous VANDELS estimation based on a global fit of the FUV spectra. Similarly, we do not find a significant evolution between z ∼ 2 and z ∼ 3.5. Finally, the slopes of our MZR and Z* − β relation are in agreement with the predictions of well-studied semi-analytic models (SAM) of galaxy formation, while some tensions remain concerning the absolute metallicity normalization. The relation between the UV slope and stellar metallicity is fundamental to the exploitation of large volume surveys with next-generation telescopes and for the physical characterization of galaxies in the first billion years of our Universe.