Dust Formation Mechanism Research Articles

Tungsten Molecular Species in Deuterium Plasmas in Contact with Sputtered W Surfaces.

We show that in plasmas generated in deuterium in the presence of sputtered W surfaces, various molecular tungsten species are formed, whose chemical composition depends on the presence of gaseous impurities, namely, nitrogen, oxygen, and hydrogen. A magnetron discharge was used for plasma sustaining, and the species were investigated by mass spectrometry and optical emission spectroscopy. The identified tungsten-containing molecules are described by the chemical formula WOxNyDzHt, where x = 0-4, y = 0-3, z = 0-3, t = 0-5. Presumptively, even higher mass tungsten molecular species are present in plasma, which were not detected because of the limitation of the spectrometer measurement range to 300 amu. The presence of these molecules will likely impact the W particle balance and dust formation mechanisms in fusion plasmas.

Экспериментальное исследование накопления углеродных отложений в кислородно-метановом модельном газовом тракте

The paper considers mechanisms of the carbon deposits formation on the metal surface at contact with the gas phase containing products of incomplete combustion of the oxygen-methane generator gas. The first mechanism is the socalled mechanism of metal dust formation, which products remain on the wall surface and form the carbon deposits, the second is the mechanism of carbon deposits formation associated with the carbon particles in the gas flow, which are being deposited on the wall. An experimental system was developed with the working section being a model path of the oxygen-methane generator gas of the reducing composition; and accumulation of the carbon deposits was experimentally studied. When selecting performance characteristics of the experimental system, features of the liquid rocket engine gas path were taken into account; therefor, the experimental system was having characteristics closer to the expected characteristics of the full-scale gas path. Intensities of the deposit formation on samples of metallic material and reference quartz were compared. It was established that the main mechanism for the carbon deposits formation was precipitation of soot contained in the generator gas flow onto the wall of the gas path. The number of deposits was determined by weight. The range of the fuel components ratio was identified, where formation of the deposits was minimal

Обеспечение безопасности при внедрении новых технологий в проходческих и очистных забоях

Introduction. New technologies and high-capacity equipment provide the intensification of technological processes in drifting and working faces that leads to changes of dust and aerodynamic processes that as a rule are not able to emphasize modern methods of explosion safety control in coal mines. Thus the process of introducing new technologies faces a number of features that require the development of new approaches of solving the safe mining issues in practice. One of these issues is the significant amount of organic aerosol formation, that is not measured by modern methods of explosion safety control in coal mines, but its presence in a methane-air environment can significantly shift the ignition threshold and significantly increase the rate of pressure rise during an explosion. Research methods and materials. Authors method of determination level of dust formation with special devices consisting of two filters placed vertically and horizontally in special well-room and distributed in several mine workings profile perimeter contours is proposed. Research results. As a solution the authors proposed a method for the rapid determination of the level of deposited dust in the mine workings that allows to prevent its possible explosion. Also schemes of special devices placement for measuring the level of dust formation at the sides of the mine workings are given. Using the prototype of multifunctional mechanized walking support developed by the authors in combination with high-performance combines the risks arising from the introduction of technologies for high-speed spilling of underground mining and mining of difficult coal reserves are demonstrated. The assessment of mining-geological and technological risks of stopping the technological process during the introduction of new technologies was made, a method of assessment the components that impact the risk of explosion of a dust-methane-air mixture in mine workings was developed. Discussion. Based on the identified risks of stopping the technological process the authors recommend taking into account technological aspects that may lead to accidents or incidents related both to the design feature of new types of high-performance equipment and to the sequence and duration of the stages of the main technological processes of disintegration and transportation of the recaptured rock mass. Conclusion. Interval of performing events of making mine workings safe is determined for preventing risks of explosion of a dust-methane-air mixture during coal-face work with high-performance equipment based on author’s methods of measuring determination level of dust formation Resume. As a result it is concluded that the effective introduction of new technological processes is impossible without accurate and operational control of the dust formation level in mine workings that is especially important with constantly increasing pounding on drifting and working faces. However, the experience of practical testing the authors method shows that it is necessary to investigate an additional research of the mechanism of dust formation and its nanoscale component for a reliable assessment of the coal dust explosive index and its influence to ignition process and risks of explosion of a dust-methane-air mixture.

Dust Production in a Thin Dense Shell in Supernovae with Early Circumstellar Interactions

In supernovae (SNe), where the light curves show evidence of strong and early interaction between the ejecta and the circumstellar matter (CSM), the formation of new dust is estimated to take place in a dense shell of gas between the forward shock (FS) and the reverse shock (RS). For the first time, in this study the mechanism of dust formation in this dense shell is modeled. A set of nine cases, considering variations of the ejecta mass and the pre-explosion mass-loss rates, is considered, accounting for the diverse nature of interactions reported in such SNe. For a single main-sequence mass, the variation of ejecta mass was manifested as a variation of the H-shell mass of the star, lost due to pre-explosion mass loss. We find that the dust masses in the dense shell range between 10−3 and 0.8 M ⊙, composed of O-rich and C-rich grains, whose relative proportions are determined by the nature of interaction. Dust formation in the post-shock gas is characterized by a gradual production rate, mostly ranging from 10−6 to 10−3 M ⊙ day−1, which may continue for a decade, post-explosion. A higher mass-loss rate leads to a larger mass of dust, while a smaller ejecta mass (smaller leftover H shell) increases the efficiency of dust production in such SNe. Dust formed behind the RS, as in our calculations, is not subject to destruction by either the FS or RS and is thus likely to survive in a larger proportion than dust formed in the ejecta.

Cross machine investigation of magnetic tokamak dust; structural and magnetic analysis

Magnetic dust collected from multiple fusion devices (FTU, Alcator C-Mod, COMPASS) that feature different plasma-facing components (PFCs) and toroidal magnetic fields has been analyzed by means of the X-ray diffraction technique aiming to investigate the nature and origin of dust magnetism. Analysis led to the conclusion that the main mechanism of ferromagnetic dust formation is the change of iron crystalline phase from austenitic to ferritic during the re-solidification of stainless steel droplets. Analysis also revealed differences in the collected dust structure and an unexpectedly high amount of stainless steel based dust in its native austenitic phase. Theoretical estimates showed that the magnetic moment force can also mobilize strongly paramagnetic adhered dust prior to the establishment of proper tokamak discharges. The post-mortem analysis of dust collected during pure magnetic discharges in FTU confirmed these estimates. • Magnetic dust from various tokamaks was analyzed by means of X-ray diffraction. • Magnetic dust was collected from FTU during pure magnetic discharges. • The ferromagnetism of SS dust stems from the austenite to ferrite phase change. • Strongly paramagnetic SS dust can also be mobilized by the magnetic moment force. • Magnetized dust could be an issue during start-up phases in future fusion devices.

The inner dust shell of Betelgeuse detected by polarimetric aperture-masking interferometry

Context. Theory surrounding the origin of the dust-laden winds from evolved stars remains mired in controversy. Characterizing the formation loci and the dust distribution within approximately the first stellar radius above the surface is crucial for understanding the physics that underlie the mass-loss phenomenon. Aims. By exploiting interferometric polarimetry, we derive the fundamental parameters that govern the dust structure at the wind base of a red supergiant. Methods. We present near-infrared aperture-masking observations of Betelgeuse in polarimetric mode obtained with the NACO/SAMPol instrument. We used both parametric models and radiative transfer simulations to predict polarimetric differential visibility data and compared them to SPHERE/ZIMPOL measurements. Results. Using a thin dust shell model, we report the discovery of a dust halo that is located at only 0.5 R⋆ above the photosphere (i.e. an inner radius of the dust halo of 1.5 R⋆). By fitting the data under the assumption of Mie scattering, we estimate the grain size and density for various dust species. By extrapolating to the visible wavelengths using radiative transfer simulations, we compare our model with SPHERE/ZIMPOL data and find that models based on dust mixtures that are dominated by forsterite are most favored. Such a close dusty atmosphere has profound implications for the dust formation mechanisms around red supergiants.

Dust production scenarios in galaxies at z ∼6–8.3

Context. The mechanism of dust formation in galaxies at high redshift is still unknown. Asymptotic giant branch (AGB) stars and explosions of supernovae (SNe) are possible dust producers, and non-stellar processes may substantially contribute to dust production, for example grain growth in the interstellar medium. Aims. Our aim is to determine the contribution to dust production of AGB stars and SNe in nine galaxies at z ∼ 6−8.3, for which observations of dust have been recently attempted. Methods. In order to determine the origin of the observed dust we have determined dust yields per AGB star and SN required to explain the total amounts of dust in these galaxies. Results. We find that AGB stars were not able to produce the amounts of dust observed in the galaxies in our sample. In order to explain these dust masses, SNe would have to have maximum efficiency and not destroy the dust which they formed. Conclusions. Therefore, the observed amounts of dust in the galaxies in the early universe were formed either by efficient supernovae or by a non-stellar mechanism, for instance the grain growth in the interstellar medium.

Building blocks of dust: A coordinated laboratory and astronomical study of the archtype AGB carbon star IRC+10216

This article provides an overview of recent astronomical studies and a closely coordinated laboratory program devoted to the study of the physics and chemistry of carbon-rich Asymptotic Giant Branch stars, as illustrated by the archtype star IRC+10216. The increased sensitivity and angular resolution of high altitude, ground-based millimeter-wave interferometers in the past few years has enabled molecular astronomers to determine the excitation and spatial distribution of molecules within a few stellar radii of the central star where the molecular seeds of dust are formed, and thus to critically assess the physicochemical mechanisms of dust formation and growth. However the astronomical studies are crucially dependent on precise laboratory measurements of the rotational spectra — both in the ground and vibrationally excited states of the normal and rare isotopic species as well — of the principal molecules in the inner region which appear to contain only two or three heavy atoms.Much remains to be done by laboratory spectroscopists as evidenced by the large number of unassigned millimeter-wave rotational lines that are observed in the inner envelope of IRC+10216. To assess whether vibrationally excited SiC2 and HCN are the carriers of some of the unassigned features observed in this source, millimeter-wave laboratory spectra are compared with Cycle 0 observations from the Atacama Large Millimeter-wave Array (ALMA) under experimental conditions that produce both species. Also highlighted are ongoing laboratory studies of the silicon carbides SiC2 and SiCSi in their ground and excited vibrational states, and c-SiC3 in its ground vibrational state. Following the initial detection of c-SiC3 and SiCSi in the outer molecular envelope of IRC+10216, the laboratory spectroscopy was extended to higher frequency in support of the recent interferometric measurements. Thirty-two new millimeter-wave rotational transitions of SiCSi with J⩽48,Ka⩽3 and upper level energies Eu⩽484 K in the range from 178 to 391 GHz, and 35 new transitions of c-SiC3 with J⩽38,Ka⩽20 and Eu⩽875 K between 315 and 440 GHz were measured in the laboratory. In addition, five or six rotational transitions in one quanta of each of the three fundamental vibrational modes of SiCSi and the two lowest rotational transitions in the previously unexplored C–C stretching mode (ν1) of SiC2 were measured in the normal and doubly substituted 13C isotopic species. Areas of continued emphasis and the importance of complementary experimental methods and production techniques to detect and assign vibrational transitions are also highlighted.

Dust reddening and extinction curves toward gamma-ray bursts at z > 4

Context. Dust is known to be produced in the envelopes of asymptotic giant branch (AGB) stars, the expanded shells of supernova (SN) remnants, and in situ grain growth within the interstellar medium (ISM), although the corresponding efficiency of each of these dust formation mechanisms at different redshifts remains a topic of debate. During the first Gyr after the Big Bang, it is widely believed that there was not enough time to form AGB stars in high numbers, hence the dust at this epoch is expected to be purely from SNe or subsequent grain growth in the ISM. The time period corresponding to z ~ 5−6 is thus expected to display the transition from SN-only dust to a mixture of both formation channels as is generally recognized at present. Aims. Here we aim to use afterglow observations of gamma-ray bursts (GRBs) at redshifts larger than z > 4 to derive host galaxy dust column densities along their line of sight and to test if a SN-type dust extinction curve is required for some of the bursts. Methods. We performed GRB afterglow observations with the seven-channel Gamma-Ray Optical and Near-infrared Detector (GROND) at the 2.2 m MPI telescope in La Silla, Chile (ESO), and we combined these observations with quasi-simultaneous data gathered with the XRT telescope on board the Swift satellite. Results. We increase the number of measured AV values for GRBs at z > 4 by a factor of ~2–3 and find that, in contrast to samples at mostly lower redshift, all of the GRB afterglows have a visual extinction of AV < 0.5 mag. Analysis of the GROND detection thresholds and results from a Monte Carlo simulation show that although we partly suffer from an observational bias against highly extinguished sight-lines, GRB host galaxies at 4 < z < 6 seem to contain on average less dust than at z ~ 2. Additionally, we find that all of the GRBs can be modeled with locally measured extinction curves and that the SN-like dust extinction curve, as previously found toward GRB 071025, provides a better fit for only two of the afterglow SEDs. However, because of the lack of highly extinguished sight lines and the limited wavelength coverage we cannot distinguish between the different scenarios. For the first time we also report a photometric redshift of zphot = 7.88-0.94+0.75 for GRB 100905A, making it one of the most distant GRBs known to date.

Investigation of rock cutting dust formation and suppression using water jets during mining

Dust suppression is an urgent issue for coal mines because the problem of dust has not been solved effectively, harms the health of miners and is a potentially serious threat to the mine environment and safety. Therefore, an effective method for dust suppression is highly desired. In this work, the formation and suppression of cutting dust are analyzed, and a method for suppressing the cutting dust during the formation process in the crushing zone is discussed. Internal and external water jets are used for dust suppression based on the cutting dust formation mechanism and are examined in rock cutting experiments using a newly developed test-bed. The use of internal water jets reduces the cutting dust concentration by over 90% on average, with no obvious relationship between the dust concentration and the water pressure. The use of external water jets reduces the cutting dust by over 65% on average, with an increasing reduction in dust concentration with increasing water pressure from 5MPa to 20MPa.

Electron angular distributions and attachment rates in o-Benzyne and Phenyl aromatic molecules: the effect of the permanent dipoles

Free, gas-phase polycyclic aromatic hydrocarbons (PAHs) and related species are currently considered to play an important role in the interstellar/circumstellar medium as they are thought to significantly contribute to both Diffuse and Unidentified infrared interstellar bands. They are also considered fundamental blocks of the interstellar dust and several formation mechanisms were proposed with regard to their interstellar/circumstellar synthesis. In this paper we therefore present and discuss the results obtained from ab initio quantum scattering calculations of the response from neutral polar aromatic single-ring species to low-energies electron collisions. Our main purpose is here to provide new values for the rate constants for electron attachment to orthobenzyne and to phenyl molecules by discussing in detail the effects of the long-range dipole interaction in the framework of the Born perturbative approximation at the first order. We shall further discuss the specific behavior of the electrons’ diffusion by such molecules, especially in the low-energy range of the scattered particles’ energies as guided by their permanent dipole moments. We shall also provide accurate numerical fittings for both rates and give explicitly the fitting parameters for their possible use in evolutionary models.

ANOMALOUSLY STEEP REDDENING LAW IN QUASARS: AN EXCEPTIONAL EXAMPLE OBSERVED IN IRAS 14026+4341

A fraction of the heavily reddened quasars require a reddening curve which is even steeper than that of the Small Magellanic Cloud. In this paper, we thoroughly characterize the anomalously steep reddening law in quasars, via an exceptional example observed in IRAS 14026+4341. By comparing the observed spectrum to the quasar composite spectrum, we derive a reddening curve in the rest-frame wavelength range of 1200 {\AA}--10000 {\AA}. It is featured with a steep rise at wavelengths shorter than 3000 {\AA}, but no significant reddening at longer wavelengths. The absence of dust reddening in optical continuum is confirmed by the normal broad-line Balmer decrement (the H$\alpha$/H$\beta$ ratio) in IRAS 14026+4341. The anomalous reddening curve can be satisfactorily reproduced by a dust model containing silicate grains in a power-law size distribution, $dn(a)/da \propto a^{-1.4}$, truncated at a maximum size $a_{max}=70 {\rm nm}$. The unusual size distribution may be caused by the destruction of large "stardust" grains by quasar activities or a different dust formation mechanism (i.e., the in situ formation of dust grains in quasar outflows). It is also possible that the analogies of the dust grains observed toward the Galactic center is responsible for the steep reddening curve. In addition, we find that IRAS 14026+4341 is a weak emission-line quasar (i.e., PHL 1811 analogies) with heavy dust reddening and blueshifted broad absorption lines.

Microstructural characterization of mixed-material deposition layer on the LHD divertor tiles by using nano-geological diagnosis

Abstract Fusion plasma research crucially needs to understand the characteristics of the deposition layer that forms in the vacuum vessel because of the migration of plasma-facing materials. Such a deposition layer can accumulate on the fuel particles on account of a co-deposition process and can be a source of dust in the plasma. In this study, nano-geological diagnosis which uses a focused ion beam (FIB) fabrication technique and transmission electron microscope (TEM) observations, has been applied to the mixed-material deposition layer formed in a large helical device (LHD). A cross-sectional view of the deposition layer with nanometer resolution was successfully observed. The total thickness of the layer was estimated at ∼8 μm, and it has very fine and stratified layer structures in the nanometer level. The characteristics of each layer are indicative of the operational history of the LHD and the mechanism of dust formation by layer flaking.

Formation of Cr-Bearing Species in Stainless Steelmaking Dust by Induction Furnace

Stainless steelmaking dust contains significant levels of Cr-bearing phases (typically 0.28~16.5%). In this study, stainless steel was produced in an induction furnace, dust generated during the smelting process is collected in order to classify dust formation mechanisms and effects of operation parameters of smelting process on the formation of Cr(VI) species in the dust. The results showed that approximately 60% of dust generated during stainless steelmaking process by induction furnace is due to entrainment of charge fines, about 30% of dust formed due to metal and slag splashing result in oxygen and argon injection, and only about 10% of dust are formed through vaporization from the melt bath. In addition, the Cr-bearing phases in the dust mainly generate due to slag and metal splash. It can increase Cr(VI) content in the dust by increasing the chromium content in the molten steel, the amount of slag former and temperature of molten. To accelerate the cooling rate during the sampling period will decrease the Cr(VI) content in the dust.

Dust particle formation due to interaction between graphite and helicon deuterium plasmas

The collection of dust particles using divertor simulation helicon plasmas has been carried out to examine dust formation due to the interaction between a graphite target and deuterium plasmas, which are planned to operate in the large helical device (LHD) at the Japanese National Institute for Fusion Science (NIFS). The collected dust particles are classified into three types: (i) small spherical particles below 400nm in size, (ii) agglomerates whose primary particles have a size of about 10nm, and (iii) large flakes above 1μm in size. These features are quite similar to those obtained through hydrogen plasma operation, indicating that the dust formation mechanisms due to the interaction between a carbon wall and a plasma of deuterium, which is the isotope of hydrogen, is probably similar to those of hydrogen.

The Keck Aperture Masking Experiment: dust-enshrouded red giants

While the importance of dusty asymptotic giant branch (AGB) stars to galactic chemical enrichment is widely recognised, a sophisticated understanding of the dust formation and wind-driving mechanisms has proven elusive due in part to the difficulty in spatially-resolving the dust formation regions themselves. We have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture Masking Experiment, resolving all of them in multiple near-infrared bands between 1.5 microns and 3.1 microns. We find 45% of the targets to show measurable elongations that, when correcting for the greater distances of the targets, would correspond to significantly asymmetric dust shells on par with the well-known cases of IRC+10216 or CIT6. Using radiative transfer models, we find the sublimation temperature of 1130 +- 90 K and 1170 +- 60 K for silicates and amorphous carbon respectively, both somewhat lower than expected from laboratory measurements and vastly below temperatures inferred from the inner edge of YSO disks. The fact that O-rich and C-rich dust types showed the same sublimation temperature was surprising as well. For the most optically-thick shells (tau > 2 at 2.2 microns), the temperature profile of the inner dust shell is observed to change substantially, an effect we suggest could arise when individual dust clumps become optically-thick at the highest mass-loss rates.

Properties of steelmaking dust and the mechanism of its formation

Results are presented from studies of the properties of steelmaking dust and the main mechanisms of dust formation during steel production in basic oxygen converters and electric-arc furnaces. It is noted that the issue of the mechanism by which the dust is formed has not yet been definitively resolved. The dustgeneration process is intimately related to the process of decarbonization of the metal. As a working hypothesis, it can be argued that the main factor which determines the rate of dust formation and the rate of decarbonization of the metal is the maximum rate of flow of oxygen to a unit surface of the bath within the reaction zone. Experience shows that this factor can be used to optimize the process of oxygen blowing in different types of furnaces.

DUST PROPERTIES IN THE AFTERGLOW OF GRB 071025 AT z ∼ 5

At high redshift, the universe was so young that core-collapse supernovae (SNe) are suspected to be the dominant source of dust production. However, some observations indicate that the dust production by SNe is an inefficient process, casting doubts on the existence of abundant SNe-dust in the early universe. Recently, Perley et al. (2010) reported that the afterglow of GRB 071025 - an unusually red GRB at z ~ 5 - shows evidence for the SNe-produced dust. Since this is perhaps the only high redshift GRB exhibiting compelling evidence for SNe-dust but the result could easily be affected by small systematics in photometry, we re-examined the extinction properties of GRB 071025 using our own optical/near-infrared data at a different epoch. In addition, we tested SNe-dust models with different progenitor masses and dust destruction efficiencies to constrain the dust formation mechanisms. By searching for the best-fit model of the afterglow spectral energy distribution, we confirm the previous claim that the dust in GRB 071025 is most likely to originate from SNe. We also find that the SNe-dust model of 13 or 25M_{\odot} without dust destruction fits the extinction property of GRB 071025 best, while pair-instability SNe (PISNe) models with a 170M_{\odot} progenitor poorly fit the data. Our results indicate that, at least in some systems at high redshift, SNe with intermediate masses within 10 - 30M_{\odot} were the main contributors for the dust enrichment, and the dust destruction effect due to reverse shock was negligible.

Two Centuries of Observing R Coronæ Borealis

AbstractR Coronæ Borealis was found to be variable in the year 1783, and was one of the first variable stars to be so identified. Its class, the R Coronæ Borealis (RCB) stars, are rare hydrogen-deficient carbon-rich supergiants. RCB stars undergo massive declines of up to 8 mag due to the formation of carbon dust at irregular intervals. The mechanism of dust formation around RCB stars is not well understood, but the dust is thought to form in or near the atmosphere of the star. Their rarity may stem from the fact that they are in an extremely rapid phase of the evolution, or are in an evolutionary phase that most stars do not undergo. Several evolutionary models have been suggested to account for the RCB stars, including a merger of two white dwarfs (WDs) or a final helium-shell flash (FF) in a PN central star. The large overabundance of 18O found in most of the RCB stars favours the WD merger model, while the presence of Li in the atmospheres of five RCB stars favours the FF one. In particular, the measured isotopic abundances imply that many, if not most, RCB stars are produced by WD mergers, which may be the low-mass counterparts of the more massive mergers thought to produce type Ia supernovæ. Understanding these enigmatic stars depends to a large extent on continuous monitoring to catch their irregular but rapid variations caused by dust formation, their variations due to stellar pulsations, and long-term changes that may occur over centuries. I will use observations of R Coronæ Borealis obtained over 200 years to demonstrate what kinds of monitoring are necessary for these and similar classes of variables.

Dust in brown dwarfs and extra-solar planets

Context. This work is concerned with dust formation in ultra-cool atmospheres, encompassing the latest type stars, brown dwarfs, and hot giant exoplanets. Dust represents one of the most important and yet least understood sources of opacity in these types of objects.Aims. We compare our model spectra with SpeX data in order to draw conclusions about the dust cloud structure and related quantities in ultra-cool atmospheres. Methods. We use the self-consistent Drift-Phoenix atmosphere code, which features a kinetic dust formation mechanism and accounts for the dust cloud influence on the spectra. Results. We present fits of our latest model spectra to observations that cover a wide range of our model grid. The results are remarkably good, yielding significant improvement over the older Cond-/Dusty-Phoenix models, especially in the L-dwarf regime. The new models are able to properly reproduce observed spectra, including complicated features such as the molecular band strengths. This raises confidence in the reliability of our dust-modeling approach.Conclusions. We demonstrate that our code produces excellent results concerning the fitting with observations. This suggests that our dust cloud and atmosphere structures are reasonably accurate. Like all other current cloud models, ours is not able to produce satisfying results for spectral types later than L6 without manually tuning down the amount of dust. Our results show the formation of convective cells within the cloud, which are able to destroy the lower cloud parts. The dust opacity is reduced significantly without the need to tune the dust cloud thickness. There are indications that the cycle of dust accumulation and cloud destruction by convection is time-dependent on rather long timescales. Considering a statistical distribution of locally variable dust clouds over a dwarf’s surface can result in a large number of spectral configurations for the same model atmosphere parameters, hence introducing an additional and more or less random degree of freedom to those atmospheres. Without resorting to the model atmosphere parameters, this alone can account for the unusually red and blue objects that have been discovered.