Chromatic Effects Research Articles

Physicochemical Characterization of Cullet to Glaze for Environmental Sustainability and Entrepreneurial Development

Purpose: Inability of ceramists to formulate glazes locally and the cost of importing glazes had resulted to the closure of many cottage ceramic industries in Nigeria. The study, physicochemical characterization of cullet to glaze, was conducted with the aim of recycling cullet for glazing earthen wares and the intention was to conduct elemental analysis of waste glass for glaze recipes, determine its artistic usage, lessen cullet from environment and harness the chemical properties for industrial development and economic growth.
 Methodology: Methodologies for the study involved laboratory analysis to determine oxides concentration in the cullet and studio artistic techniques to form glaze batches, batch-milling, glazes application on earthenware, and kiln firing. Four colours of windowpane cullet were used in order to determine their chromaticity effects as glaze. Cullet were pulverised with pulveriser machine (Rocklabs) and elemental analysis was carried out with tandem accelerator machine, using Particle Induce X-ray Emission to determine oxide compositions and concentrations.
 Findings: Elemental analysis revealed Na2O, MgO, K2O, Al2O3, SiO2, CaO, TiO2, PbO and FeO. SO3, P3O5, ZrO2, Rb2O, ZnO, MoO3, Sb2O5, SrO and BaO in varying concentrations as the oxides in the samples. The glass ceramic glazes gave good matt, glossy, opalescent, translucent and opaque results at 950oC kiln temperature. The reactions of additive fluxes on each formulated glaze batch with windowpane cullet assist hydrokinetics nature of their crystallisation phases in the kiln.
 Unique Contributions to Theory, Practice and Policy: The study is hinged on the circular economy theory; an approach towards designing out of waste and regenerating natural system. It explicates artists’ ideas in recycling cullet for glaze derivation and highlights recycling benefits of cullet for environmental sustainability and entrepreneurial development. The study enhances the understanding of ceramists on how cullet can be utilized for glaze production and contributes to the development of practical strategies and solutions for stakeholders in ceramic field. The adaptation will ameliorate the problem of unavailability and high cost of glazes; stimulate rapid development of the Nigerian ceramic industry and heighten economic growth of Nigeria.

Computational refocusing in phase-unstable polarization-sensitive optical coherence tomography.

We present computational refocusing in polarization-sensitive optical coherence tomography (PS-OCT) to improve spatial resolution in the calculated polarimetric parameters and extend the depth-of-field in phase-unstable, fiber-based PS-OCT systems. To achieve this, we successfully adapted short A-line range phase-stability adaptive optics (SHARP), a computational aberration correction technique compatible with phase-unstable systems, into a Stokes-based PS-OCT system with inter-A-line polarization modulation. Together with the spectral binning technique to mitigate system-induced chromatic polarization effects, we show that computational refocusing improves image quality in tissue polarimetry of swine eye anterior segment ex vivo with PS-OCT. The benefits, drawbacks, and potential applications of computational refocusing in anterior segment imaging are discussed.

Оптическая система для малогабаритного космического аппарата дистанционного зондирования Земли формата CubeSat

The paper considers relevance of creating the small-sized high-resolution optical systems for the small spacecraft. It describes the current state of domestic and foreign systems engaged in the Earth remote sensing of the CubeSat format that confirmed the need to develop domestic multi-component satellite constellations. Unlike the large-sized spacecraft, the CubeSat standard implies introduction of the micro-format satellites. In order to reduce overall dimensions of the system and minimize the chromatic aberrations effect on the image quality in selecting the optical scheme components, mirrors are preferred, as a rule. Among all possible design schemes, the Ritchey --- Chretien optical scheme is the most promising due to its simplicity, small overall dimensions and high optical performance in a wide spectral range for the CubeSat satellites. Main optical and technical parameters, as well as the optical system characteristics for a small spacecraft are provided. For typical systems, the paper proposes a calculation technique; and a simulation model was created making it possible to assess the optical system image quality. The root-mean-square value of the point scatter spot radius in the image plane was taken as the criterion in evaluating the image quality. It is shown that the Ritchey --- Chretien optical scheme and its elements are characterized by its relative easiness in implementation due to using the studied technologies of the lens and mirror elements manufacture and ensuring high image quality and required overall dimensions, which makes it possible to use them in creating a multi-component satellite constellation

Shadows of rotating black holes in plasma environments with aberration effects

The shadows of black holes encode significant information about the properties of black holes and the spacetime surrounding them. So far, the effects of dispersive media, such as plasma, and relativistic aberration on the propagation of light around compact objects have been treated separately in the literature. In this paper, we will employ the Konoplya, Stuchl\'{\i}k, and Zhidenko family of stationary, axially symmetric, and asymptotically flat metrics to describe the spacetime around rotating black holes. We will study how the parameters of the black hole, the chromatic effects resulting from the presence of a nonmagnetized, pressureless plasma environment, and the effects of relativistic aberration of a moving observer modify the morphology of the shadow.

Phytochemical Synthesis of Silver Nanoparticles and Their Antimicrobial Investigation on Cotton and Wool Textiles.

The use of bio-based reagents for silver nanoparticle (AgNP) production has gained much attention among researchers as it has paved the way for environmentally friendly approaches at low cost for synthesizing nanomaterials while maintaining their properties. In this study, Stellaria media aqueous extract was used for silver nanoparticle phyto-synthesis, and the resulting treatment was applied to textile fabrics to test its antimicrobial properties against bacteria and fungi strains. The chromatic effect was also established by determining the L*a*b* parameters. For optimizing the synthesis, different ratios of extract to silver precursor were tested using UV-Vis spectroscopy to observe the SPR-specific band. Moreover, the AgNP dispersions were tested for their antioxidant properties using chemiluminescence and TEAC methods, and the phenolic content was evaluated by the Folin-Ciocâlteu method. For the optimal ratio, values of average size, 50.11 ± 3.25 nm, zeta potential, -27.10 ± 2.16 mV, and polydispersity index, 0.209, were obtained via the DLS technique and zeta potential measurements. AgNPs were further characterized by EDX and XRD techniques to confirm their formation and by microscopic techniques to evaluate their morphology. TEM measurements revealed cvasi-spherical particles with sizes in the range of 10-30 nm, while SEM images confirmed their uniform distribution on the textile fiber surface.

Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution

AbstractBACKGROUNDSodium chlorate (NaClO3) is extensively used in the paper industry, but its production uses strictly regulated highly toxic Na2Cr2O7 to reach high hydrogen evolution reaction (HER) Faradaic efficiencies. It is therefore important to find alternatives either to replace Na2Cr2O7 or reduce its concentration.RESULTSThe Na2Cr2O7 concentration can be significantly reduced by using Na2MoO4 as an electrolyte co‐additive. Na2MoO4 in the millimolar range shifts the platinum cathode potential to less negative values due to an activating effect of cathodically deposited Mo species. It also acts as a stabilizer of the electrodeposited chromium hydroxide but has a minor effect on the HER Faradaic efficiency. X‐ray photoelectron spectroscopy (XPS) results show cathodic deposition of molybdenum of different oxidation states, depending on deposition conditions. Once Na2Cr2O7 was present, molybdenum was not detected by XPS, as it is likely that only trace levels were deposited. Using electrochemical measurements and mass spectrometry we quantitatively monitored H2 and O2 production rates. The results indicate that 3 μmol L−1 Na2Cr2O7 (contrary to current industrial 10–30 mmol L−1) is sufficient to enhance the HER Faradaic efficiency on platinum by 15%, and by co‐adding 10 mmol L−1 Na2MoO4 the cathode is activated while avoiding detrimental O2 generation from chemical and electrochemical reactions. Higher concentrations of Na2MoO4 led to increased oxygen production.CONCLUSIONCareful tuning of the molybdate concentration can enhance performance of the chlorate process using chromate in the micromolar range. These insights could be also exploited in the efficient hydrogen generation by photocatalytic water splitting and in the remediation of industrial wastewater. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Spectroscopic and Imaging Analyses on Easel Paintings by Giovanni Santi

The most important painter from Urbino in the last decades of the 15th century (1439 ab.–1494) was Giovanni Santi, the father of Raphael. The lack of scientific literature about Santi’s practice and the possible peculiar role of Urbino in the development of painting techniques in northern Italy suggested in-depth investigations of the entire corpus of his paintings. A well-established sequence of multispectral imaging, spectroscopic and microscopic investigations was performed on 24 wood panel paintings and 2 canvases attributed by most scholars to Giovanni Santi (1439 ab.–1494) to collect a large set of significant data. This systematic research allowed his painting technique to be defined, starting from the type of supports he used and from the features of the underdrawing, which quite frequently included characteristic regular hatching. The pigments used were widely investigated by means of ED-XRF and reflectance spectroscopy (vis-RS); a meaningful multivariate statistical method (PCA and HCA analysis) was also applied to the ED-XRF dataset acquired for representative hues. In particular, the vis-RS technique proved to be a simple and effective diagnostic tool to detect many pigments, including indigo, and to distinguish between two different types of red lakes, avoiding sampling and more complex analyses. Santi used lead white, Fe-Mn-based pigments, vermilion, red lake, natural blue ultramarine, azurite, copper-based green pigments (particularly verdigris), lead-tin yellow, scarcely ever orpiment and, in a few green mixtures, also indigo. Despite the palette being linked to tradition, the master appeared to introduce some peculiarities, such as the addition of glass powder, and mixing pigments both in a traditional way and using them to create chromatic effects unusual for his time. This research confirmed that the systematic use of the integrated non-invasive methods is highly representative, and the results of this wide diagnostic campaign provided a significant dataset which allowed the implementation of a scientific database related to central Italy Renaissance paintings and materials.

Spectral Effects and Range of Focus in a Multizonal-Refractive Intraocular Lens Compared with a Standard Trifocal Diffractive Design.

This study was performed to compare the optical performance of a multizonal presbyopia-correcting intraocular lens (IOL) and a conventional trifocal model. The optical quality and simulated visual acuity (VA) of 570 Precizon Presbyopic NVA (OPHTEC BV) and AcrySof IQ PanOptix (Alcon) were compared. The Precizon features a refractive design consisting of alternating optical zones that converge the incident light into two principal foci and a transitional zone for intermediate vision. By contrast, the PanOptix applies a diffractive (non-apodized) profile to achieve trifocality. Simulated VA was derived from the modulation transfer function. Chromatic aberration effects were also studied. The diffractive and multizonal-refractive lenses yielded comparable simulated VAs at far focus (0.00 logMAR). All curves showed a reduction in expected VA with an increase in negative defocus. At -1.0 D, the multizonal-refractive IOL's VA dropped by 0.05 logMAR, but for the diffractive model, it was one line (0.11 logMAR). The multizonal-refractive lens's VA prediction at the secondary peak was 0.03 logMAR-minimally better than the 0.06 logMAR of the diffractive lens at -2.5 D. The refractive lens exhibited a 24% decrease in polychromatic optical quality due to material dispersion. The performance of PanOptix was more substantially affected, showing a 44% loss at 50 lp/mm at far, with minimal effects at other distances. The multizonal-refractive lens does not fall short of the established trifocal IOL, and it can be used to extend the visual range of pseudophakic patients. Although the multizonal-refractive lens has lower material dispersion, the diffractive model corrects chromatism beyond far focus.

“The Stuff That Dreams Are Made of”—Restoring Cinema Colors: A Roadmap for Real Research

Since 1895, through the analog and the digital eras, color is among the many narrative and aesthetic tools cinema language used in its creative process to shape a unique, multi-sensorial experience for its audience. Over these 120+ years, endless cinema color techniques, technologies, aesthetics, and ideologies came and went. One thing that stayed the same is that color in cinema, more than a technology, is a complex system made up by many components: filmmakers’ ideas and intent, negotiations with the audience, technologies (such as film stocks, chemicals, cameras, printers, developing machines, projectors), and laboratory processes and practices. Taken individually, none of these elements tells the whole story of color use and experience in cinematographic works. This complexity adds to the fact that much of film color technology history is not recorded in books, journals and patents and is often forgotten as so much of it relies on individuals’ practices and memories. Consequently, a novel and more comprehensive theoretical and methodological approach is needed in order to make it possible to preserve and restore cinema colors, that is, to faithfully recreate their original chromatic effects in a modern, completely different environment.

Analytical expressions for pulse profile of neutron stars in plasma environments

We present an analytical study of light curves of slowly rotating radio pulsars with emphasis on the chromatic effects derived from the presence of a plasma environment; analyzing the effects of the compactness, the metric model, and the electronic plasma density profile. After doing a numerical integration of the trajectories and luminosity curves of pulsars for different spherically symmetric metrics representing the exterior region of the pulsar, we generalize the approximate Beloborodov formula in order to include plasma corrections, obtaining simple analytical expressions for the trajectories and the observed flux and significantly simplifying the calculation of the pulse profiles by a drastic reduction of their computational cost. We study the errors committed by our approximation, comparing the numerical and analytical procedures. We also show how to use the new formalism to model the flux coming from different emission caps, not necessarily circular or antipodal and including the case of ring-shaped hot spots. Finally, we extend the classification introduced by Beloborodov to the case of two distinguishable, non-antipodal, finite size emission caps, showing the respective classification maps and some of the characteristic pulse profiles.

Potential scientific synergies in weak lensing studies between the CSST andEuclidspace probes

Aims.With the next generation of large surveys poised to join the ranks of observational cosmology in the near future, it is important to explore their potential synergies and to maximize their scientific outcomes. In this study, we aim to investigate the complementarity of two upcoming space missions:Euclidand the China Space Station Telescope (CSST), both of which will be focused on weak gravitational lensing for cosmology. In particular, we analyze the photometric redshift (photo-z) measurements by combining NUV,u, g, r, i, z, ybands from CSST with the VIS,Y, J, Hbands fromEuclid, and other optical bands from the ground-basedVera C. RubinObservatory Legacy Survey of Space and Time (LSST) and Dark Energy Survey. We also consider the advantages of combining the two space observational data in simplifying image deblending. ForEuclid, weak lensing measurements use the broad optical wavelength range of 550−900 nm, for which chromatic point-spread function (PSF) effects are significant. For this purpose, the CSST narrow-band data in the optical can provide valuable information forEuclidto obtain more accurate PSF measurements and to calibrate the color and color-gradient biases for galaxy shear measurements.Methods.We created image simulations, using theHubbleDeep UV data as the input catalog, for different surveys and quantified the photo-zperformance using theEAZYtemplate fitting code. For the blending analyses, we employed high-resolution HST-ACS CANDELSF606WandF814Wdata to synthesize mock simulated data forEuclid, CSST, and an LSST-like survey. We analyzed the blending fraction for different cases as well as the blending effects on galaxy photometric measurements. Furthermore, we demonstrated that CSST can provide a large enough number of high signal-to-noise ratio multi-band galaxy images to calibrate the color-gradient biases forEuclid.Results.The sky coverage ofEuclidlies entirely within the CSST footprint. The combination ofEuclidwith the CSST data can thus be done more uniformly than with the various ground-based data that are part of theEuclidsurvey. Our studies show that by combiningEuclidand CSST, we can reach a photo-zprecision ofσNMAD ≈ 0.04 and an outlier fraction ofη ≈ 2.4% at the nominal depth of theEuclidWide Survey (VIS < 24.5 AB mag). For CSST, including theEuclidY, J, Hbands reduces the overall photo-zoutlier fraction from ∼8.5% to 2.4%. Forz > 1, the improvements are even more significant. Because of the similarly high resolutions, the data combination ofEuclidand CSST can be relatively straightforward for photometry measurements. On the other hand, to include ground-based data, sophisticated deblending utilizing priors from high-resolution space observations are required. The multi-band data from CSST are very helpful in controlling the chromatic PSF effect forEuclidVIS shear measurements. The color-gradient bias forEuclidgalaxies with different bulge-to-total flux ratio at different redshifts can be well calibrated to the level of 0.1% using galaxies from the CSST deep survey.

Optical Field Recovery in Jones Space

Optical full-field recovery allows for fiber impairments compensation such as chromatic dispersion and polarization mode dispersion (PMD) in the digital signal processing. For cost-sensitive short-reach optical networks, some advanced single-polarization (SP) optical field recovery schemes are recently proposed to avoid chromatic dispersion-induced power fading effect and improve the spectral efficiency for larger potential capacity. Polarization division multiplexing (PDM) can further double both the spectral efficiency and the system capacity of these SP carrier-assisted direct detection (DD) schemes. However, the so-called polarization fading phenomenon induced by random polarization rotation is a fundamental obstacle that prevents SP carrier-assisted DD systems from polarization diversity. In this paper, we propose a receiver of Jones-space field recovery (JSFR) to realize polarization diversity with SP carrier-assisted DD schemes. Different receiver structures and simplified recovery procedures for JSFR are explored theoretically. The proposed JSFR pushes SP DD schemes towards PDM without an extra optical signal-to-noise ratio (OSNR) penalty. In addition, the JSFR shows good tolerance to PMD since the optical field recovery is conducted before polarization recovery. In the concept-of-proof experiment, we demonstrate 448-Gb/s reception over 80-km single-mode fiber using the proposed JSFR based on 2 × 2 couplers. Furthermore, we qualitatively compare the optical field recovery in Jones space and Stokes space in terms of the modulation dimension and hardware complexity.

Chemical and Chromatic Effects of Commercial Wine Yeast Strains (Saccharomyces spp.) on ‘Dolgo’ Crabapple Rosé Cider

Chemical and Chromatic Effects of Commercial Wine Yeast Strains (Saccharomyces spp.) on ‘Dolgo’ Crabapple Rosé Cider

Underwater hyperspectral imaging bioinspired by chromatic blur vision

In the underwater environment, conventional hyperspectral imagers for imaging target scenes usually require stable carrying platforms for completing push sweep or complex optical components for beam splitting in long gaze imaging, which limits the system’s efficiency. In this paper, we put forward a novel underwater hyperspectral imaging (UHI) system inspired by the visual features of typical cephalopods. We designed a visual bionic lens which enlarged the chromatic blur effect to further ensure that the system obtained blur images with high discrimination of different bands. Then, chromatic blur datasets were collected underwater to complete network training for hyperspectral image reconstruction. Based on the trained model, our system only required three frames of chromatic blur images as input to effectively reconstruct spectral images of 30 bands in the working light range from 430 nm to 720 nm. The results showed that the proposed hyperspectral imaging system exhibited good spectral imaging potential. Moreover, compared with the traditional gaze imaging, when obtaining similar hyperspectral images, the data sampling rate in the proposed system was reduced by 90%, and the exposure time of required images was only about 2.1 ms, reduced by 99.98%, which can greatly expand its practical application range. This experimental study illustrates the potential of chromatic blur vision for UHI, which can provide rapid response in the recognition task of some underwater dynamic scenarios.

Asymmetric 160/80 Gb/s TWDM PON with supported transmission method utilizing FBG and DML

Abstract The primary objective of time wavelength-division multiplexing passive optical networks (TWDM-PONs) development at the moment is the cost-effective capacity acquisition. This work addresses this issue by demonstrating a full-system TWDM-PON was selected as a primary choice to NG-PON2 by Full-service access network (FASN) unanimously agreed and International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.989. An asymmetric TWDM NG-PON2 was demonstrated that provides 160 Gbps downstream and 80 Gbps upstream which is the target capacity by ITU-T G.989.1 based on OptiSystem-7 software. We propose to use fiber Bragg grating (FBG) and Er-doped fiber amplifier (EDFA) to reduced both of the chromatic dispersion effect and system attenuation until given permission to enhance the distance communication system. The proposed system’s performance is evaluated and compared with other works and ITU-T G.989.2 recommendations to demonstrate how the system can be enhanced in terms of capacity, link distance, bit error rate (BER), Q-factor and receiver sensitivity. According to the results, the optimum possible distance under communication requirements (6 for the Q-factor and 10−9 for the BER) is around 65 km for the system with dispersion compensation. With the help of the low-cost directly modulated laser (DML) for uplink, we successfully improve the power budget to 41.2 dB along 65 km of bidirectional fiber at a 1:512 splitting ratio.

Three-level hierarchical micro/nanostructures on biopolymers by injection moulding using low-cost polymeric inlays

The industrial interest in the patterning of polymeric surfaces at the micro/nanoscale to include new functionalities has considerably increased during the last years. Hierarchical organization of micro/nanometric surface textures yields enhanced functional properties such as hydrophobicity, hydrophilicity, antibacterial activity, and optical or chromatic effects to cite some. While high accuracy methods to pattern hierarchical surfaces at the nanoscale have been developed, only some of them have been applied for high volume manufacturing with limited success, mainly because they rely on the use of expensive machinery and moulds or complicated inserts. Therefore, a method using low cost recyclable tooling and process conditions applicable to high-volume manufacturing is currently missing. In this work, a scalable and low-cost method to replicate hierarchical micro/nanostructured surfaces on plastic films is presented, which can be latter used as inlays for injection moulded parts with standard processing conditions. This method is used to demonstrate the feasibility of replicating three level hierarchical micro/nano textured surfaces using recyclable bio-based polymers (of high relevancy in the current plastic pollution context) achieving replication ratios above 90%, comparing the replication results with those obtained in polypropylene. The presence of the micro/nanotextures substantially increases the contact angle of all the polymers tested, yielding values higher than 90° in all the cases. Also, various mechanical properties of the replicated parts for all the polymers injected are characterized one and thirty days after the samples were manufactured, showing fairly constant values. This highlights the validity of the replicated surfaces, regardless of the biopolymers special crystallization characteristics.

9.1: Invited Paper: Pupil Size Estimation Model Based on Revised Spatially Weighted Corneal Flux Density and Chromaticity Coordinates

As an important parameter in studies on vision and ophthalmology, pupil size directly controls the amount of the light entering the human eye. Pupilometers or eye tracking systems are used to measure the pupil size in some studies while a pupil size estimation model can be applied when actual measurement is not available, such as in cases of optical design, photobiological safety studies, etc. There are several existing pupil size estimation models, most of which reveal the relationship between pupil size and spatial distribution of luminance. However, the radial asymmetry of spatial luminance weighting function in horizontal and vertical directions and the effect of light chromaticity on the human eye were investigated. In this paper, experiments were conducted to reveal the asymmetry of the spatial weighting function in the horizontal and vertical directions and the effect of chromaticity on the pupil size. A unified pupil size estimation model is proposed based on spatially weighted corneal flux density and chromaticity coordinates.

Performance Analysis of a Linear Gaussian- and tanh-Apodized FBG and Dispersion Compensating Fiber Design for Chromatic Dispersion Compensation in Long-haul Optical Communication Networks

This paper investigates a novel compensation technique of dispersion effect mitigation using a combination of three- and four-stage-apodized fiber Bragg gratings (FBG) and dispersion compensating fiber (DCF) designs. Two designs using three-stage and four-stage FBG and DCF in combination have been proposed and compared for their performance in mitigating chromatic dispersion effects at 100 km SMF. The performance of each design has been evaluated using Q-factor results using linear Gaussian- and tanh-apodized fiber Bragg gratings. Each profile manifested different Q-factor results over a range of 5 dBm, 7.5 dBm, and 10 dBm of CW laser power over FBG grating lengths from 4 mm to 8 mm. The results obtained using the three-stage and four-stage FBG and DCF designs showed that an apodization profile using a tanh function can be used successfully with FBG lengths from 4 mm to 8 mm, regardless of the CW launched power. In contrast, the results using a Gaussian apodization profile for three- and four-stage FBG and DCF designs are applicable to FBG lengths from 5 mm to 8 mm. Designs using three-stage FBG and DCF generated higher Q-factor results than designs using only four-stage FBG and DCF, regardless of the launched power. The highest Q-factor of 18.58 was obtained for three-stage tanh-apodized FBG and DCF used in combination for an FBG length of 6 mm. The highest result obtained for a three-stage Gaussian-apodized FBG and DCF design was a Q factor of 17.13 using an FBG length of 8 mm. The proposed method was also compared to current similar works and can be successfully implemented in long-haul optical communication.

Bayesian data analysis for sky-averaged 21-cm experiments in the presence of ionospheric effects

ABSTRACT The ionosphere introduces chromatic distortions on low frequency radio waves, and thus poses a hurdle for 21-cm cosmology. In this paper, we introduce time-varying chromatic ionospheric effects on simulated antenna temperature data of a global 21-cm data analysis pipeline, and try to detect the injected global signal. We demonstrate that given turbulent ionospheric conditions, more than 5 per cent error in our knowledge of the ionospheric parameters could lead to comparatively low evidence and high root-mean-square error (RMSE), suggesting a false or null detection. When using a constant antenna beam for cases that include data at different times, the significance of the detection lowers as the number of time samples increases. It is also shown that for observations that include data at different times, readjusting beam configurations according to the time-varying ionospheric conditions should greatly improve the significance of a detection, yielding higher evidences and lower RMSE, and that it is a necessary procedure for a successful detection when the ionospheric conditions are not ideal.

Modeling the Optical to Ultraviolet Polarimetric Variability from Thomson Scattering in Colliding-wind Binaries

Massive-star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding-wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first time the well-known generalized treatment of Brown et al. for variable polarization from binaries with the semianalytic solution for the geometry and surface density CWI shock interface between the winds based on Cantó et al. Our calculations include some simplifications in the form of inverse-square law wind densities and the assumption of axisymmetry, but in so doing they arrive at several robust conclusions. One is that when the winds are nearly equal (e.g., O+O binaries) the polarization has a relatively mild decline with binary separation. Another is that despite Thomson scattering being a gray opacity, the continuum polarization can show chromatic effects at ultraviolet wavelengths but will be mostly constant at longer wavelengths. Finally, when one wind dominates the other, as, for example, in WR+OB binaries, the polarization is expected to be larger at wavelengths where the OB component is more luminous and generally smaller at wavelengths where the WR component is more luminous. This behavior arises because, from the perspective of the WR star, the distortion of the scattering envelope from spherical is a minor perturbation situated far from the WR star. By contrast, the polarization contribution from the OB star is dominated by the geometry of the CWI shock.