Search

About 20% of the white dwarfs possess a magnetic field that may be detected by the splitting and/or polarization of their spectral lines. As they cool, the effective temperatures of the white dwarfs become so low that no spectral lines can be seen in the visible wavelength range. If their atmospheres are not polluted by the debris of a planetary system, these cool white dwarfs have featureless optical spectra. Until quite recently, very little was known about the incidence of magnetic fields in these objects. However, when observed with polarimetric techniques, a significant number of featureless white dwarfs reveal strong magnetic fields in their optical continuum spectra. Measuring the occurrence rate and strength of magnetic fields in old white dwarfs may help us to understand how these fields are generated and evolve. We report the results of an ongoing survey of cool white dwarfs with the high-precision broad-band polarimeter DIPOL-UF, which is deployed at the Nordic Optical Telescope on La Palma, Spain. This survey has led to the firm discovery of 13 new cool magnetic white dwarfs in the solar neighborhood so far, including six new detections that we report in this paper. [ABSTRACT FROM AUTHOR]

Methods of reconstructing holographic images of objects made of the composite based on carbon fibermodified acrylonitrile-butadiene styrene and a thin electrically conductive film are presented. Holograms are obtained in the axial scheme when the collimating lens is placed on the source axis. Results of comparison of the calculated frequency response of the model transmission coefficient with measurements on an experimental setup are presented. [ABSTRACT FROM AUTHOR]

Aims. DH Cephei is a well-known massive O+O-type binary system on the northern sky, situated at the center of young open cluster NGC 7380. Our high-precision multi-band polarimetry clearly reveals that variations of linear polarization in this system are synchronous with the phase of the orbital period. We used the observed variations of Stokes parameters q and u to derive the orbital inclination i, orientation Ω, and the direction of rotation. Moreover, in order to obtain a rough estimation of the interstellar polarization in the vicinity of DH Cep, we observed polarization arising from the neighboring stars in the cluster. Methods. We used the Dipo1–2 polarimeter in combination with the remotely controlled 60 cm Tohoku T60 telescope to obtain linear polarization measurements of DH Cep in the B, V, and R passbands at the accuracy level of ~0.003%. To obtain an estimation of interstellar polarization of DH Cep, we observed more than a dozen field stars identified as members of NGC 7380 and in the close proximity to DH Cep. A Lomb-Scargle period search was applied to the acquired polarization data to reveal the dominating frequency in polarization variations. We used a standard analytical method based on a two-harmonics Fourier fit to derive the inclination, orientation, and the direction of rotation of the binary orbit. Results. The variations of Stokes parameters in all three B, V, and R passbands clearly suggest an unambiguous periodic signal at 1.055 d with an amplitude of variations of ~0.2%, which corresponds to half of the known orbital period of 2.11 d. This type of polarization variability is expected for a binary system with light-scattering material distributed symmetrically with respect to the orbital plane. In addition to the regular polarization variability, there is a nonperiodic component, which is strongest in the B passband. In the V passband, we obtained our most reliable values for the orbital inclination i = 46° + 11°/ − 46° and an orientation of the orbit on the sky of Ω = 105° ± 55°, with 1σ confidence intervals. Using our best estimate of i and the polametric amplitude in the V passband, we estimated that the mass loss from the system is ~3.4 × 10−7M⊙ yr−1. The direction of the binary system rotation on the plane of the sky is clockwise. Our polarimetric observations of neighboring stars of DH Cep in NGC 7380 reveal that the polarization of the cluster stars is most likley due to aligned interstellar dust in the foreground. [ABSTRACT FROM AUTHOR]

Aims. The fact that the O-type close binary star system AO Cassiopeiae exhibits variable phase-locked linear polarization has been known since the mid-1970s. In this work, we re-observe the polarization arising from this system more than 50 yr later to better estimate the interstellar polarization and to independently derive the orbital parameters, such as inclination, i, orientation, Ω, and the direction of the rotation for the inner orbit from the phase-folded polarization curves of the Stokes q and u parameters. Methods. The Dipol-2 polarimeter was used to obtain linear polarization measurements of AO Cassiopeiae in the B, V, and R passbands with the T60 remotely controlled telescope at an unprecedented accuracy level of ~0.003%. We have obtained the first proper quantification of the interstellar polarization in the direction heading towards AO Cas by observing the polarization of three neighboring field stars. We employed a Lomb-Scargle algorithm and detected a clear periodic signal for the orbital period of AO Cas. The standard analytical method based on a two-harmonics Fourier fit was used to obtain the inclination and orientation of the binary orbit. Results. Our polarimetric data exhibited an unambiguous periodic signal at 1.76 days, thus confirming the orbital period of the binary system of 3.52 days. Most of the observed polarization is of interstellar origin. The de-biased values of the orbital inclination are i = 63° + 2°/−3° and orientation of Ω = 29º(209º) ± 8°. The direction of the binary system rotation on the plane of the sky is clockwise. [ABSTRACT FROM AUTHOR]

Polstar is a proposed NASA MIDEX mission that carries a high resolution UV spectropolarimeter capable of measure all four Stokes parameters onboard a 60 cm telescope. The mission has been designed to pioneer the field of time-domain UV spectropolarimetry. Time domain UV spectropolarimetry offers the best resource to determine the geometry and physical conditions of protoplanetary disks from the stellar surface to <5 AU. We detail two key objectives that a dedicated time domain UV spectropolarimetry survey, such as that enabled by Polstar or a similar mission concept, could achieve: 1) Test the hypothesis that magneto-accretion operating in young planet-forming disks around lower-mass stars transitions to boundary layer accretion in planet-forming disks around higher mass stars; and 2) Discriminate whether transient events in the innermost regions of planet-forming disks of intermediate mass stars are caused by inner disk mis-alignments or from stellar or disk emissions. [ABSTRACT FROM AUTHOR]

Polarimetry provides an avenue for probing the geometry and physical mechanisms producing optical radiation in many astrophysical objects, including stellar binary systems. We present the results of multiwavelength (BVR) polarimetric studies of a sample of historical black hole X-ray binaries, observed during their outbursts or in the quiescent (or near-quiescent) state. We surveyed both long- and short-period systems, located at different Galactic latitudes. We performed careful analysis of the interstellar polarization in the direction on the sources to reliably estimate the intrinsic source polarization. Intrinsic polarization was found to be small (<0.2 per cent) in sources observed in bright soft states (MAXI J0637−430 and 4U 1957+115). It was found to be significant in the rising hard state of MAXI J1820+070 at the level of ∼0.5 per cent and negligible in the decaying hard state and during its failed outbursts, while Swift J1357.2−0933  showed its absence in the rising hard state. Three (XTE J1118+480 , V4641 Sgr , V404 Cyg) sources observed during quiescence show no evidence of significant intrinsic polarization, while MAXI J1820+070  is the only black hole X-ray binary which showed substantial (>5 per cent) intrinsic quiescent-state polarization with a blue spectrum. The absence of intrinsic polarization at the optical wavelengths puts constraints on the potential contribution of non-stellar (jet, hot flow, accretion disc) components to the total spectra of black hole X-ray binaries. [ABSTRACT FROM AUTHOR]

In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy, whereas the filled bands underneath contribute little to conduction. Here, we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics that resemble those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common to all graphene-based superlattices. [ABSTRACT FROM AUTHOR]

We studied the variability of the linear polarization and brightness of the γ-ray binary LS I +61° 303. High-precision BVR photopolarimetric observations were carried out with the Dipol-2 polarimeter on the 2.2 m remotely controlled UH88 telescope at Mauna Kea Observatory and the 60 cm Tohoku telescope at Haleakala bservatory (Hawaii) over 140 nights in 2016−2019. We also determined the degree and angle of the interstellar polarization toward LS I +61° 303 using two out of four nearby field stars that have Gaia's parallaxes. After subtracting the interstellar polarization, we determined the position angle of the intrinsic polarization θ ≃ 11°, which can either be associated with the projection of the Be star's decretion disk axis on the plane of sky, or can differ from it by 90°. Using the Lomb-Scargle method, we performed timing analyses and period searches of our polarimetric and photometric data. We found statistically significant periodic variability of the normalized Stokes parameters q and u in all passbands. The most significant period of variability, PPol = 13.244 ± 0.012 d, is equal to one half of the orbital period Porb = 26.496 d. The fits of the polarization variability curves with Fourier series show a dominant contribution from the second harmonic which is typical for binary systems with circular orbits and nearly symmetric distribution of light scattering material with respect to the orbital plane. The continuous change of polarization with the orbital phase implies co-planarity of the orbit of the compact object and the Be star's decretion disk. Using a model of Thomson scattering by a cloud that orbits the Be star, we obtained constraints on the orbital parameters, including a small eccentricity e < 0.2 and periastron phase of ϕp ≈ 0.6, which coincides with the peaks in the radio, X-ray, and TeV emission. These constraints are independent of the assumption about the orientation of the decretion disk plane on the sky. We also extensively discuss the apparent inconsistency with the previous measurements of the orbital parameters from radial velocities. By folding the photometry data acquired during a three-year time span with the orbital period, we found a linear phase shift of the moments of the brightness maximum, confirming the possible existence of superorbital variability. [ABSTRACT FROM AUTHOR]

An electrical conductor subjected to a magnetic field exhibits the Hall effect in the presence of current flow. Here, we report a qualitative deviation from the standard behavior in electron systems with high viscosity. We found that the viscous electron fluid in graphene responds to nonquantizing magnetic fields by producing an electric field opposite to that generated by the ordinary Hall effect. The viscous contribution is substantial and identified by studying local voltages that arise in the vicinity of current-injecting contacts. We analyzed the anomaly over a wide range of temperatures and carrier densities and extracted the Hall viscosity, a dissipationless transport coefficient that was long identified theoretically but remained elusive in experiments. [ABSTRACT FROM AUTHOR]

Aims. The optical emission of black hole transients increases by several magnitudes during the X-ray outbursts. Whether the extra light arises from the X-ray heated outer disc, from the inner hot accretion flow, or from the jet is currently debated. Optical polarisation measurements are able to distinguish the relative contributions of these components. Methods. We present the results of BVR polarisation measurements of the black hole X-ray binary MAXI J1820+070 during the period of March-April 2018. Results. We detect small, ∼0.7%, but statistically significant polarisation, part of which is of interstellar origin. Depending on the interstellar polarisation estimate, the intrinsic polarisation degree of the source is between ∼0.3% and 0.7%, and the polarisation position angle is between ∼10 ° −30°. We show that the polarisation increases after MJD 58222 (2018 April 14). The change is of the order of 0.1% and is most pronounced in the R band. The change of the source Stokes parameters occurs simultaneously with the drop of the observed V-band flux and a slow softening of the X-ray spectrum. The Stokes vectors of intrinsic polarisation before and after the drop are parallel, at least in the V and R filters. Conclusions. We suggest that the increased polarisation is due to the decreasing contribution of the non-polarized component, which we associate with the the hot flow or jet emission. The low polarisation can result from the tangled geometry of the magnetic field or from the Faraday rotation in the dense, ionised, and magnetised medium close to the black hole. The polarized optical emission is likely produced by the irradiated disc or by scattering of its radiation in the optically thin outflow. [ABSTRACT FROM AUTHOR]

A procedure to synthesize (μ-hydroxo)bis-pentaaquarhodium(III) nitrate tetrahydrate [Rh2(H2O)8(μ-OH)2](NO3)4·4H2O from potassium hexachlororhodiate(III) is elaborated. The compound is isolated into the solid phase and structurally characterized. The crystallographic data are as follows: a = 5.8763(2) Å, b = 9.4749(4) Å, c = 9.6249(3) Å, α = 79.905(1)°, β = 84.324(1)°, γ = 82.922(1)°, space group P-1, Z = 1, ρcalc = 2.240 g/cm3. The compound is soluble in water, ethanol, and acetone. Hydrolysis takes place in concentrated nitric acid with the formation of mononuclear aqua- and aquanitrate complexes. Thermal decomposition of the salt at a temperature above 580 °C leads to the formation of a single product-rhodium(III) oxide. [ABSTRACT FROM AUTHOR]

Aims. To study the binary geometry of the classic Algol-type triple system λ Tau, we have searched for polarization variations over the orbital cycle of the inner semi-detached binary, arising from light scattering in the circumstellar material formed from ongoing mass transfer. Phase-locked polarization curves provide an independent estimate for the inclination i, orientation Ω and the direction of the rotation for the inner orbit. Methods. Linear polarization measurements of λ Tau in the B, V and R passbands with the high-precision Dipol-2 polarimeter have been carried out. The data have been obtained on the 60 cm KVA (Observatory Roque de los Muchachos, La Palma, Spain) and Tohoku 60 cm (Haleakala, Hawaii, USA) remotely controlled telescopes over 69 observing nights. Analytic and numerical modelling codes are used to interpret the data. Results. Optical polarimetry revealed small intrinsic polarization in &955; Tau with ∼0.05% peak-to-peak variation over the orbital period of 3.95 d. The variability pattern is typical for binary systems showing strong second harmonic of the orbital period. We apply a standard analytical method and our own light scattering models to derive parameters of the inner binary orbit from the fit to the observed variability of the normalized Stokes parameters. From the analytical method, the average for three passband values of orbit inclination i = 76° + 1°=/-2° and orientation Ω = 15°(195°) ± 2° are obtained. Scattering models give similar inclination values i = 72-76° and orbit orientation ranging from Ω = 16°(196°) to Ω = 19°(199°), depending on the geometry of the scattering cloud. The rotation of the inner system, as seen on the plane of the sky, is clockwise. We have found that with the scattering model the best fit is obtained for the scattering cloud located between the primary and the secondary, near the inner Lagrangian point or along the Roche lobe surface of the secondary facing the primary. The inclination i, inferred from polarimetry, agrees with the previously made conclusion on the semi-detached nature of the inner binary, whose secondary component is filling its Roche lobe. The non-periodic scatter, which is also present in the polarization data, can be interpreted as being due to sporadic changes in the mass transfer rate. [ABSTRACT FROM AUTHOR]

Our simultaneous three-colour (BVR) polarimetric observations of the low-mass black hole X-ray binary V404 Cyg show a small but statistically significant change of polarization degree (Δp ∼ 1 per cent) between the outburst in 2015 June and the quiescence. The polarization of V404 Cyg in the quiescent state agrees within the errors with that of the visually close (1.4 arcsec) companion (pR = 7.3 ± 0.1 per cent), indicating that it is predominantly of interstellar origin. The polarization pattern of the surrounding field stars supports this conclusion. From the observed variable polarization during the outburst, we show that the polarization degree of the intrinsic component peaks in the V band, pV = 1.1 ± 0.1 per cent, at the polarization position angle of θV =-7° ± 2°, which is consistent in all three passbands. We detect significant variations in the position angle of the intrinsic polarization in the R band from -30° to ∼0° during the outburst peak. The observed wavelength dependence of the intrinsic polarization does not support non-thermal synchrotron emission from a jet as a plausible mechanism, but it is in better agreement with the combined effect of electron (Thomson) scattering and absorption in a flattened plasma envelope or outflow surrounding the illuminating source. Alternatively, the polarization signal can be produced by scattering of the disc radiation in a mildly relativistic polar outflow. The position angle of the intrinsic polarization, nearly parallel to the jet direction (i.e. perpendicular to the accretion disc plane), is in agreement with these interpretations. [ABSTRACT FROM AUTHOR]

In this study, we proposed photocatalysts based on graphite-like carbon nitride with a low content (0.01–0.5 wt.%) of noble metals (Pd, Rh) for hydrogen evolution under visible light irradiation. As precursors of rhodium and palladium, labile aqua and nitrato complexes [Rh2(H2O)8(μ-OH)2](NO3)4∙4H2O and (Et4N)2[Pd(NO3)4], respectively, were proposed. To obtain metallic particles, reduction was carried out in H2 at 400 °C. The synthesized photocatalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy and high-resolution transmission electron microscopy. The activity of the photocatalysts was tested in the hydrogen evolution from aqueous and aqueous alkaline solutions of TEOA under visible light with a wavelength of 428 nm. It was shown that the activity for the 0.01–0.5% Rh/g-C3N4 series is higher than in the case of the 0.01–0.5% Pd/g-C3N4 photocatalysts. The 0.5% Rh/g-C3N4 sample showed the highest activity per gram of catalyst, equal to 3.9 mmol gcat–1 h–1, whereas the most efficient use of the metal particles was found over the 0.1% Rh/g-C3N4 photocatalyst, with the activity of 2.4 mol per gram of Rh per hour. The data obtained are of interest and can serve for further research in the field of photocatalytic hydrogen evolution using noble metals as cocatalysts. [ABSTRACT FROM AUTHOR]

Aims. Interstellar polarization of starlight at high galactic latitudes gives informationon the direction of the local Galactic magnetic field and the distribution of cosmic dustin wide "windows" perpendicular to the Galactic plane. Polarization data allow us to construct for the first time high-latitude polarization maps with resolution and sky coveragehigh enough to examine in detail the distribution of the interstellar polarization and the direction of the Galactic magnetic field around Galactic poles. Methods. We measured the polarization for more than 2400 new stars at distances of up to 600 pc and within 60° and 30° from the north and south Galactic poles. Here we describe the measurements and properties of the resulting total sample of about 3600 stars (completeness, radial distribution), and present polarization maps of the regions around the north (b > 30°) and south (b > 60°) poles. Results. The new interstellar polarization maps give wider and higher resolution views around the Galactic poles than previous maps. The major patterns in the maps are significant asymmetries in the polarization, one in the northern sky directly across the local spiral and the second between the northern and southern Galactic hemispheres. We confirm thatthere is significantly more interstellar polarization at high southern latitudes than at high northern latitudes within the local spiral. A comparison of our optical polarization map with the proposed models using local dust- and gas shells, (i.e.,Weaver's Loop I superbubble,Wolleben's two-bubble model, the interaction between the Local Bubble and the Loop I superbubble) reveals interesting features. 1) The optical and radio polarizations arelower in the eastern than in the western branch of Loop I, which may be caused by a weaker effective magnetic field in the eastern part where the diffuse IRAS emission is bright;this illustrates that low optical polarization does not always imply little dust. 2) We can see a clear signature of the western side of Wolleben's S2 shell (at 35 < l < 55), while there is no alignment of the polarization directions along the suggested wall of S2 inthe eastern part, though the alignment along S1 is visible. 3) In the upper parts of the suggested interaction zone between the Local Bubble and the Loop I superbubble our data show polarizations aligned along the zone contour. The week and rather randomly directed polarizations measured previously in the eastern part of this region may reflect the shorter distances (<250 pc) in the investigated sample of stars. [ABSTRACT FROM AUTHOR]

Aims. The intensity profiles of the C2 Swan bands in cool DQ white dwarfs cannot be adequately fitted with models that otherwise succesfully reproduce spectral features of the molecule CH in these stars. Initial modelling showed that a two-component atmosphere in the style of a spot might be able to solve the problem. Methods. We photometrically observed the two cool DQ white dwarfs GJ1117 and EGGR78 to search for variability caused by stellar spots. Results. We have not found any such variability, but we estimate the effects of hypothetical spots on lightcurves. We also estimate detection probabilities for spots in different configurations. Alternative explanations of the problem are needed and briefly discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrogarnet-type salt Ca 3 [Rh(OH) 6 ] 2 was used for Rh/TiO 2 preparation for first time. • Hydrogen evolution from ethanol solutions was successfully performed (λ = 380 nm) • In situ reduction of Ca 3 [Rh(OH) 6 ] 2 /TiO 2 to Rh/TiO 2 during H 2 evolution was observed. • The highest activity 3.3 mmol·h−1·g−1 with AQE = 1.8% was achieved for 0.1% Rh/TiO 2. • Unprecedent activity per gram of rhodium (21 mol·h−1) was registered for 0.01% Rh/TiO 2. A novel protocol for the preparation of Rh-decorated TiO 2 photocatalysts with the rhodium content of 0.01–1.0 wt% has been developed based on the deposition of the low-soluble hydrogarnet type salt Ca 3 [Rh(OH) 6 ] 2. Under 380-nm irradiation in water–ethanol mixtures the photoinduced reduction of Ca 3 [Rh(OH) 6 ] 2 /TiO 2 results in the formation of highly active Rh/TiO 2 photocatalysts with nanoparticulated rhodium co-catalyst preferably attached to the surface of anatase particles. The catalysts generate up to 21 mol of H 2 per gram of rhodium per hour via a photocatalytic hydrogen evolution reaction (HER) outperforming the activity of the analogous materials reported to date. [ABSTRACT FROM AUTHOR]

A unified analytical treatment of the Malmquist bias is presented. Depending on the data under consideration and on the way the mean values of absolute magnitude are calculated, three different types of Malmquist bias appear: integral bias, and magnitude- and distance-dependent ones. An analytical consideration of the distance-dependent bias, previously studied in extragalactic astronomy, is given in terms of the trigonometric parallax. In a quantitative treatment of the Spaenhauer diagram, in which the derived absolute magnitude is plotted versus the true parallax, we developed an easy-to-use method for determination of the region unaffected by the bias (‘unbiased plateau’). Considering spectroscopic distance indicators, we point out that for any magnitude-limited sample spectroscopic distance and parallax approach constant limits as the true distance increases. We draw some examples from luminosity calibrations of stellar classes. A brief outline is also given of a tentative course of investigations, anticipating future space astrometry missions. [ABSTRACT FROM AUTHOR]

The compound (1) is isolated by keeping sulfuric acid solutions of the [PtIV(H2O)2(OH)4] platinum hydroxide with an addition of 18-crown-6-ether. The structure of 1 (C2/c, a = 20.276(1) Å, b = 7.5844(5) Å, c = 13.8876(9) Å; β = 113.466(4)°; V = 1959.0(2) Å3; Z = 4) is determined by XRD and is shown to be formed by binuclear anionic platinum(III) aquasulfate complexes (containing bridging sulfate ligands and axial aqualigands), hydronium cations, and water molecules. The (2) compound, containing no solvate water molecules, is prepared from a solution of the (Bu4N)2[PtIV(NO3)6] salt in strong sulfuric acid. The structure of 2 (P21, a = 7.4384(7) Å, b = 13471(1) Å, c = 7.566(1) Å; β = 101.419(4)°; V = 743.1(1) Å3; Z = 2), containing no solvate water molecules, is determined by XRD. The substances are characterized by Raman and NMR spectroscopy methods. The geometry of the anion is additionally calculated by the DFT method; the optimized model agrees well with structural data and confirms a presence of Pt–Pt bonding. Possible mechanisms of the formation of platinum(III) complexes in sulfate solutions of platinum(IV) compounds are discussed. [ABSTRACT FROM AUTHOR]

Discovery of pulsations from a number of ultra-luminous X-ray (ULX) sources proved that accretion onto neutron stars can produce luminosities exceeding the Eddington limit by several orders of magnitude. The conditions necessary to achieve such high luminosities as well as the exact geometry of the accretion flow in the neutron star vicinity are, however, a matter of debate. The pulse phase-resolved polarization measurements that became possible with the launch of the Imaging X-ray Polarimetry Explorer (IXPE) can be used to determine the pulsar geometry and its orientation relative to the orbital plane. They provide an avenue to test different theoretical models of ULX pulsars. In this paper we present the results of three IXPE observations of the first Galactic ULX pulsar Swift J0243.6+6124 during its 2023 outburst. We find strong variations in the polarization characteristics with the pulsar phase. The average polarization degree increases from about 5% to 15% as the flux dropped by a factor of three in the course of the outburst. The polarization angle (PA) as a function of the pulsar phase shows two peaks in the first two observations, but changes to a characteristic sawtooth pattern in the remaining data set. This is not consistent with a simple rotating vector model. Assuming the existence of an additional constant polarized component, we were able to fit the three observations with a common rotating vector model and obtain constraints on the pulsar geometry. In particular, we find the pulsar angular momentum inclination with respect to the line of sight of ip = 15°–40°, the magnetic obliquity of θp = 60°–80°, and the pulsar spin position angle of χp ≈ −50°, which significantly differs from the constant component PA of about 10°. Combining these X-ray measurements with the optical PA, we find evidence for at least a 30° misalignment between the pulsar angular momentum and the binary orbital axis. [ABSTRACT FROM AUTHOR]

The cross section was measured at center of mass (c.m.) energies from the threshold to 1908 MeV. The experiment to measure the cross section has been carried out at the VEPP-2000 collider in 13 energy points. The SND detector is used to detect the produced neutron–antineutrons () events. A special time measurement system on the calorimeter was used to select the time-delayed events. The measured cross section is 0.4–0.6 nb. The neutron effective timelike form factor in the energy range under study varies from 0.3 to 0.6. [ABSTRACT FROM AUTHOR]

Abstract: We present the new results on the , , processes obtained by the SND. We also give a short report on VEPP-2000, the new collider constructed in Novosibirsk. The physical program for this machine is discussed. Special attention is paid to the future nucleon timelike form factor measurements. [Copyright &y& Elsevier]

• The method for deposition of rhodium(III) hydroxocomplexes with variable nuclearity onto the alumina support was developed. • The catalytic activity of prepared materials was evaluated in the benzaldoxime to benzamide rearrangement under eco-friendly conditions. • The higher catalytic activity of catalysts containing polynuclear hydroxocomplexes in comparison with mononuclear species was demonstrated. • Rhodium subnanoclusters formed in the reaction conditions were proposed as the active sites of the catalysts. • The superiority of polinuclear species was attributed to the pre-organized structure and higher dispersity. Rhodium(III) hydroxide was shown previously to possess the catalytic activity in the rearrangement reaction of primary oximes to amides. Alkaline solutions of rhodium(III) chlorocomplexes are routinely used for Rh(OH) 3 preparation and allow for a diversity of rhodium hydroxocomplexes that hold a wide range of catalytic properties. In this study, two Al 2 O 3 supported catalysts containing 1) exclusively [Rh(OH) 6 ]3− species and 2) a mixture of rhodium hydroxocomplexes with one to four rhodium atoms ([Rh(OH) 6 ]3–, [Rh 2 (μ−OH) 2 (OH) 8 ]4–, [Rh 3 (μ−OH) 3 (OH) 12 ]6–, [Rh 4 (μ−OH) 6 (OH) 12 ]6) were prepared, characterised (XRD, Raman, EXAFS) and tested in the benzaldoxime to benzamide rearrangement. The catalyst containing polynuclear complexes possessed at least three times higher turnover frequency (TOF) and better selectivity than the [Rh(OH) 6 ]3– based catalyst. According to the EXAFS data, the reduction of rhodium(III) took place under reaction conditions yielding small rhodium clusters (CN Rh-Rh = 4), which were proposed to be the active sites of catalysts. [ABSTRACT FROM AUTHOR]

The observational signatures of black holes in x-ray binary systems depend on their masses, spins, accretion rate, and the misalignment angle between the black hole spin and the orbital angular momentum. We present optical polarimetric observations of the black hole x-ray binary MAXI J1820+070, from which we constrain the position angle of the binary orbital. Combining this with previous determinations of the relativistic jet orientation, which traces the black hole spin, and the inclination of the orbit, we determine a lower limit of 40° on the spin-orbit misalignment angle. The misalignment must originate from either the binary evolution or black hole formation stages. If other x-ray binaries have similarly large misalignments, these would bias measurements of black hole masses and spins from x-ray observations. [ABSTRACT FROM AUTHOR]

We describe the first complete polarimetric data set of the entire outburst of a low-mass black hole X-ray binary system and discuss the constraints for geometry and radiative mechanisms it imposes. During the decaying hard state, when the optical flux is dominated by the non-thermal component, the observed polarization is consistent with the interstellar values in all filters. During the soft state, the intrinsic polarization of the source is small, ∼0.15 per cent in B and V filters, and is likely produced in the irradiated disc. A much higher polarization, reaching ∼0.5 per cent in V and R filters, at a position angle of ∼25○ observed in the rising hard state coincides in time with the detection of winds in the system. This angle coincides with the position angle of the jet. The detected optical polarization is best explained by scattering of the non-thermal (hot flow or jet base) radiation in an equatorial wind. [ABSTRACT FROM AUTHOR]

The expediency of capillary zone electrophoresis application in the study of a mixture of rhodium(III) hydroxocomplexes is shown for the species formed during the thermal treatment of [Rh(OH)6]3− at 60 °C in alkaline media. As these compounds are unstable in solution because of polycondensation at pH > 10 and the formation of insoluble rhodium(III) hydroxides at pH 5–10, their acidic derivatives with terminal aqua ligands acted as the objects of the study. Optimal separation conditions were achieved using sodium perchlorate as a background electrolyte, a voltage of +20 kV and pH 2.6. Rhodium(III) species with different nuclearities were identified in accordance with their UV spectra and the regularities of electrophoretic migration in the capillary. The presence of a dimer was also verified by the spiking of the mixture under investigation with a previously synthesised complex [Rh2(μ-OH)2(H2O)8](NO3)4, which confirms the correct identification. [ABSTRACT FROM AUTHOR]

Results are presented from measuring the cross section and effective neutron timelike form factor. Data are collected in 2020–2021 at the VEPP-2000 collider in the 1891 to 2007 MeV center-of-mass range of energies. The general purpose nonmagnetic SND detector is used to detect neutron–antineutron events. The time-of-flight approach is used to select events. The measured cross section is 0.4–0.6 nbn. The neutron form factor in the investigated range of energies varies from 0.3 to 0.2. [ABSTRACT FROM AUTHOR]

The cross section is measured in the center-of-mass energy range from 1.07 to 2.00 GeV in the decay channel , . The data set with an integrated luminosity of 242 pb accumulated in the experiment with the SND detector at the VEPP-2000 collider is analyzed. [ABSTRACT FROM AUTHOR]

The highly variable blazar OJ 287 is commonly discussed as an example of a binary black hole system. The 130 yr long optical light curve is well explained by a model where the central body is a massive black hole of 18.35 |$\times$| 109 solar mass that supports a thin accretion disc. The secondary black hole of 0.15 |$\times$| 109 solar mass impacts the disc twice during its 12 yr orbit, and causes observable flares. Recently, it has been argued that an accretion disc with a typical Active Galactic Nuclei (AGN) accretion rate and above mentioned central body mass should be at least six magnitudes brighter than OJ 287's host galaxy and would therefore be observationally excluded. Based on the observations of OJ 287's radio jet, detailed in Marscher and Jorstad (2011), and up-to-date accretion disc models of Azadi et al. (2022), we show that the V -band magnitude of the accretion disc is unlikely to exceed the host galaxy brightness by more than one magnitude, and could well be fainter than the host. This is because accretion power is necessary to launch the jet as well as to create electromagnetic radiation, distributed across many wavelengths, and not concentrated especially on the optical V -band. Further, we note that the claimed V -band concentration of accretion power leads to serious problems while interpreting observations of other AGN. Therefore, we infer that the mass of the primary black hole and its accretion rate do not need to be smaller than what is determined in the standard model for OJ 287. [ABSTRACT FROM AUTHOR]

The paper presents theoretical calculations and experimental data on the permittivity of conductive porous acrylonitrile butadiene styrene. It is found that spectrum regions with differential absorption are caused by the volume resonance of electromagnetic waves inside pores and in the matrix material between them. Resonant frequencies with increased differential absorption can be controlled by changing the pore space, dimension, and matrix permittivity. [ABSTRACT FROM AUTHOR]

The interstellar magnetic field (ISMF) near the heliosphere is a fundamental component of the solar galactic environment that can only be studied using polarized starlight. The results of an ongoing survey of the linear polarizations of local stars are analyzed with the goal of linking the ISMF that shapes the heliosphere to the nearby field in interstellar space. We present new results on the direction of the magnetic field within 40 pc obtained from analyzing polarization data using a merit function that determines the field direction that provides the best fit to the polarization data. Multiple magnetic components are identified, including a dominant interstellar field, , that is aligned with the direction ℓ, b = 36.°2, 49.°0 (±16.°0). Stars tracing have the same mean distance as stars that do not trace , but show weaker average polarizations consistent with a smaller column density of polarizing material. is aligned with the ISMF traced by the IBEX Ribbon to within degrees. The variations in the polarization position angle directions derived from the data that best match indicate a low level of magnetic turbulence, ∼9° ± 1°. The direction of is obtained after excluding polarization data tracing a separate magnetic structure that appears to be associated with interstellar dust deflected around the heliosphere. The velocities of local interstellar clouds relative to the Local Standard of Rest (LSR) increase with the angles between the LSR velocities and , indicating that the kinematics of local interstellar material is ordered by the ISMF. The Loop I superbubble that extends close to the Sun contains dust that reddens starlight and whose distance is determined by the color excess E(B − V) of starlight. Polarizations caused by grains aligned with respect to are consistent with the location of the Sun in the rim of the Loop I superbubble. An angle of between and the bulk LSR velocity the local interstellar material indicates a geometry that is consistent with an expanding superbubble. The efficiency of grain alignment in the local interstellar medium has been assessed using stars where both polarization data and hydrogen column density data are available. Nearby stars appear to have larger polarizations than expected based on reddened sightlines, which is consistent with previous results, but uncertainties are large. Optical polarization and color excess E(B − V) data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B − V) indicates an optical extinction of AV > 0.6 in the BICEP2 field, while the polarization data indicate that AV > 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region. [ABSTRACT FROM AUTHOR]

We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January–February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on the pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. We then show that the observed PA phase dependence in both observations can be explained with a single set of RVM parameters defining the pulsar's geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind. [ABSTRACT FROM AUTHOR]

The bright blazar OJ 287 routinely parades high brightness bremsstrahlung flares, which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a binary system. The accretion disc is not rigid but rather bends in a calculable way due to the tidal influence of the secondary. Next, we refer to this phenomenon as a variable disc level. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on general relativity inspired modified Kepler equation, which explains impact flares since 1888. The 2022 impact flare, namely flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12-yr cycle. This is the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ 287. It turns out that the arrival epoch of flare number 26 is sensitive to the level of primary SMBH's accretion disc relative to its mean level in our model. We incorporate these tidally induced changes in the level of the accretion disc to infer that the thermal flare should have occurred during 2022 July–August, when it was not possible to observe it from the Earth. Thereafter, we explore possible observational evidence for certain pre-flare activity by employing spectral and polarimetric data from our campaigns in 2004/05 and 2021/22. We point out theoretical and observational implications of two observed mini-flares during 2022 January–February. [ABSTRACT FROM AUTHOR]

The scanning superconducting quantum interference device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile tool for the nanoscale imaging of magnetic, thermal, and transport properties of microscopic devices of quantum materials. We present the design and performance of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight cell mounted at the bottom of the probe and is suspended by springs to suppress vibrations caused by the pulse tube cryocooler. Two capillaries allow for the in situ control of helium exchange gas pressure in the cell that is required for thermal imaging. A nanoscale heater is used to create local temperature gradients in the sample, which enables quantitative characterization of relative vibrations between the tip and the sample. The spectrum of the vibrations shows distinct resonant peaks with a maximal power density of about 27 nm/Hz1/2 in the in-plane direction. The performance of the SQUID-on-tip microscope is demonstrated by magnetic imaging of the MnBi2Te4 magnetic topological insulator, magnetization and current distribution imaging in a SrRuO3 ferromagnetic oxide thin film, and thermal imaging of dissipation in graphene. [ABSTRACT FROM AUTHOR]

We report the results from follow-up observations of two Roche-lobe filling hot subdwarf binaries with white dwarf companions predicted to have accretion discs. ZTF J213056.71+442046.5 (ZTF J2130) with a 39-min period and ZTF J205515.98+465106.5 (ZTF J2055) with a 56-min period were both discovered as subdwarf binaries with light curves that could only be explained well by including an accretion disc in their models. We performed a detailed high-resolution spectral analysis, using Keck/ESI to search for possible accretion features for both objects. We also employed polarimetric analysis using the Nordic Optical Telescope (NOT) for ZTF J2130. We did not find any signatures of an accretion disc in either object, and placed upper limits on the flux contribution and variation in degree of polarization due to the disc. Owing to the short 39-min period and availability of photometric data over 6 yr for ZTF J2130, we conducted an extensive O − C timing analysis in an attempt to look for orbital decay due to gravitational wave radiation. No such decay was detected conclusively, and a few more years of data paired with precise and consistent timing measurements were deemed necessary to constrain |$\dot{P}$| observationally. [ABSTRACT FROM AUTHOR]

A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging X-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray–emitting region. The polarization degree is 4.01 ± 0.20% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. These observations reveal that hot x-ray–emitting plasma is spatially extended in a plane perpendicular to, not parallel to, the jet axis. [ABSTRACT FROM AUTHOR]

The process e + e - → n n ¯ is studied in the experiment at the VEPP-2000 e + e - collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic calorimeter is used to select n n ¯ events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity. [ABSTRACT FROM AUTHOR]

Aims. Following our recent discovery of a new magnetic DQ white dwarf (WD) with CH molecular features, we report the results for the rest of the DQ WDs from our survey. Methods. We use high signal-to-noise spectropolarimetric data to search for magnetic fields in a sample of 11 objects. Results. One object in our sample, WD1235+422, shows the signs of continuum circular polarization that is similar to some peculiar DQs with unidentified molecular absorption bands, but the low signal-to-noise ratio and spectral resolution of these data make more observations necessary to reveal the true nature of this object. [ABSTRACT FROM AUTHOR]

The social behavior of Myotis daubentonii bats was studied in experimental groups kept in an openair cage. The repertoire of identification, aggressive, and friendly (integration) behaviors was described. Analysis of their frequencies showed that interactions between the animals were for the most part friendly (61.6%), while aggressive displays were rare (4.6%). Differences in behavior depending on sex and age were revealed: avoidance of contact and aggressive vocalization were observed significantly more frequently in young and adult males than in females. The bats in the experimental groups personally distinguished each other; in group 4, a two-level hierarchy was established (a dominant male vs. all other bats), which could be explained by specific conditions in the open-air cage. [ABSTRACT FROM AUTHOR]

In the energy range from 1.05 to 1.38 GeV, the upper limits for the cross sections of e e → f(600)γ, f(980)γ, f(1350)γ, and f(1270)γ → ππγ processes have been established. Measurements are performed in accordance with the statistics gathered in experiment with a spherical neutral detector (SND) on the VEPP-2M e e collider. The resultant upper limits vary from 6 to 42 pb depending on the energy and the model. [ABSTRACT FROM AUTHOR]

The e e → ηππ cross section in the η → 2γ channel has been measured in the $$ \sqrt s $$ = 1.04- to 1.38-GeV energy range. The data with a total integrated luminosity of 9.05 pb were collected on a spherical neutral detector at the VEPP-2M collider. The results are consistent with the BaBar and CMD2 data and have a higher statistical accuracy. [ABSTRACT FROM AUTHOR]

We have searched for the process e+e- → K+K-π0 at energies up to 1.38 GeVin an experiment with the spherical neutral detector at the VEPP-2M e+e- collider. The upper limits of the cross sections for the processes σ(e+e →; φπ: → K+K-π0) < 0.023 nb and σ(e+e- → KK*(892) → K+K-π0) < 0.059 nb have been established at a 95% confidence level. [ABSTRACT FROM AUTHOR]

The cross section for the process e+ e− → π+π−π0π0 has been measured in an experiment with a spherical neutral detector, with the cross section at energies √ s < 920 MeV having been measured for the first time. The model of vector dominance describes well the data obtained if the ρ, ρ′, and ρ″ resonances are taken into account. The probability of the decay ρ → π+π−π0π0 is B(ρ → π+π−π0π0) = (1.60 ± 0.74 ± 0.18) × 10−5. The upper limit for the decay ω → π+π−π0π0 has been improved by two orders of magnitude compared to previous measurements and is B(ω → π+π−π0π0) < 2 × 10−4 at a 90% confidence level. [ABSTRACT FROM AUTHOR]

The e + e − → ω, ρ → π0 e + e − processes have been investigated in the experiments with Spherical Neutral Detector at the VEPP-2M e + e − collider. The measurements provide the probability ℬ(ω → π0 e + e −) = (0.761 ± 0.053 ± 0.064) × 10−3 of the ω → π0 e + e g- conversion decay and the upper limit ℬ(ρ → π0 e + e −) < 1.2 × 10−5 (at 90% CL) for the ρ → π0 e + e − decay. The transition form factor was measured at three values of the 4-momentum transfer squared. [ABSTRACT FROM AUTHOR]

We present a measurement of the e + e − → K S K L cross section in the energy range √ s = 1.04−1.38 GeV. For an energy of √ s ≥ 1.2 GeV the cross section exceeds vector meson dominance model predictions with only ρ(770), ω(783), and ϕ(1020) mesons taken into account. The measured cross section agrees well with previous measurements. [ABSTRACT FROM AUTHOR]