Conditions in the WR 140 wind-collision region revealed by the 1.083-μm He i line profile.

We present spectroscopy of the P Cygni profile of the 1.083-μm He i line in the WC7 + O5 colliding-wind binary (CWB) WR 140 (HD 193793), observed in 2008, before its periastron passage in 2009, and in 2016–17, spanning the subsequent periastron passage. Both absorption and emission components showed strong variations. The variation of the absorption component as the O5 star was occulted by the wind-collision region (WCR) sets a tight constraint on its geometry. While the sightline to the O5 star traversed the WCR, the strength and breadth of the absorption component varied significantly on time-scales of days. An emission sub-peak was observed on all our profiles. The variation of its radial velocity with orbital phase was shown to be consistent with formation in the WCR as it swung round the stars in their orbit. Modelling the profile gave a measure of the extent of the sub-peak forming region. In the phase range 0.93–0.99, the flux in the sub-peak increased steadily, approximately inversely proportionally to the stellar separation, indicating that the shocked gas in the WCR where the line was formed was adiabatic. After periastron, the sub-peak flux was anomalously strong and varied rapidly, suggesting formation in clumps down-stream in the WCR. For most of the time, its flux exceeded the 2–10-keV X-ray emission, showing it to be a significant coolant of the shocked wind.

The COS Absorption Survey of Baryon Harbors: Unveiling the Physical Conditions of Circumgalactic Gas through Multiphase Bayesian Ionization Modeling

Quasar absorption systems encode a wealth of information about the abundances, ionization structure, and physical conditions in intergalactic and circumgalactic media. Simple (often single-phase) photoionization models are frequently used to decode such data. Using five discrete absorbers from the COS Absorption Survey of Baryon Harbors (CASBaH) that exhibit a wide range of detected ions (e.g., Mg ii, S ii – S vi, O ii – O vi, Ne viii), we show several examples where single-phase ionization models cannot reproduce the full set of measured column densities. To explore models that can self-consistently explain the measurements and kinematic alignment of disparate ions, we develop a Bayesian multiphase ionization modeling framework that characterizes discrete phases by their unique physical conditions and also investigates variations in the shape of the UV flux field, metallicity, and relative abundances. Our models require at least two (but favor three) distinct ionization phases ranging from T ≈ 104 K photoionized gas to warm-hot phases at T ≲ 105.8 K. For some ions, an apparently single absorption “component” includes contributions from more than one phase, and up to 30% of the H i is not from the lowest ionization phase. If we assume that all of the phases are photoionized, we cannot find solutions in thermal pressure equilibrium. By introducing hotter, collisionally ionized phases, however, we can achieve balanced pressures. The best models indicate moderate metallicities, often with sub-solar N/α, and, in two cases, ionizing flux fields that are softer and brighter than the fiducial Haardt & Madau UV background model.

A new era of fine structure constant measurements at high redshift

ABSTRACT New observations of the quasar HE0515−4414 have been made, aided by the Laser Frequency Comb (LFC), using the HARPS spectrograph on the ESO 3.6m telescope. We present three important advances for α measurements in quasar absorption spectra from these observations. First, the data have been wavelength calibrated using LFC and ThAr methods. The LFC wavelength calibration residuals are six times smaller than when using the standard ThAr calibration. We give a direct comparison between α measurements made using the two methods. Secondly, spectral modelling was performed using Artificial Intelligence (fully automated, all human bias eliminated), including a temperature parameter for each absorption component. Thirdly, in contrast to previous work, additional model parameters were assigned to measure α for each individual absorption component. The increase in statistical uncertainty from the larger number of model parameters is small and the method allows a substantial advantage; outliers that would otherwise contribute a significant systematic, possibly corrupting the entire measurement, are identified and removed, permitting a more robust overall result. The $z$abs = 1.15 absorption system along the HE0515−4414 sightline yields 40 new α measurements. We constrain spatial fluctuations in α to be Δα/α ≤ 9 × 10−5 on scales $\approx \!\! {20}\, {\rm km\, s}^{-1}$, corresponding to $\approx 25\,$kpc if the $z$abs = 1.15 system arises in a 1Mpc cluster. Collectively, the 40 measurements yield Δα/α = −0.27 ± 2.41 × 10−6, consistent with no variation.

Surprises in the simultaneous X-ray and optical monitoring of π Aquarii

To help constrain the origin of the peculiar X-ray emission of γ Cas stars, we conducted a simultaneous optical and X-ray monitoring of π Aqr in 2018. At that time, the star appeared optically bright and active, with a very strong Hα emission. Our monitoring covers three 84 d orbital cycles, allowing us to probe phase-locked variations as well as longer-term changes. In the new optical data, the radial velocity variations seem to span a smaller range than previously reported, which might indicate possible biases. The X-ray emission is variable, but without any obvious correlation with orbital phase or Hα line strength. Furthermore, the average X-ray flux and the relative range of flux variations are similar to those recorded in previous data, although the latter data were taken when the star was less bright and its disk had nearly entirely disappeared. Only the local absorption component in the X-ray spectrum appears to have strengthened in the new data. This absence of large changes in X-ray properties despite dramatic disk changes appears at odds with previous observations of other γ Cas stars. It also constrains scenarios proposed to explain the γ Cas phenomenon.

Studying the H-alpha line of the B[ e ] supergiant binary GG Carinae using high-cadence optical spectroscopy

We present a case study of GG Carinae (GG Car), a Galactic B[ e ] supergiant binary having significant eccentricity (0.28), based on Global Jet Watch spectroscopy data which has been collecting high-time-sampled optical spectra since early 2015. GG Car has so far not been observed in the X-ray band, however it is of similar phenomenology to known X-ray binaries and may therefore be an obscured X-ray source. We have discovered that the absorption component of the H-alpha line displays a ∼62-478-day period in both equivalent width and wavelength centroid indicating cycles in the dynamics of the circumstellar environment, such as precession of the circumbinary or circumprimary disk. Circumbinary disk precession is an as-of-yet underexplored origin of super-orbital variations in the X-ray flux of X-ray binaries, since the rate of precession is generally much longer than the orbital period of the inner binary.

Photothermal Determination of Absorption and Scattering Spectra of Silver Nanoparticles

This work reports on photothermal lens spectra of silver nanoparticles of different dimensions in the spectral region of 370–730 nm performed using an arc-lamp-based photothermal spectrophotometer. We show that the photothermal and extinction cross-section spectra of the samples are similar for nanoparticles of reduced dimensions where scattering effects are small. The results differ substantially for nanoparticles of a diameter larger than 30 nm for which scattering becomes relevant. We demonstrate that the photothermal spectrum corresponds to the absorption component of the particle’s extinction. Photothermal spectra show a clear picture of the plasmonic peaks of the nanoparticle even in the presence of high scattering. By subtracting the photothermal component from the total extinction, we extract the scattering cross-section spectra of the nanoparticles. The technique allows determination of the absorption and scattering components of the extinction providing a better understanding of the particle’s optical properties. The results agree well with the Mie approximation, which is valid for a single spherical nanoparticle. We discuss and demonstrate the application of the method to characterize particles of arbitrary shape and dimensions.

Probing of Carrier Recombination in n- and p-Type 6H-SiC Using Ultrafast Supercontinuum Pulses

Excess carrier dynamics in 6H-SiC substrates with n- and p-type moderate doping were detected using femtosecond pump-probe measurements with supercontinuum probing. Band-to-band recombination and carrier trapping were determined as the main recombination processes in both materials. Spectral fingerprints corresponding to each of these recombination components were obtained using the global and target analysis. It was shown that, in spite of background doping, the band-to-band recombination in 6H-SiC is dominated by the excess electron absorption component and the carrier trapping is dominated by the excess hole absorption.

Numerical Simulation Study on the Thickness of Cylinder Influencing on Energy-Absorbing Characteristics

According to the problem that the thickness change of the square cylinder as energy-absorption component affect energy-absorption characteristics of the square cylinder, this paper researches that the thickness of the square cylinder for energy-absorption component of the square cylinders influence through theoretical analysis and using numerical calculation method. The theoretical part in this paper analyze local deformation of the square cylinder theoretical model as a result of axial compression ,and in the numerical simulation part this paper simulate the dynamic response of the thin wall square cylinder model structure , thereby research the thickness change of the square cylinder influence on energy-absorption characteristics of the square cylinder. At last, the change curve of the force-deformation is drawn with the change curve of force-peak load, and it is obtained law that the thickness of the square cylinder influence on energy-absorption characteristics the square cylinder and optimum thickness.

Improved microwave absorption in lightweight resin-based carbon foam by decorating with magnetic and dielectric nanoparticles

Carbon foam (CFoam) decorated with Fe3O4–ZnO nanoparticles significantly improved electromagnetic radiation shielding effectiveness which is mainly dominated by absorption component.