Improving the method for identifying the source of excess emissions based on mobile laboratory data

The article highlights an environmental problem that is relevant for industrial cities, namely the identification of the source of excess emissions. The existing monitoring systems are not designed to identify sources that are violators, and the Supervisory authorities currently lack not only a tool, but also an algorithm for identifying the violator when determining excess pollution levels. The article considers current methods and devices aimed at locating a source that has allowed an excess emission, but all of them have their own disadvantages and limitations. The article presents a method for identifying the source of excess emission based on air sampling conducted by mobile laboratories. The proposed method was tested on mobile laboratory data obtained during an atmospheric air survey in the Soviet administrative district of Omsk. The results of the estimated emission power, determining the multiplicity of excess for each of the considered sources, and identifying the most likely source that allowed an excess emission are presented. Locations have also been identified for confirming windward and leeward sampling from the suspected offending source. The developed method is based on the use of a method approved in Russia for calculating the dispersion of pollutants, which makes it possible to use the results obtained by Supervisory environmental authorities as an evidence base for specific sources of pollution.

RW Aur B: a modest UX Ori-type companion of the famous primary

ABSTRACT The secondary of the famous young binary RW Aur is much less studied than the primary. To rectify this shortcoming, we present here the results of UBVRIJHK photometric, VRI polarimetric and optical spectral observations of RW Aur B. The star demonstrates chaotic brightness variations in the optical band, with irregular, short (∼1-d) dimmings with an amplitude ΔV up to 1.3 mag. The dimmings are accompanied by an increase in the linear polarization (up to 3 per cent in the I band), presumably as a result of the scattering of stellar radiation by dust in the circumstellar disc, which means that RW Aur B can be classified as a UX Ori-type star. We conclude that the observed excess emission at λ ≲ 0.45 μm and longwards of ~2 μm as well as the variability of fluxes and profiles of the H i, He i and Na i D emission lines are due to the accretion process. At the same time, emission components of Ca ii lines indicate that RW Aur B has a powerful chromosphere. Assuming solar elemental abundances, we find the following parameters for the star: Teff = 4100–4200 K, AV = 0.6 ± 0.1 (out of the dimming events), L* ≈ 0.6 ${\rm L}_\odot ,\, R_* \approx 1.5$ ${\rm R}_\odot ,\, M\approx 0.85$ M$_\odot ,\, \dot{M}_{\rm acc}\lt 5\times 10^{-9}$ M⊙ yr−1. Finally, we discuss possible reasons for the different levels of accretion activity of the RW Aur binary components and present arguments in favour of the fact that the components are gravitationally bound.

The soft state of the black hole transient source MAXI J1820+070: emission from the edge of the plunge region?

ABSTRACT The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as XMM–Newton and Chandra, but was well observed by photon-counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array(NuSTAR). We report here on the discovery of an excess-emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is $8\, {\rm M}_{\odot }$). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.

A spectral stacking analysis to search for faint outflow signatures in z ∼ 6 quasars

Aims. Outflows in quasars during the early epochs of galaxy evolution are an important part of the feedback mechanisms that potentially affect the evolution of the host galaxy. However, systematic millimetre (mm) observations of outflows are only now becoming possible with the advent of sensitive mm telescopes. In this study we used spectral stacking methods to search for a faint high-velocity outflow signal in a sample of [C II] detected, z ∼ 6 quasars. Methods. We searched for broad emission line signatures from high-velocity outflows for a sample of 26 z ∼ 6 quasars observed with the Atacama Large Millimeter Array (ALMA), with a detection of the [C II] line. The observed emission lines of the sources are dominated by the host galaxy, and outflow emission is not detected for the individual sources. We used a spectral line stacking analysis developed for interferometric data to search for outflow emission. We stacked both extracted spectra and the full spectral cubes. We also investigated the possibility that only a sub-set of our sample contributes to the stacked outflow emission. Results. We find only a tentative detection of a broad emission line component in the stacked spectra. When taking a region of about 2″ around the central position of the stacked cubes, the stacked line shows an excess emission due to a broad component of 1.1–1.5σ, but the significance drops to 0.4–0.7σ when stacking the extracted spectra from a smaller region. The broad component can be characterised by a line width of full width at half-maximum FWHM > 700 km s−1. Furthermore, we find a sub-sample of 12 sources, the stack of which maximises the broad component emission. The stack of this sub-sample shows an excess emission due to a broad component of 1.2–2.5σ. The stacked line of these sources has a broad component of FWHM > 775 km s−1. Conclusions. We find evidence suggesting the presence of outflows in a sub-sample of 12 out of 26 sources, which demonstrates the importance of spectral stacking techniques in tracing faint signal in galaxy samples. However, deeper ALMA observations are necessary to confirm the presence of a broad component in the individual spectra.

Near-infrared observations of dusty white dwarfs

AbstarctPlanetary material in the atmospheres of white dwarfs is thought to be scattered inwards from outer planetary systems. Dusty emission in the infrared traces the accretion. As the scattering of many small asteroids is a stochastic process, variability in the infrared emission is predicted. We report a 3 year near-infrared (J, H and K) monitoring campaign of 34 dusty, polluted white dwarfs which aims to search for dust emission variability. We find all white dwarfs have consistent near-infrared fluxes, implying the excess emission is stable. This suggests tidal disruption events which lead to large variabilities are rare and quick (<1 year) and become stable within a few years. For WD 0408–041, the system that shows both increases and decreases in dust emission over 11 years, our K band data suggest a potential colour change associated with the dust emission that needs further confirmation.

HST spectra reveal accretion in MY Lupi

The mass accretion rate is a crucial parameter for the study of the evolution of accretion discs around young low-mass stellar and substellar objects (YSOs). We revisit the case of MY Lup, an object where VLT/X-shooter data suggested a negligible mass accretion rate, and show it to be accreting on a level similar to other Class II YSOs in Lupus based on Hubble Space Telescope (HST) observations. In our HST-Cosmic Origins Spectrograph (HST-COS) and -Space Telescope Imaging Spectrograph (HST-STIS) spectra, we find many emission lines, as well as substantial far-ultraviolet (FUV) continuum excess emission, which can be ascribed to active accretion. The total luminosity of the C IV λ1549 Å doublet is 4.1 × 10−4 L⊙. Using scalings between accretion luminosity, Lacc, and C IV luminosity from the literature, we derive Lacc ~2 × 10−1 L⊙, which is more than an order of magnitude higher than the upper limit estimated from the X-shooter observations. We discuss possible reasons for the X-shooter-HST discrepancy, the most plausible being that the low contrast between the continuum excess emission and the photospheric+chromospheric emission at optical wavelengths in MY Lup hampered detection of excess emission. The luminosity of the FUV continuum and C IV lines, strong H2 fluorescence, and a “1600 A Bump” place MY Lup in the class of accreting objects with gas-rich discs. So far, MY Lup is the only peculiar case in which a significant difference between the HST and X-shooter Ṁacc estimates exists that is not ascribable to variability. The mass accretion rate inferred from the revisited Lacc estimate is Ṁacc ~ 1(−0.5+1.5) × 10−8 M⊙ yr−1. This value is consistent with the typical value derived for accreting YSOs of similar mass in Lupus and points to less clearing of the inner disc than indicated by near- and mid-infrared observations. This is confirmed by Atacama Large Millimeter Array (ALMA) data, which show that the gaps and rings seen in the sub-millimetre are relatively shallow.

A statistically significant lack of debris discs in medium separation binary systems

We compile a sample of 341 binary and multiple star systems with the aim of searching for and characterizing Kuiper belt-like debris discs. The sample is assembled by combining several smaller samples studied in previously published work with targets from two unpublished Herschel surveys. We find that 38 systems show excess emission at 70 or 100 $\mu$m suggestive of a debris disc. While nine of the discs appear to be unstable to perturbations from their host binary based on a simple analysis of their inferred radii, we argue that the evidence for genuine instability is not strong, primarily because of uncertainty in the true disc radii, uncertainty in the boundaries of the unstable regions, and orbital projection effects. The binary separation distributions of the disc-bearing and disc-free systems are different at a confidence level of $99.4{{\ \rm per\ cent}}$, indicating that binary separation strongly influences the presence of detectable levels of debris. No discs are detected for separations between ∼25 and 135 au; this is likely a result of binaries whose separations are comparable with typical disc radii clearing out their primordial circumstellar or circumbinary material via dynamical perturbations. The disc detection rate is $19^{+5}_{-3}{{\ \rm per\ cent}}$ for binaries wider than 135 au, similar to the published results for single stars. Only $8^{+2}_{-1}{{\ \rm per\ cent}}$ of systems with separations below 25 au host a detectable disc, which may suggest that planetesimal formation is inhibited in binaries closer than a few tens of au, similar to the conclusions of studies of known planet-hosting binaries.

Plasma injection into a solar coronal loop

Context. The details of the spectral profiles of extreme UV emission lines from solar active regions contain key information for investigating the structure, dynamics, and energetics of the solar upper atmosphere. Aims. We characterize the line profiles not only through the Doppler shift and intensity of the bulk part of the profile. More importantly, we investigate the excess emission and asymmetries in the line wings to study twisting motions and helicity. Methods. We used a raster scan of the Interface Region Imaging Spectrograph (IRIS) in an active region. We concentrated on the Si IV line at 1394 Å, which forms just below 0.1 MK, and followed the plasma that moves in a cool loop from one footpoint to the other. We applied single-Gaussian fits to the line core, determined the excess emission in the red and blue wings, and derived the asymmetry of the red and blue wings. Results. The blue wing excess at one footpoint shows injection of plasma into the loop that then flows to the other side. At the same footpoint, redshifts in the line core indicate that energy is deposited at around 0.1 MK. The enhanced pressure would then push the cool plasma down and inject some plasma into the loop. In the middle part of the loop, the spectral tilts of the line profiles indicate that the magnetic field has a helical structure, and the line wings are symmetrically enhanced. This is an indication that the loop is driven through the injection of helicity at the loop feet. Conclusions. If the loop is driven to be helical, then the magnetic field can be expected to be in a turbulent state, as has been shown by existing magnetohydrodynamics models. The turbulent motions might explain the (symmetric) line wing enhancements that have also been seen in loops at coronal temperatures, but are not understood so far.