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We present observations with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope (HST) of 11 Lyman continuum (LyC) leaking galaxies at redshifts, z, in the range 0.29–0.43, with oxygen abundances 12+log(O/H) = 7.64–8.16, stellar masses M⋆ ∼ 107.8–109.8 M⊙, and O32 = [O iii] λ5007/[O ii] λ3727 of ∼ 5–20 aiming to detect the C iii] λ1908 emission line. We combine these observations with the optical Sloan Digital Sky Survey (SDSS) spectra for the determination of carbon, nitrogen, and oxygen abundances. Our sample was supplemented by 31 galaxies from the literature, for which carbon, nitrogen, and oxygen abundances can be derived from the HST and SDSS spectra. These additional galaxies, however, do not have LyC observations. We find that log(C/O) for the entire sample at 12+log(O/H) 0.1, including LyC leakers, is systematically higher compared to the rest of the sample with lower metallicity. We find that log(C/O) slightly decreases with increasing M⋆ from ∼ −0.65 at M⋆ = 106 M⊙ to ∼ −0.80 at M⋆ = 109–1010 M⊙, whereas log(N/O) is considerably enhanced at M⋆ > 108 M⊙. The origin of these trends remains basically unknown. A possible solution would be to assume that the upper mass limit of the stellar initial mass function in more massive galaxies is higher. This would result in a higher production of oxygen and a larger fraction of massive stars with stellar wind polluting the interstellar medium with nitrogen.

Recently, Kojima and co-authors have reported a record low oxygen abundance, 12+logO/H=6.90+/-0.03 in the low-mass star-forming galaxy HSC J1631+4426. This exceptionally low oxygen abundance was obtained by the direct method, using the [OIII]4363 emission line. However, using the strong-line method by Izotov et al. (2019b), these authors have derived a significantly higher metallicity 12+logO/H=7.175+/-0.005. To clarify the situation, we have obtained new observations of HSC J1631+4426 with the Large Binocular Telescope (LBT)/Multi-Object Dual Spectrograph (MODS). We have derived a higher oxygen abundance, 12+logO/H=7.14+/-0.03, using the direct method, a value similar to the oxygen abundance obtained by the strong-line method. Thus, HSC J1631+4426 has a metallicity close to that of the well known blue compact dwarf galaxy IZw18., Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letters

We have studied the spectral time variations of candidate luminous blue variable stars (cLBV) in two low-metallicity blue compact dwarf galaxies, DDO 68 and PHL 293B. The LBV in DDO 68, located in HII region #3, shows an outburst, with an increase of more than 1000 times in Halpha luminosity during the period 2008-2010. The broad emission of the HI and HeI lines display a P Cygni profile, with a relatively constant terminal velocity of ~800 km/s, reaching a maximum luminosity L(Halpha) of ~2x10^38 erg/s, with a FWHM of ~1000-1200 km/s. On the other hand, since the discovery of a cLBV in 2001 in PHL 293B, the fluxes of the broad components and the broad-to-narrow flux ratios of the HI and HeI emission lines in this galaxy have remained nearly constant over 16 years, with small variations. The luminosity of the broad Halpha component varies between ~2x10^38 erg/s and ~10^39 erg/s, with the FWHM varying in the range ~500-1500 km/s. Unusually persistent P Cygni features are clearly visible until the end of 2020 despite a decrease of the broad-to-narrow flux ratio in the most recent years. A terminal velocity of ~800 km/s is measured from the P Cygni profile, similar to the one in DDO 68, although the latter is 3.7 more metal-deficient than PHL 293B. The relative constancy of the broad Halpha luminosity in PHL 293B suggests that it is due to a long-lived stellar transient of type LBV/SN IIn., Comment: 12 pages, 7 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We report the discovery of [NeV]3426 emission, in addition to HeII4686 emission, in six compact star-forming galaxies. These observations considerably increase the sample of eight such galaxies discovered earlier by our group. For four of the new galaxies, the optical observations are supplemented by near-infrared spectra. All galaxies, but one, have HII regions that are dense, with electron number densities of ~300-700 cm-3. They are all characterised by high Hbeta equivalent widths EW(Hbeta)~190-520A and high O32=[OIII]5007/[OII]3727 ratios of 10-30, indicating young starburst ages and the presence of high ionization radiation. All are low-metallicity objects with 12+logO/H=7.46-7.88. The spectra of all galaxies show a low-intensity broad component of the Halpha line and five out of six objects show Wolf-Rayet features. Comparison with photoionization models shows that pure stellar ionization radiation from massive stars is not hard enough to produce such strong [NeV] and HeII emission in our galaxies. The [NeV]3426/HeII4686 flux ratio of ~1.2 in J1222+3602 is consistent with some contribution of active galactic nucleus ionizing radiation. However, in the remaining five galaxies, this ratio is considerably lower, 20 pages, 7 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of seven compact low-mass star-forming galaxies at redshifts, z,in the range 0.3161-0.4276, with various O3Mg2=[OIII]5007/MgII 2796+2803 and Mg2=MgII 2796/MgII 2803 emission-line ratios. We aim to study the dependence of leaking Lyman continuum (LyC) emission on the characteristics of MgII emission together with the dependences on other indirect indicators of escaping ionizing radiation. LyC emission with escape fractions fesc(LyC)=3.1-4.6 per cent is detected in four galaxies, whereas only 1sigma upper limits of fesc(LyC) in the remaining three galaxies were derived. A strong narrow Ly-alpha emission line with two peaks separated by Vsep~298-592 km/s was observed in four galaxies with detected LyC emission and very weak Ly-alpha emission is observed in galaxies with LyC non-detections. Our new data confirm the tight anti-correlation between fesc(LyC) and Vsep found for previous low-redshift galaxy samples. Vsep remains the best indirect indicator of LyC leakage among all considered indicators. It is found that escaping LyC emission is detected predominantly in galaxies with Mg2>1.3. A tendency of an increase of fesc(LyC) with increasing of both the O3Mg2 and Mg2 is possibly present. However, there is substantial scatter in these relations not allowing their use for reliable prediction of fesc(LyC)., 19 pages, 11 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society. arXiv admin note: substantial text overlap with arXiv:2103.01514

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine low-mass star-forming galaxies at redshifts, z, in the range 0.3179–0.4524, with stellar masses $M_\star \, \lt $ 108 M⊙ and very high specific star-formation rates sSFR ∼150–630 Gyr−1, aiming to study the dependence of leaking Lyman continuum (LyC) emission on stellar mass and some other characteristics of the galaxy. We detect LyC emission in four out of nine galaxies with escape fractions, fesc(LyC), in the range of 11–35 per cent, and establish upper limits for fesc(LyC) in the remaining five galaxies. We observe a narrow Ly α emission line with two peaks in seven galaxies and likely more complex Ly α profiles in the two remaining galaxies. The velocity separation between the peaks Vsep varies in the range from ∼229 to ∼512 km s−1. Our additional data on low-mass galaxies confirm and strengthen the tight anticorrelation between fesc(LyC) and Vsep found for previous low-redshift galaxy samples with higher stellar masses. Vsep remains the best indirect indicator of LyC leakage. It is better than O32 on which fesc(LyC) depends weakly, with a large scatter. Finally, contrary to expectations, we find no increase of fesc(LyC) with decreasing galaxy stellar mass M⋆.

Physical characteristics of a large sample of compact galaxies with active star formation from the SDSS DR14 are derived. The sample includes approximately 30 000 compact isolated galaxies with angular diameters

Structural data and dependences of the film resistance on magnetic field strength R(H) are presented for Co–Gd and Al–Co–Gd alloy films obtained by vacuum sputtering. It has been found that amorphous Co55Gd45 films show ferromagnetism at room temperature. Singularities observed in the run of R(H) curves for Al84Co8Gd8 and Al92Co6Gd2 films are associated with magnetic ordering in the films.

Integrated characteristics of a sample of 66 star-forming galaxies with extremely low oxygen abundances from the SDSS Data Release 14 are studied. The oxygen abundances were determined by the direct Te method for 42 galaxies with detected [O III] 436.3 nm emission lines and by the strong-line method for the remaining galaxies. Derived abundances 12 + log (O/H) fall within the 6.97–7.52 range and are, on average, four times lower than the corresponding values for a large comparison sample of compact star-forming galaxies from the SDSS. Stellar masses and Hβ luminosities for both samples were derived from SDSS spectra with a small spectroscopic aperture (2–3 arcsec in diameter). In order to determine their values for the entire galaxy, aperture corrections taking radiation outside the spectroscopic slit into account were introduced. Stellar masses and luminosities in the optical range are 100 times lower than the corresponding values for the galaxies from the comparison sample. At fixed values of luminosity and stellar mass, these galaxies have lower oxygen abundances in the oxygen abundance–luminosity and oxygen abundance–stellar mass diagrams than the galaxies from the main SDSS sample. This offset is likely caused by accretion of unenriched intergalactic gas, which reduces the oxygen abundance in the galactic interstellar medium. The majority of galaxies with extremely low oxygen abundances were detected in the mid-infrared range by the WISE space telescope. Color index W1 – W2, where W1 and W2 are the magnitudes at a wavelength of 3.4 and 4.6 μm, of these galaxies corresponds to the values typical for stellar emission and/or free-free ionized gas emission. The low ultraviolet luminosity, which is the main source of dust heating in star-forming galaxies, thus eliminates the possibility that warm and hot dust is present.

Kinetic instabilities in a dense plasma of a continuous ECR discharge in a mirror magnetic trap at the GISMO setup are studied. We experimentally define unstable regimes and corresponding plasma parameters, where the excitation of electromagnetic emission is observed, accompanied by the precipitation of energetic electrons from the magnetic trap. Comprehensive experimental study of the precipitating electron energy distribution and plasma electromagnetic emission spectra, together with theoretical estimates of the cyclotron instability increment proves that under the experimental conditions the observed instability is related to the excitation of whistler-mode waves, which are a driver of losses of energetic electrons from the magnetic trap. The results of this study are important for the further development of the GISMO ECRIS facility and for the improvement of its parameters as an ion source. Also, this research of plasma kinetic instabilities is of fundamental interest and provides experimental tools to simultaneously study plasma electromagnetic activity and corresponding changes in a resonant electron energy distribution., Comment: 9 pages, 9 figures, submitted to Physics of Plasmas

A comprehensive study is made of the properties of samples of BiFe1−xMnxO3 (0.05 ≤ x ≤ 0.15) solid solutions synthesized using the sol-gel technique. Stabilization of the main phase, a reduction in the average granule size, and an increase in the dielectric constant are observed upon an increase in concentration x. The presence of Mn ions in BiFe1−xMnxO3 solid solutions results in semiconductor-type conductivity and the emergence of magnetic ordering at 605 K (х = 0.05) and 550 K (х = 0.15).

—Samples of a diamond blend (DB) are processed in supercritical isopropanol using a specially designed unit, and the IR spectra, Raman spectra, and X-ray diffraction data before and after processing are analyzed. It is shown that a noticeable decrease in the intensity of the IR absorption bands of the oxygen-containing bonds is observed as a result of this process, which is indicative of the effective etching of the shell of diamond crystallites during processing. A noticeable increase is found in the half-width of the diamond line in the Raman spectra of the samples subjected to processing, which is determined by the decrease in the dimensions of diamond nanocrystallites due to the etching of the surface defect layer. The proposed method has significant advantages over a traditional acid-based technology of purification of a diamond blend and indicates the prospect of practical application for this process.

We study the mid-infrared photometric properties of a sample of compact star-forming galaxies from the SDSS Data Release 14. The sample includes about 30 000 galaxies. The Hβ emission lines with equivalent widths EW(Hβ) > 1 nm are observed in the spectra of all selected galaxies. The selected galaxies are compact objects with angular diameters less than 6 arcsec. About 10 000 galaxies were detected by the WISE space telescope at wavelengths of 3.4 and 4.6 μm. A considerable number of galaxies was also detected at wavelengths of 12 and 22 μm. Using these data and the results of observations obtained in the ultraviolet range with the GALEX space telescope, it was shown that the heating of dust in the sample of galaxies is caused by the ultraviolet radiation of massive stars in the star-forming regions. The stellar and ionized-gas emission dominates at wavelengths of 3.4 and 4.6 μm in a majority of galaxies, whereas the dust emission dominates at wavelengths of 12 and 22 μm. In some galaxies with high Hβ luminosity, dust emission is observed even at the short wavelength of 3.4 μm, and it has a steep increase in the intensity toward the wavelength of 4.6 μm. This emission is characterized by “red” color (W1 – W2 > 2m), where W1 and W2 are magnitudes at wavelengths of 3.4 and 4.6 μm, respectively. The probable cause of this emission is the presence of hot dust with a temperature of hundreds of Kelvins. A list of 39 galaxies with such an extremely high W1 – W2 color index is presented.

Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3−7327 were recently taken as part of the Early Release Observations (EROs) program of the James Webb Space Telescope (JWST). Among these, two NIRSpec spectra of galaxies, at z = 7.7 and at z = 8.5, were obtained, revealing, for the first time, the rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the important [O III]λ4363 auroral line (see JWST PR 2022-035). We present an analysis of the emission line properties of these galaxies, finding that these galaxies have a high excitation (as indicated by high ratios of [O III]λ5007/[O II] λ3727, [Ne III] λ3869/[O II] λ3727), strong [O III]λ4363, high equivalent widths, and other properties typical of low-metallicity star-forming galaxies. Using the direct method, we determined oxygen abundances of 12 + log(O/H)≈7.9 in two z = 7.7 galaxies and a lower metallicity of 12 + log(O/H)≈7.4 − 7.5 (∼5% solar) in the z = 8.5 galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from spectral energy distribution (SED) fits, we find that the three galaxies lie close to or below the z ∼ 2 mass-metallicity relation. Overall, these first galaxy spectra at z ∼ 8 show a strong resemblance in their the emission line properties of galaxies in the epoch of reionization with those of relatively rare local analogs previously studied with the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal the properties of galaxies in the early Universe.

Using the Large Binocular Telescope (LBT)/Multi-Object Dual Spectrograph (MODS), we have obtained optical spectroscopy of one of the most metal-poor dwarf star-forming galaxies (SFG) in the local Universe, J2229+2725. This galaxy with a redshift z=0.0762 was selected from the Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS). Its properties derived from the LBT observations are most extreme among SFGs in several ways. Its oxygen abundance 12+logO/H=7.085+/-0.031 is among the lowest ever observed for a SFG. With its very low metallicity, an absolute magnitude Mg=-16.39 mag, a low stellar mass Mstar=9.1x10^6 Msun and a very low mass-to-light ratio Mstar/Lg~0.0166 (in solar units), J2229+2725 deviates strongly from the luminosity-metallicity relation defined by the bulk of the SFGs in the SDSS. J2229$+$2725 has a very high specific star-formation rate sSFR~75 Gyr^-1, indicating very active ongoing star formation. Three other features of J2229+2725 are most striking, being the most extreme among lowest-metallicity SFGs: 1) a ratio O32=I([OIII]5007)/I([OII]3727)~53, 2) an equivalent width of the Hbeta emission line EW(Hbeta) of 577A, and 3) an electron number density of ~1000 cm^-3. These properties imply that the starburst in J2229+2725 is very young. Using the extremely high O32 in J2229+2725, we have improved the strong-line calibration for the determination of oxygen abundances in the most metal-deficient galaxies, in the range 12 + logO/H, 10 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society. arXiv admin note: text overlap with arXiv:1812.07917

We compare the relations among various integrated characteristics of ~25,000 low-redshift (z1.5) star-forming galaxies (SFGs) with respect to oxygen abundances, stellar masses M*, far-UV absolute magnitudes M(FUV), star-formation rates SFR and specific star-formation rates sSFR, Lyman-continuum photon production efficiencies (xi_ion), UV continuum slopes \beta, [OIII]5007/[OII]3727 and [NeIII]3868/[OII]3727 ratios, and emission-line equivalent widths EW([OII]3727), EW([OIII]5007), and EW(H\alpha). We find that the relations for low-z CSFGs with high equivalent widths of the H\beta emission line, EW(H\beta)>100A, and high-z SFGs are very similar, implying close physical properties in these two categories of galaxies. Thus, CSFGs are likely excellent proxies for the SFGs in the high-z Universe. They also extend to galaxies with lower stellar masses, down to ~10^6 Msun, and to absolute FUV magnitudes as faint as -14 mag. Thanks to their proximity, CSFGs can be studied in much greater detail than distant SFGs. Therefore, the relations between the integrated characteristics of the large sample of CSFGs studied here can prove very useful for our understanding of high-z dwarf galaxies in future observations with large ground-based and space telescopes., Comment: 20 pages, 14 figures, accepted for publication in Astronomy and Astrophysics

To ensure further progress in the development of electron cyclotron resonance ion sources (ECRISs), deeper understanding of the underlying physics is required. The electron energy distribution (EED), which is crucial for the performance of an ECRIS, still remains obscure. The present paper focuses on the details of a well-developed technique of measuring the EED of electrons escaping axially from the magnetically confined plasma of an ECRIS. The method allows for better than 500 eV energy resolution over a range of electron energies from 4 keV to over 1 MeV. We present detailed explanation of the experimental procedure and the following data processing peculiarities with examples and discuss possible reasons of energetic electron losses from the magnetic trap, in particular the role of RF pitch angle scattering. Finally, an experimental method of approximating the confined EED based on the measurement of escaping electrons is described.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Context. Finding and elucidating the properties of Lyman-continuum(LyC)-emitting galaxies is an important step in improving our understanding of cosmic reionization. Aims. Although the z ∼ 0.3 - 0.4 LyC emitters found recently show strong optical emission lines, no consistent quantitative photoionization model taking into account the escape of ionizing photons and inhomogenous interstellar medium (ISM) geometry of these galaxies has yet been constructed. Furthermore, it is unclear to what extent these emission lines can be used to distinguish LyC emitters. Methods. To address these questions we construct one- and two-zone photoionization models accounting for the observed LyC escape, which we compare to the observed emission line measurements. The main diagnostics used include lines of [O III], [O II], and [O I] plus sulfur lines ([S II], [S III]) and a nitrogen line ([N II]), which probe regions of different ionization in the ISM. Results. We find that single (one-zone) density-bounded photoionization models cannot reproduce the emission lines of the LyC leakers, as pointed out by earlier studies, because they systematically underpredict the lines of species of low ionization potential, such as [O I] and [S II]. Introducing a two-zone model, with differing ionization parameter and a variable covering fraction and where one of the zones is density-bounded, we show that the observed emission line ratios of the LyC emitters are well reproduced. Furthermore, our model yields LyC escape fractions, which are in fair agreement with the observations and independent measurements. The [O I] λ6300 excess, which is observed in some LyC leakers, can be naturally explained in this model, for example by emission from low-ionization and low-filling-factor gas. LyC emitters with a high escape fraction (fesc 38%) are deficient both in [O I] λ6300 and in [S II] λλ6716,6731. We also confirm that a [S II] λλ6716,6731 deficiency can be used to select LyC emitter candidates, as suggested earlier. Finally, we find indications for a possible dichotomy in terms of escape mechanisms for LyC photons between galaxies with relatively low (fesc 10%) and higher escape fractions. Conclusions. We conclude that two-zone photoionization models are sufficient and required to explain the observed emission line properties of z ∼ 0.3 - 0.4 LyC emitters. This is in agreement with UV absorption line studies, which also show the co-existence of regions with high hydrogen column density (i.e., no escape of ionizing photons) and density-bounded or very low column density regions responsible for the observed escape of LyC radiation. These simple but consistent models provide a first step towards the use of optical emission lines and their ratios as quantitative diagnostics of LyC escape from galaxies. © L. Ramambason et al. 2020., YII and NGG acknowledge support from the National Academy of Sciences of Ukraine by its priority project No.0120U100935 “Fundamental properties of the matter in the relativistic collisions of nuclei and in the early Universe”. JMV acknowledges support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the IAA (SEV-2017-0709) and project AYA2016-79724-C4-4-P. RA acknowledges support from FONDECYT Regular Grant 1202007.

The article discusses the formation of the polished film on the collector, its composition, and describes the causes of “burnings” on the collector and ways to eliminate them by installing a composite grinding insert. The aim of the present study is to investigate the feasibility of guidance of the polished film on the collector of the starter-generator by reducing the pressure on the current-carrying brushes, and to measure the resistance of the polished film, the brush wear and the collector. The characteristics of the starter-generator are studied at various pressures on current carrying brushes. The acceptance checkouts are carried out. The use of reduced pressure springs made it possible to accelerate the process of forming the polished film by 1.5 times. The resource of current-carrying brushes and the collector increases. The decrease in pressure allows reducing mechanical losses in the collector-and-brush assembly unit and increasing the efficiency of the starter-generator.

Identifying the mechanisms driving the escape of Lyman Continuum (LyC) photons is crucial to find Lyman Continuum Emitter (LCE) candidates. To understand the physical properties involved in the leakage of LyC photons, we investigate the connection between the HI covering fraction, HI velocity width, the Lyman alpha (LyA) properties and escape of LyC photons in a sample of 22 star-forming galaxies including 13 LCEs. We fit the stellar continua, dust attenuation, and absorption lines between 920 and 1300 A to extract the HI covering fractions and dust attenuation. Additionally, we measure the HI velocity widths of the optically thick Lyman series and derive the LyA equivalent widths (EW), escape fractions (fesc), peak velocities and fluxes at the minimum of the LyA profiles. Overall, we highlight strong correlations between the presence of low HI covering fractions and (1) low LyA peak velocities; (2) more flux at the profile minimum; and (3) larger EW(LyA), fesc(LyA), and fesc(LyC). Hence, low column density channels are crucial ISM ingredients for the leakage of LyC and LyA photons. Additionally, galaxies with narrower HI absorption velocity widths have higher LyA equivalent widths, larger LyA escape fractions, and lower LyA peak velocity separations. This suggests that these galaxies have low HI column density. Finally, we find that dust regulates the amount of LyA and LyC radiation that actually escapes the ISM. Overall, the ISM porosity is one origin of strong LyA emission and enables the escape of ionizing photons in low-z leakers. However, this is not enough to explain the largest fesc(LyC) observed, which indicates that the most extreme LCEs are likely density-bounded along all lines of sight to the observer. Overall, the neutral gas porosity constrains a lower limit to the escape fraction of LyC and LyA photons, providing a key estimator of the leakage of ionizing photons., Comment: Accepted for publication in A&A. 28 pages, 23 figures, 7 tables

Using new Very Large Telescope (VLT)/XShooter spectral observations we analyse the physical properties of five z similar to 0.3-0.4 confirmed Lyman continuum (LyC) leakers. Strong resonant MgII lambda lambda 2796, 2803 angstrom emission lines (I(lambda lambda 2796, 2803)/I(H beta) similar or equal to 10-38 per cent) and non-resonant Fe II* lambda lambda 2612, 2626 angstrom emission lines are observed in spectra of five and three galaxies, respectively. We find high electron densities N-e similar to 400 cm(-3), significantly higher than in typical low-z, but comparable to those measured in z similar to 2-3 star-forming galaxies (SFGs). The galaxies have a mean value of log N/O = -1.16, close to the maximum values found for SFGs in the metallicity range of 12 + logO/H similar or equal to 7.7-8.1. All 11 low-z LyC emitting galaxies found by Izotov et al., including the ones considered in this study, are characterized by high equivalent width (EW) (H beta) similar to 200-400 angstrom, high ionization parameter (log(U) = -2.5 to -1.7), high average ionizing photon production efficiency xi = 10(25.54) Hz erg(-1), and hard ionizing radiation. On the Baldwin-Phillips-Terlevich (BPT) diagram we find the same offset of our leakers from low-z main-sequence SFGs as that for local analogues of Lyman-break galaxies (LBGs) and extreme SFGs at z similar to 2-3. We confirm the effectiveness of the He I emission lines diagnostics proposed by Izotov et al. in searching for LyC leaker candidates and find that their intensity ratios correspond to those in a median with low neutral hydrogen column density N(H I) = 10(17)-5 x 10(17) cm(-2) that permit leakage of LyC radiation, likely due to their density-bounded HII regions. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, NGG and YII acknowledge support from the National Academy of Sciences of Ukraine by its priority project `Fundamental properties of the matter in the relativistic collisions of nuclei and in the early Universe' (No. 0120U100935). JMV, EP-M, JI-P, and CK acknowledge financial support from the StateAgency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award to the Instituto de Astrofisica de Andaluc ' ia (SEV-2017-0709) and project A2016-79724-C4-4-P. RA acknowledges support from FONDECYT Regular 1202007. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is www.sdss.org.SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

The factors of increased wear of current-carrying brushes in direct-current motors designed for high-altitude operation are considered. The results of testing six motors with different degrees of airtightness are presented. It is found out that increased airtightness makes the lacquer film less resistive (thinner) and increases the brush wear. A method of decreasing the wear of current-carrying brushes at standard and high altitudes is proposed that consists in installing a DMS-140 molybdenum disulfide lubricating brush. The lubricating brush is installed in an auxiliary brush holder or in a pocket structurally connected with the current-carrying brush holder on the header runway. The effect of the collector profile material (copper, cadmium bronze, chromium bronze) on the wear of current-carrying brushes is studied, as well as the efficiency of installing lubricating brushes for standard and high-altitude operations. The effect of lubricating brushes on the performance of a 5-W motor is considered as well as the results of testing seven 5-W motors equipped with lubricating brushes in conformity with the machine and warranty service specifications. Information is given on the results of long-term storage (for 1 and 1.9 years) of four motors with different capacities equipped with lubricating brushes, as well as in thermal vacuum tests of 10-W motors under p = 10–5–10–6 mm Hg.

We present Large Binocular Telescope spectrophotometric observations of five low-redshift (z, 16 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We derive apparent and absolute ultraviolet (UV) magnitudes, and luminosities in the infrared (IR) range of a large sample of low-redshift (0, Comment: 14 pages, 12 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

A way of reducing irregular current distribution in multi-brush systems of sliding current transfer with its wear reduction due to installing lubricating molybdenum disulphide brushes on slip rings to ensure a greasing nano-sized cover on the slip ring surface is proposed. The authors give the results of industrial tests estimated on the performance effectiveness of lubricating brushes on slip rings of the TBB-320-2UZ-type turbine generator. The results showed that the lubricating brushes reduce a) the wear of 6110 OM+M and EG2AF+M brushes by 1.2 and 2.1 times respectively, b) current distribution irregularity in parallel operating brushes due to stabilizing the contact arc, and c) the temperature of the electrical brush-contact device due to the friction reduction in brushes.

Interactions and mergers between dwarf galaxies are mostly gas-rich and should be marked by an intense star formation activity. But these processes, which are expected to be common at earlier times, are very difficult to observe at low redshifts. To investigate that, we look in the Sloan Digital Sky Survey (SDSS) for compact groups that contain one luminous compact galaxy (LCG) with very high specific star formation rate (sSFR) and at least two other blue galaxies. We found 24 groups that satisfy these criteria, among which 12 groups have SDSS spectroscopic data for at least 2 member galaxies. Here we want to investigate, using the tidal strength estimator Q, how interactions between neighbouring galaxies affect the sSFR and concentration of each LCG. Statistical tests reveal a correlation between Q and their sSFR, indicating that tidal forces between neighbouring galaxies might be inducing bursts of star formation in the LCGs.

Electric machines are widely used in the assembly, and mechanisms of modern equipment and devices operate in different climatic conditions. These conditions often determine the peculiarities of operation of electric machines, repair and preventive measures. In many ways, the reliability of DC electric machines is determined by the node of a sliding current collector (UST), in which the current-carrying brushes are in dynamic and static contact with the plates of the metal collector or ring. Physical, mechanical, and chemical processes occurring at the interface of the contacting counterbody data determine the switching processes and reliability (UST). The purpose of the article is to analyze and study the impact of probable physical and chemical factors on the operational reliability of the sliding current collector unit of electric machines. The results of scientific and practical work allow determining the measures aimed at eliminating the negative impact of adverse physical and chemical environmental factors on electric machines.

Understanding the ionizing spectrum of low-metallicity galaxies is of great importance for modeling and interpreting emission line observations of early/distant galaxies. Although a wide suite of stellar evolution, atmosphere, population synthesis, and photoionization models, taking many physical processes into account now exist, all models face a common problem: the inability to explain the presence of nebular HeII emission, which is observed in many low metallicity galaxies, both in UV and optical spectra. Several possible explanations have been proposed in the literature, including Wolf-Rayet (WR) stars, binaries, very massive stars, X-ray sources, or shocks. However, none has so far been able to explain the major observations. We briefly discuss the HeII problem, available empirical data, and observed trends combining X-ray, optical and other studies. We present a simple and consistent physical model showing that X-ray binaries could explain the long-standing nebular HeII problem. Our model, described in Schaerer et al. (2019), successfully explains the observed trends and strength of nebular HeII emission in large samples of low metallicity galaxies and in individual galaxies, which have been studied in detail and with multi-wavelength observations. Our results have in particular important implications for the interpretation of galaxy spectra in the early Universe, which will be obtained with upcoming and future facilities., 5 pages, 2 figures. Proceedings of IAU Symposium No. 352, 2019 "Uncovering early galaxy evolution in the ALMA and JWST era". Eds. E. da Cunha, J. Hodge, J. Afonso, L. Pentericci

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of eight compact star-forming galaxies at redshifts z=0.02811-0.06540, with low oxygen abundances 12+log(O/H)=7.43-7.82 and extremely high emission-line flux ratios O32=[OIII]5007/[OII]3727~22-39, aiming to study the properties of Ly-alpha emission in such conditions. We find a diversity in Ly-alpha properties. In five galaxies Ly-alpha emission line is strong, with equivalent width (EW) in the range 45-190A. In the remaining galaxies, weak Ly-alpha emission with EW(Ly-alpha)~2-7A is superposed on a broad Ly-alpha absorption line, indicating a high neutral hydrogen column density N(HI)~(1-3)x10^21 cm^-2. We examine the relation between the Ly-alpha escape fraction fesc(Ly-alpha) and the Lyman continuum escape fraction fesc(LyC), using direct measures of the latter in eleven low-redshift LyC leakers, to verify whether fesc(Ly-alpha) can be an indirect measure of escaping LyC radiation. The usefulness of O32, of the Ly-alpha equivalent width EW(Ly-alpha) and of the Ly-alpha peak separation Vsep as indirect indicators of Ly-alpha leakage is also discussed. It is shown that there is no correlation between O32 and fesc(Ly-alpha). We find an increase of fesc(Ly-alpha) with increasing EW(Ly-alpha) for EW(Ly-alpha)150A the fesc(Ly-alpha) is nearly constant attaining the value of ~0.25. We find an anticorrelation between fesc(Ly-alpha) and Vsep, though not as tight as the one found earlier between fesc(LyC) and Vsep. This finding makes Vsep a promising indirect indicator of both the Ly-alpha and ionizing radiation leakage., 17 pages, 9 figures, 7 tables, accepted for publication in MNRAS

The article analyzes the reasons for the increased wear of the brushes of the starter-generator GS-12TOK, caused by the peculiarity of its mode of operation. The authors of the article have investigated how sparking has influenced transitional processes “throwing the load - dropping the load” on the resistance of the polished film. Sparking leads to its disturbance and an increase in the wear of brushes. The authors have proposed a method for accelerating the formation of the polished film in multi-brush systems due to the inclusion of brushes with a high rate of formation of the polished film in the current transmission system. Flight tests and equivalent cyclic resource bench tests have been conducted. The generator equipped with the EG-61A polish-forming brushes (impregnated) with normal pressure on all brushes provides an increase in the service life of the current-carrying brushes by more than two times without increasing the rate of formation of the polished film. The generator with EG-61A polish-forming brushes (not impregnated) with a pressure on all brushes of 500-550g provides an increase in the resource of brushes up to five times with an increase in the rate of formation of the polished film. It is recommended for mass production.