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We present a simple one-dimensional iterative kinetic model of the cathode sheath region of high voltage, low-pressure hydrogen hollow cathode discharge. The model's convenience as a supplemental diagnostic tool is demonstrated by determining the most relevant discharge parameters through an analysis of the spectral shape of the hydrogen Balmer alpha line recorded along the axis of a cylindrically symmetrical high voltage low-pressure hollow cathodeglow discharge in hydrogen. Thus, an effectively one-dimensional approach is tested and shown to give satisfactory spectral lines fits with reasonable values for discharge parameters, most notably the gas temperature. [ABSTRACT FROM AUTHOR]

The recent observations by Fermi large area telescope (Fermi-LAT) showed that in addition to the radio galaxies and blazars, Narrow-Line Seyfert 1 (NLSy1) galaxies are also γ -rays emitters. NLSy1 are AGNs with optical spectral properties similar to those of Seyfert 1 galaxies, except for having narrow Balmer lines and strong optical lines. They also exhibit strong X-ray variability, steep X-ray spectra and relatively high luminosity. The multiwavelength emission properties of 1H 0323+342, SBS 0846+513 and PMN J0948+0022 are discussed, using the γ -ray data from the last 8.8 years Fermi-LAT observations as well as available Swift(UVOT/XRT) data. It is shown that one-zone synchrotron/synchrotron self-Compton (SSC) model can satisfactorily reproduce their observed broadband spectra. [ABSTRACT FROM AUTHOR]

Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For Hα, Hβ, and Hγ we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for Hγ, while the inner wings can be weaker in 3D models, particularly for Hα. For Hα, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (Teff ≈ 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (Teff ≈ 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from Hα, Hβ, and Hγ; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1σ uncertainties. For Hα, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of Hα can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations. [ABSTRACT FROM AUTHOR]

In plasmas coupled to an external energy source like a beam of energetic electrons, one can observe the non‐linear coupling of Langmuir waves with ion sound and electromagnetic waves. This non‐linear interaction of waves changes the structural and radiative properties of plasmas. Coherent wave packets are trapped in regions of high intensity, and are subjected to a wave collapse cycle. We show that the electric field of the wave packets can modify the spectral lines emitted by hydrogen atoms. Our model for this field is a sequence of envelope solitons oscillating at the plasma frequency or the upper hybrid frequency. The calculations presented concern the Hα and Hβ Balmer lines of hydrogen and show the possible modifications of the line shapes if wave collapse conditions affect the edge plasma. [ABSTRACT FROM AUTHOR]

We discuss the rest-frame ultraviolet (UV) emission line spectra of a large (∼100) sample of low luminosity redshift z ∼ 3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on smaller samples indicated that such sources have high [O iii]/[O ii] line ratios possibly arising from a hard ionizing spectrum that may be typical of similar sources in the reionization era. With optical spectra secured from VLT/VIMOS, we re-examine the nature of the ionizing radiation in a larger sample using the strength of the high ionization diagnostic emission lines of Ciii]λ1909, Civλ1549, Heiiλ1640, and O iii]λλ1661, 1666 Å in various stacked subsets. Our analysis confirms earlier suggestions of a correlation between the strength of Ly α and Ciii] emission and we find similar trends with broad-band UV luminosity and rest-frame UV colour. Using various diagnostic line ratios and our stellar photoionization models, we determine both the gas phase metallicity and hardness of the ionization spectrum characterized by ξion – the number of Lyman continuum photons per UV luminosity. We confirm our earlier suggestion that ξion is significantly larger for LAEs than for continuum-selected Lyman break galaxies, particularly for those LAEs with the faintest UV luminosities. We briefly discuss the implications for cosmic reionization if the metal-poor intensely star-forming systems studied here are representative examples of those at much higher redshift. [ABSTRACT FROM AUTHOR]

Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with 0.01 < z < 0.05, $\log ({\it M}_{\star }/{\it M}_{{\odot }})>9.5$ and projected axial ratio b/a > 0.32. We explore their structural properties, environments, emission lines, and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines are most likely caused by dust-star geometry, we find evidence for three different pathways through the post-starburst phase, with most events occurring in intermediate-density environments: (1) a significant disruptive event, such as a gas-rich major merger, causing a starburst and growth of a spheroidal component, followed by quenching of the star formation (70 per cent of post-starburst galaxies at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ and 60 per cent at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$ ); (2) at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ , stochastic star formation in blue-sequence galaxies, causing a weak burst and subsequent return to the blue sequence (30 per cent); (3) at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$ , cyclic evolution of quiescent galaxies which gradually move towards the high-mass end of the red sequence through weak starbursts, possibly as a result of a merger with a smaller gas-rich companion (40 per cent). Our analysis suggests that active galactic nuclei (AGNs) are 'on' for $50\hbox{ per cent}$ of the duration of the post-starburst phase, meaning that traditional samples of post-starburst galaxies with strict emission-line cuts will be at least $50\hbox{ per cent}$ incomplete due to the exclusion of narrow-line AGNs. [ABSTRACT FROM AUTHOR]

Our aim is to understand the role of the environment in the quenching of star formation of galaxies located in the infall cluster region of Abell 85 (A85). This is achieved by studying the post-starburst galaxy population as tracer of recent quenching. By measuring the equivalent width (EW) of the [O ii] and Hδ spectral lines, we classify the galaxies into three groups: passive (PAS), emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy population represents ${\sim } 4.5\hbox{ per cent}$ of the full sample. Dwarf galaxies (Mr > −18.0) account for ${\sim } 70 {\rm -} 80\hbox{ per cent}$ of PSBs, which indicates that most of the galaxies undergoing recent quenching are low-mass objects. Independently of the environment, PSB galaxies are disc-like objects with g − r colour between the blue ELs and the red PAS ones. The PSB and EL galaxies in low-density environments show similar luminosities and local galaxy densities. The dynamics and local galaxy density of the PSB population in high-density environments are shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter clustercentric radius than PAS and EL ones. The value of the EW(Hδ) is larger for those PSBs closer to the cluster centre. We propose two different physical mechanisms producing PSB galaxies depending on the environment. In low-density environments, gas-rich minor mergers or accretions could produce the PSB galaxies. For high-density environments like A85, PSBs would be produced by the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when they pass near the cluster centre. [ABSTRACT FROM AUTHOR]

Stars that exhibit a B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including the presence of Balmer lines in emission, forbidden lines and strong infrared excess due to dust. Observations of emission lines indicate illumination by an ultraviolet ionizing source, which is key to understanding the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from the Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and the correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including light absorption by the disc, pulsations, luminous blue variable type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is present not only in the disc but also above its plane. The flux and line variability is consistent with a two-component model of a circumstellar environment composed of a dense disc and an ionized envelope. Observations of B[e] supergiants show that many of these stars have nearly the same luminosity, about 1.9 × 105 L⊙, and similar effective temperatures. [ABSTRACT FROM AUTHOR]

Supernova (SN) 2016bdu is an unusual transient resembling SN 2009ip. SN 2009ip-like events are characterized by a long-lasting phase of erratic variability that ends with two luminous outbursts a few weeks apart. The second outburst is significantly more luminous (about 3mag) than the first. In the case of SN 2016bdu, the first outburst (Event A) reached an absolute magnitude Mr ≈ -15.3 mag, while the second one (Event B) occurred over one month later and reached Mr ≈ -18 mag. By inspecting archival data, a faint source at the position of SN 2016bdu is several times in the past few years. We interpret these detections as signatures of a phase of erratic variability, similar to that experienced by SN 2009ip between 2008 and mid-2012, and resembling the currently observed variability of the luminous blue variable SN 2000ch in NGC 3432. Spectroscopic monitoring of SN 2016bdu during the second peak initially shows features typical of an SN IIn. One month after the Event B maximum, the spectra develop broad Balmer lines with P Cygni profiles and broad metal features. At these late phases, the spectra resemble those of a typical Type II SN. All members of this SN 2009ip-like group are remarkably similar to the Type IIn SN 2005gl. For this object, the claim of a terminal SN explosion is supported by the disappearance of the progenitor star. While the similarity with SN 2005gl supports a genuine SN explosion scenario for SN 2009ip-like events, the unequivocal detection of nucleosynthesized elements in their nebular spectra is still missing. [ABSTRACT FROM AUTHOR]

This paper presents the results of the investigation of plasma electrolytic oxidation (PEO) of hafnium. Atoms ionized during the PEO micro-discharging were identified using optical emission spectroscopy. The spectral line shape analysis of the hydrogen Balmer line H β indicated the presence of two types of micro-discharges characterized by electron number densities of around 2.5·10 21 m − 3 and 1.3·10 22 m − 3 . Scanning electron microscopy and X-ray diffraction were employed to investigate surface morphology and phase composition of the PEO coatings obtained. The coatings were crystalline and composed of monoclinic HfO 2 . Diffuse reflectance spectroscopy has shown that HfO 2 coatings have a broad absorption band in the range from 200 nm to 400 nm. Optical band gap of HfO 2 coatings was around 5.4 eV, as estimated from absorption spectra. Photoluminescence measurements show that HfO 2 coatings have broad emission band in the visible region, with a maximum at around 480 nm. The highest photoluminescence was obtained for the excitation wavelength of 270 nm. Intensity of photoluminescence increased with PEO time and is related to an increase of oxygen vacancy defects in HfO 2 coatings formed during the process. [ABSTRACT FROM AUTHOR]

We present the results of our spectroscopic study of the dwarf nova SS Cyg, using Roche tomography to map the stellar surface and derive the system parameters. Given that this technique takes into account the inhomogeneous brightness distribution on the surface of the secondary star, our derived parameters are (in principle) the most robust yet found for this system. Furthermore, our surface maps reveal that the secondary star is highly spotted, with strongly asymmetric irradiation on the inner hemisphere. Moreover, by constructing Doppler tomograms of several Balmer emission lines, we find strong asymmetric emission from the irradiated secondary star, and an asymmetric accretion disc that exhibits spiral structures. [ABSTRACT FROM AUTHOR]

A new table of Stark–Zeeman line shapes is provided for plasma diagnostics in the framework of magnetic fusion research. Spectral profiles of D α , D β , D γ , D δ , and D ε have been calculated using computer simulations in conditions relevant to tokamak edge and divertor plasmas. After a brief presentation of the calculation method, we propose an interpolation formula and we give a routine for diagnostic applications. Analyses of experimental and synthetic spectra are performed as an illustration. [ABSTRACT FROM AUTHOR]

A new edge beam emission polarimetry diagnostic dedicated to the measurement of the magnetic field line angle has been installed on the ASDEX Upgrade tokamak. The new diagnostic relies on the motional Stark effect and is based on the simultaneous measurement of the polarization direction of the linearly polarized π (parallel to the electric field) and σ (perpendicular to the electric field) lines of the Balmer line Dα. The technical properties of the system are described. The calibration procedures are discussed and first measurements are presented. [ABSTRACT FROM AUTHOR]

Electron density profiles of versatile experiment spherical torus plasmas are measured by using a hydrogen line intensity ratio method. A fast-frame visible camera with appropriate bandpass filters is used to detect images of Balmer line intensities. The unique optical system makes it possible to take images of Hα and Hβ radiation simultaneously, with only one camera. The frame rate is 1000 fps and the spatial resolution of the system is about 0.5 cm. One-dimensional local emissivity profiles have been obtained from the toroidal line of sight with viewing dumps. An initial result for the electron density profile is presented and is in reasonable agreement with values measured by a triple Langmuir probe. [ABSTRACT FROM AUTHOR]