Hβ Line Profiles Research Articles

EIGER. V. Characterizing the Host Galaxies of Luminous Quasars at z ≳ 6

Abstract We report JWST/NIRCam measurements of quasar host galaxy emissions and supermassive black hole (SMBH) masses for six quasars at 5.9 < z < 7.1 in the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) project. We obtain deep NIRCam imaging in the F115W, F200W, and F356W bands, as well as F356W grism spectroscopy of the quasars. We use bright unsaturated stars to construct models of the point-spread functions (PSFs) and estimate the errors of these PSFs. We then measure or constrain the fluxes and morphology of the quasar host galaxies by fitting the quasar images as a point source plus an exponential disk. We successfully detect the host galaxies of three quasars, which have host-to-quasar-flux ratios of ∼1%–5%. Spectral energy distribution fitting suggests that these quasar host galaxies have stellar masses of M * ≳ 1010 M ⊙. For quasars with host galaxy nondetections, we estimate the upper limits of their stellar masses. We use the grism spectra to measure the Hβ line profile and the continuum luminosity, then estimate the SMBH masses for the quasars. Our results indicate that the positive relation between SMBH masses and host galaxy stellar masses already exists at redshift z ≳ 6. The quasars in our sample show a high BH-to-stellar-mass ratio of M BH/M * ∼ 0.15, which is about ∼2 dex higher than local relations. We find that selection effects only contribute partially to the high M BH/M * ratios of high-redshift quasars. This result hints at a possible redshift evolution of the M BH–M * relation.

Study of the Balmer Decrements for Galactic Classical Be Stars Using the Himalayan Chandra Telescope of India

In a recent study, Banerjee et al. (2021) produced an atlas of all major emission lines found in a large sample of 115 Galactic field Be stars using the 2-m Himalayan Chandra Telescope (HCT) facility located at Ladakh, India. This paper presents our further exploration of these stars to estimate the electron density in their discs. Our study using Balmer decrement values indicate that their discs are generally optically thick in nature with electron density (ne) in their circumstellar envelopes (CEs) being in excess of 1013 cm-3 for around 65% of the stars. For another 19% stars, the average ne in their discs probably range between 1012 cm-3 and 1013 cm-3. We noticed that the nature of the Hα and Hβ line profiles might not influence the observed Balmer decrement values (i.e. D34 and D54) of the sample of stars. Interestingly, we also found that around 50% of the Be stars displaying D34 greater than 2.7 are of earlier spectral types, i.e. within B0 -B3.

SPECTRAL OBSERVATIONS OF THE ALGOL - TYPE BINARY STAR δ LIBRAE

The results of spectral observations of the Algol-type binary star δ Lib are presented. The behavior of Hα and Hβ lines in the star’s spectrum during the orbital period phase is described. Based on our measurements of the radial velocities of the Hα and Hβ lines and using published data, the radial velocity curves of both components of the δ Lib system were constructed. In some phases of the orbital period, an absorption component was detected in the blue, or red, part of the Hα and Hβ line profiles. The observed Hα and Hβ absorption lines are attributed to the main component of the binary system δ Lib. It is assumed that the appearance of absorption components at these lines is associated either with suspicion of a third component in the system, or at these phases of the Hα and Hβ lines, the primary and secondary components of the δ Lib system are observed simultaneously.

Accretion/Ejection Phenomena and Emission-Line Profile (A)symmetries in Type-1 Active Galactic Nuclei

The distinct behaviors of blue- and redshifted broad emission-line shifts, emitted by ionic species with varying ionization potentials in active galactic nuclei (AGN), can be elucidated by considering the balance between radiation and gravitational forces along the quasar main sequence. Blueshifts are attributed to outflowing motions of the line-emitting gas toward the observer, and they are most pronounced in AGN with high Eddington ratios (Population A) and high luminosities. Conversely, redshifts in the broad-line wings are observed in Balmer emission lines of sources radiating at low Eddington ratios (Population B), though the origin of these redshifts remains a subject of ongoing debate. A correlation linking the redward asymmetry as measured by the centroid shift of the Hβ line profile to the black hole mass lends support to the notion that these shifts arise from gravitational and transverse redshift effects, particularly for black hole masses MBH≳108.7 M⊙.

Peculiarities of radial velocity variability of lines in the spectrum of α Cyg supergiant

ABSTRACT We use about 430 CCD spectra obtained in 1998–2001 and in 2007 to study temporal radial velocity variations of the ion, He i, and H β lines in the spectrum of the α Cyg. We found that these variations are caused by pulsation-type motions. In case of the ion and He i lines, fluctuations occur in the fundamental radial mode with the period of about 12.5 ± 1.0 d and the amplitude of 5.0 ± 0.5 km s−1. The oscillation lasts about ∼34 ± 1 d. In the case of the H β line the radial velocity variability was studied separately for the blue and red halves of the line profile. Such a methodical approach allowed to discover three characteristic cases of radial velocity variability for the blue and red halves of the H β line profile. In 1999 and 2001, the period P and amplitude A variability parameters are the same for the blue and red halves, and hence for the line bisector too. In 1998, P and A are the same for the blue and red halves of the profile, however, there is a phase shift between the fluctuations of their radial velocity by 0.6P. In 2000, P and A are different for the two halves of the line profile. Relative to the center of the star’s mass, the average expansion rate for the atmospheric layers, where the H β line is formed, is about −10.0 km s−1. It varies over time with a semi-amplitude of around ±3.3 km s−1.

Long-term optical spectral monitoring of a changing-look active galactic nucleus NGC 3516

Context.We analyze the broad Hβline profile variability of a “changing look” active galactic nucleus (CL-AGN) NGC 3516 over an extensive period of 25 years (from 1996 to 2021). The observed change in the broad line profile may indicate a change in the geometry of the broad line region (BLR). The main objective is to follow and understand the change in the BLR over a long period as well as its connection to the CL mechanism.Aims.Using spectral line profiles, we aim to explore changes in the kinematics and dimensions of the BLR in NGC 3516. We consider two possible scenarios: the changes in the broad-line emission are either caused by a decrease of ionisation continuum emission or by the BLR obscuration by outer dusty regions. With this investigation, we aim to clarify the CL mechanism of this AGN.Methods.We analyzed the spectral band around the Hβline as well as the broad Hβline parameters and how they change over time. We modelled the broad-line profiles, assuming that there is an emission from the accretion disc superposed with emission from a surrounding region that is outside the disc.Results.We find that in the type 1 activity phase occurring when the strong broad emission lines are observed, the BLR is very complex. There is a clear disc-like BLR that contributes to the broad line wings and an additional intermediate line region (ILR) that contributes to the line core. In the high-activity phase, the ILR emission is close to the center of the line, although in some cases, it is slightly shifted to the red. In the low-activity phase (i.e. type 2 phase), the ILR component has a significant shift to the blue, indicating an outflow.Conclusions.We propose that the changing-look mechanism in NGC 3516 is rather connected with the intrinsic effects than with an outer obscuring region. It may still be possible that the dust plays an important role in the low-activity phase when it is coming from within the BLR, leading to a dusty BLR. In this way, it would cause a decrease in the ionisation and recombination rates.

Hidden Spectra Treasures in the Foster Archive: A Pilot Study of the Be Stars α Eri, α Col, ω Car and η Cen

We present the archive of spectroscopic photographic plates of the Universidad Católica historic observatory Manuel Foster. The archive includes more than 4800 plates covering the period of time from 1928 to 1991. The spectra present in the archive are mostly those of bright variable or binary stars observed at different epochs. We developed a method of digitalization and data processing for the plates and verified it through the analysis of a selected sample of spectra. As an example of the potential relevance of this Foster archive we studied the variation of helium, Hβ and Hγ spectral lines over time (1980−1991), complementing with high resolution spectroscopic data from the “Be Star Observation Survey” (2012−2015), of four Be stars mainly, α Eri, α Col, ω Car and η Cen. The spectra of these stars show evidence of a circumstellar gas disk present in both periods of time. From the spectroscopic analysis, we found these stars are variable in helium and this variability presents an opposite behavior with the variability observed in the EW of the Hβ line profile. This archive represents a unique source of data from past that is available for the use of the community.

Beyond the dips of V807 Tau, a spectropolarimetric study of a dipper’s magnetosphere

Context. The so-called dippers are pre-main-sequence objects that accrete material from their circumstellar disks through the stellar magnetosphere. Their unique type of variability allows us to probe the magnetic star-disk interaction processes in young stellar objects. Aims. We aim to characterize the magnetospheric accretion process in the young stellar object V807 Tau, one of the most stable dippers revealed by K2 in the Taurus star forming region. Methods. We performed photometric and spectropolarimetric follow-up observations of this system with CFHT/ESPaDOnS in order to investigate the variability of the system over several rotational periods. Results. We derive a 4.38 day period from the K2 dipper light curve. This period is also seen in the radial velocity variations, which we ascribe to spot modulation. The slightly redshifted narrow component of the He I 5876 Å line as well as the high velocity red wing of the Hβ and Hγ emission line profiles also vary in intensity with the same periodicity. The former traces the accretion shock at the stellar surface, and the latter is a signature of an accretion funnel flow crossing the line of sight. We derive a surface brightness map and the topology of the surface magnetic field from the modeling of Stokes I and V profiles, respectively, for photospheric lines and for the He I emission line. The latter reveals a bright spot at the stellar surface, located at a latitude of 60°, and a maximum field strength of ∼2 kG at this location. The topology of the magnetic field at the stellar surface is dominated by a dipolar component inclined by about 40° onto the spin axis. Variable blueshifted absorption components seen in the Balmer line profiles suggest episodic outflows. Despite of its clear and stable dipper behavior, we derive a relatively low inclination of 40° to 50° for this system, which calls question the origin of the dips. The low inclination we infer is also consistent with the absence of deep inverse P Cygni components in the line profiles. Conclusions. We conclude that magnetospheric accretion is ongoing in V807 Tau, taking place through non-axisymmetric accretion funnel flows controlled by a strong, tilted, and mainly dipolar magnetic topology. Whether an inner disk warp resulting from this process can account for the dipper character of this source remains to be seen, given the low inclination of the system.

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Context. Several observational and theoretical results indicate that the atmospheric temperature of the ultra-hot Jupiter KELT-9b in the main line formation region is a few thousand degrees higher than predicted by self-consistent models. Aims. Our aim was to test whether non-local thermodynamic equilibrium (NLTE) effects are responsible for the presumably higher temperature. Methods. We employed the Cloudy NLTE radiative transfer code to self-consistently compute the upper atmospheric temperature-pressure (TP) profile of KELT-9b, assuming solar metallicity and accounting for Roche potential. In the lower atmosphere, we used an updated version of the HELIOS radiative-convective equilibrium code to constrain the Cloudy model. Results. The Cloudy NLTE TP profile is ≈2000 K hotter than that obtained with previous models assuming LTE. In particular, in the 1–10−7 bar range the temperature increases from ≈4000 to ≈8500 K, remaining roughly constant at lower pressures. We find that the high temperature in the upper atmosphere of KELT-9b is driven principally by NLTE effects modifying the Fe and Mg level populations, which strongly influence the atmospheric thermal balance. We employed Cloudy to compute LTE and NLTE synthetic transmission spectra on the basis of the TP profiles computed in LTE and NLTE, respectively, finding that the NLTE model generally produces stronger absorption lines, particularly in the ultraviolet, than the LTE model (up to 30%). We compared the NLTE synthetic transmission spectrum with the observed Hα and Hβ line profiles obtaining an excellent match, thus supporting our results. Conclusions. The NLTE synthetic transmission spectrum can be used to guide future observations aiming at detecting features in the KELT-9b transmission spectrum. Metals, such as Mg and Fe, and NLTE effects shape the upper atmospheric temperature structure of KELT-9b, and thus affect the mass-loss rates derived from it. Finally, our results call for checking whether this is the case also for cooler planets.

SUPER

Aims.The SINFONI survey for Unveiling the Physics and Effect of Radiative feedback (SUPER) was designed to conduct a blind search for AGN-driven outflows on X-ray-selected AGNs at redshiftz ∼ 2 with high (∼2 kpc) spatial resolution, and to correlate them with the properties of their host galaxy and central black hole. The main aims of this paper are: (a) to derive reliable estimates for the masses of the black holes and accretion rates for the Type-1 AGNs in this survey; and (b) to characterise the properties of the AGN-driven winds in the broad line region (BLR).Methods.We analysed rest-frame optical and UV spectra of 21 Type-1 AGNs. We used Hα, Hβ, and MgII line profiles to estimate the masses of the black holes. We used the blueshift of the CIV line profile to trace the presence of winds in the BLR.Results.We find that the Hαand Hβline widths are strongly correlated, as is the line continuum luminosity at 5100 Å with Hαline luminosity, resulting in a well-defined correlation between black hole masses estimated from Hαand Hβ. Using these lines, we estimate that the black hole masses for our objects are in the range Log (MBH/M⊙) = 8.4–10.8 and are accreting atλEdd= 0.04–1.3. Furthermore, we confirm the well-known finding that the CIV line width does not correlate with the Balmer lines and the peak of the line profile is blueshifted with respect to the [OIII]-based systemic redshift. These findings support the idea that the CIV line is tracing outflowing gas in the BLR for which we estimated velocities up to ∼4700 km s−1. We confirm the strong dependence of the BLR wind velocity on the UV-to-X-ray continuum slope, the bolometric luminosity, and Eddington ratio. We infer BLR mass outflow rates in the range 0.005–3M⊙yr−1, revealing a correlation with the bolometric luminosity consistent with that observed for ionised winds in the narrow line region (NLR), and X-ray winds detected in local AGNs, and kinetic power ∼10−7 − 10−4 × LBol. The coupling efficiencies predicted by AGN-feedback models are much higher than the values reported for the BLR winds in the SUPER sample; although it should be noted that only a fraction of the energy injected by the AGN into the surrounding medium is expected to become kinetic power in the outflow. Finally, we find an anti-correlation between the equivalent width of the [OIII] line and the CIV velocity shift, and a positive correlation between this latter parameter and [OIII] outflow velocity. These findings, for the first time in an unbiased sample of AGNs atz ∼ 2, support a scenario where BLR winds are connected to galaxy-scale detected outflows, and are therefore capable of affecting the gas in the NLR located at kiloparsec scale distances.

Evidence for Two Distinct Broad-line Regions from Reverberation Mapping of PG 0026+129

Abstract We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2 m telescope from 2017 July to 2020 February. Significant variations in the fluxes of the continuum and broad emission lines, including Hβ and He ii, were observed in the first and third years, and clear time lags between them are measured. The broad Hβ line profile consists of two Gaussian components: an intermediate-width H with an FWHM of 1964 ± 18 and another very broad H with an FWHM of 7570 ± 83 . H has long time lags of ∼40–60 days in the rest frame, while H shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of ∼30–50 days at the core of the broad Hβ line and roughly zero lags at the wings. H has a redshift of ∼400 , which seems to be stable for nearly 30 yr by comparing with archived spectra, and may originate from an infall. The rms spectrum of H shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. Both the double-peaked profile and the near-zero lag suggest that H comes from a region associated with the part of the accretion disk that emits the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag measured for the total Hβ line, and a virial factor of 1.5, we obtain a virial mass of for the central black hole in this quasar.

LLAMA: TheMBH–σ⋆relation of the most luminous local AGNs

Context.TheMBH–σ⋆relation is considered a result of coevolution between the host galaxies and their supermassive black holes. For elliptical bulge hosting inactive galaxies, this relation is well established, but there is still discussion concerning whether active galaxies follow the same relation.Aims.In this paper, we estimate black hole masses for a sample of 19 local luminous active galactic nuclei (AGNs; LLAMA) to test their location on theMBH–σ⋆relation. In addition, we test how robustly we can determine the stellar velocity dispersion in the presence of an AGN continuum and AGN emission lines, and as a function of signal-to-noise ratio.Methods.Supermassive black hole masses (MBH) were derived from the broad-line-based relations for Hα, Hβ, and Paβemission line profiles for Type 1 AGNs. We compared the bulge stellar velocity dispersion (σ⋆) as determined from the Ca II triplet (CaT) with the dispersion measured from the near-infrared CO (2-0) absorption features for each AGN and find them to be consistent with each other. We applied an extinction correction to the observed broad-line fluxes and we corrected the stellar velocity dispersion by an average rotation contribution as determined from spatially resolved stellar kinematic maps.Results.The Hα-based black hole masses of our sample of AGNs were estimated in the range 6.34 ≤ logMBH ≤ 7.75M⊙and theσ⋆CaTestimates range between 73 ≤ σ⋆CaT ≤ 227 km s−1. From the so-constructedMBH − σ⋆relation for our Type 1 AGNs, we estimate the black hole masses for the Type 2 AGNs and the inactive galaxies in our sample.Conclusions.We find that our sample of local luminous AGNs is consistent with theMBH–σ⋆relation of lower luminosity AGNs and inactive galaxies, after correcting for dust extinction and the rotational contribution to the stellar velocity dispersion.

Black hole mass estimates in quasars

Context. The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the structure and dynamics of the quasar broad line region (BLR), including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. Aims. We carried out an analysis of the C IVλ1549 and Hβ line profiles of 28 Hamburg-ESO high-luminosity quasars and of 48 low-z, low-luminosity sources in order to test whether the width of the high-ionization line C IVλ1549 could be correlated with Hβ and be used as a virial broadening estimator. Methods. We analyze intermediate- to high-S/N, moderate-resolution optical and near-infrared (NIR) spectra covering the redshifted C IVλ1549 and Hβ over a broad range of luminosity log L ∼ 44 − 48.5 [erg s−1] and redshift (0 − 3), following an approach based on the quasar main sequence. Results. The present analysis indicates that the line width of C IVλ1549 is not immediately offering a virial broadening estimator equivalent to Hβ. At the same time a virialized part of the BLR appears to be preserved even at the highest luminosities. We suggest a correction to FWHM(C IVλ1549) for Eddington ratio (using the C IVλ1549 blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity. Conclusions. Great care should be used in estimating high-L black hole masses MBH from C IVλ1549 line width. However, once a corrected FWHM C IVλ1549 is used, a C IVλ1549-based scaling law can yield unbiased MBH values with respect to the ones based on Hβ with sample standard deviation ≈0.3 dex.

Formation of Hydrogen Emission Lines in the Magnetospheres of Young Stars

The formation of hydrogen emission lines in the magnetospheres of young stars is considered. The magnetosphere is assumed to be formed by a dipolar magnetic field whose axis is aligned with the stellar rotation axis. The radiative transfer in spectral lines is considered in the Sobolev approximation by taking into account the nonlocal radiative coupling. The gas density and temperature distributions in the magnetosphere are taken to be the same as those in Hartmann et al. (1994). The results of our calculations of the Hα and Hβ line intensities and profiles are presented for the case of a slowly rotating star. We separately consider the magnetospheric models in which the infalling gas is heated by radiation from an accretion spot on the stellar surface and the case where the axis of the magnetosphere is tilted with respect to the stellar rotation axis. Rotational modulation of the spectral line profiles with the stellar rotation period is observed in the latter case.

Characterization of novel pin-hole based plasma source for generation of discharge in liquids supplied by DC non-pulsing voltage

A recently presented novel plasma source generating discharge in liquids based on the pin-hole discharge configuration is characterized in detail. The system is supplied by DC non-pulsing high voltage of both polarities in NaCl water solutions at a conductivity range of 100–15 000 μS/cm. The discharge itself shows self-pulsing operation. The discharge ignition is observed in micro bubbles by transient discharge followed by a glow discharge in positive polarity at lower conductivities propagating inside the bubbles. At high conductivities, the glow regime is particularly replaced by a more energetic sequence of transient discharges followed by a shorter glow mode operation. The transient regime probability and its intensity are higher in the negative discharge polarity. The transient discharge produces acoustic waves and shock waves, which are observed at the moment of the bubble cavitation. The average gas temperature of 700–1500 K was calculated from the lowest OH (A-X) 0-0 band transitions. The average electron concentrations of 1020–1023 m−3 were calculated from Hα and Hβ line profiles. Finally, the production of a chemically active species is determined by hydrogen peroxide energy yields related to the energy consumption of the whole interelectrode system. All these quantities are dependent on the solution conductivity, the discharge polarity, and the applied power.

Study of the non-stationarity of the atmosphere of κ Cas. Ii. Variability of the Hγ, Hβ, and Hα wind-line profiles

We study the variability of the Hγ, Hβ, and Hα line profiles in the spectrum of the supergiant κ Cas. The variability pattern proved to be the same for all the lines considered: their profiles are superimposed by blueshifted, central, and redshifted emission. For Hγ the positions of the emissions coincide with the positions of the corresponding emissions for He I λλ 5876, 6678 A lines, and are equal to about −135 ± 30.0 km s−1, −20 ± 20 kms−1, and 135 ± 30.0 kms−1, respectively, whereas the three emissions in the Hβ profiles are fixed at about −170.0 ± 70.0 kms−1, 20 ± 30 kms−1, and 170.0 ± 70.0 km s−1, respectively. The positions of the blueshifted and central emissions for Hα are the same as for Hβ, with additional blueshifted emission at −135.0 ± 30.0 kms−1, whereas no traces of emission can be seen in the red wing of the line. These emissions show up more conspicuously in wind lines, however, their traces can be seen in all photospheric lines. When passing from wind lines to photospheric lines the intensity of superimposed emission components decreases and the same is true for the absolute values of their positions in line wings expressed in terms of radial velocities. The V/R variations of the lines studied found in the spectrum of κ Cas and the variability of the Hα emission indicate that the star is a supergiant showing Be phenomenon.

Electron density and temperature diagnostics in laser-induced hydrogen plasma

Laser-induced optical breakdown is achieved by using Q-switched, Nd:YAG radiation focused into ultra-high-purity (UHP) hydrogen gas at a pressure of 1.08 ± 0.03 × 105 Pa inside a cell. The plasma emission spectra are dispersed by a Czerny-Turner type spectrometer and detected with an intensified charge-coupled device (ICCD). Stark-broadened hydrogen Balmer series Hα and Hβ line profiles are used as a spectroscopic tool for the determination of electron density and excitation temperature. Spatial variation of electron density and temperature at 0.40 µs are extracted from the recorded intensities of Hα and Hβ lines. Temporal variations of electron density and excitation temperature are also presented for the time delay range of 0.15 µs to 1.4 µs.

A LOW-MASS BLACK HOLE IN THE NEARBY SEYFERT GALAXY UGC 06728

ABSTRACT We present the results of a recent reverberation mapping campaign for UGC 06728, a nearby low-luminosity Seyfert 1 in a late-type galaxy. Nightly monitoring in the spring of 2015 allowed us to determine an Hβ time delay of days. Combined with the width of the variable Hβ line profile, we determine a black hole mass of . We also constrain the bulge stellar velocity dispersion from higher-resolution long-slit spectroscopy along the galaxy minor axis and find km s−1. The measurements presented here are in good agreement with both the relationship and the relationship for active galactic nuclei. Combined with a previously published spin measurement, our mass determination for UGC 06728 makes it the lowest-mass black hole that has been fully characterized, and thus an important object to help anchor the low-mass end of black hole evolutionary models.

Experimental and theoretical study of atmospheric-pressure argon microplasma jets

Surface-wave discharges in argon at atmospheric pressure were experimentally studied by optical emission spectroscopy (OES) and mass spectrometry (MS). OES was employed to determine the rotational temperature using the ultraviolet OH band, Q1 branch and found to be between 450 and 970 K. The electron density (5 × 1013 cm−3 ≤ ne ≤ 7 × 1014 cm−3) was estimated using the Hβ line profile, and produced by dissociation of the water present as an impurity in the Ar gas. The electron temperature (0.63 eV ≤ Te ≤ 1.3 eV) was estimated using a collisional–radiative (CR) model that takes the input measured intensities of four emission lines originating from 2p states including 2p2, 2p4, 2p6, and 2p10. The density of the metastable state Ar(1s5) (2.0 × 1011 cm−3 ≤ Ar(1s5) ≤ 4.2 × 1012 cm−3) was estimated by means of OES using the self-absorbing method. Positive and negative ions were probed along the plasma column using MS. A theoretical model based on the solution of the homogeneous electron Boltzmann equation, considering inelastic and superelastic collisions with the Ar(1s) states and electron–electron collisions, coupled with a system of rate balance equations describing the creation and destruction of the most important heavy particles, is proposed. The experimental results are compared with theoretical ones obtained from a self-consistent model of these discharges, providing physical insight into the basic mechanisms and phenomena ruling the discharges.

Spectroscopic study of plasma during electrolytic oxidation of magnesium-aluminium alloys

Plasma during Electrolytic Oxidation (PEO) of magnesium-aluminium alloys is studied in this work by means of Optical Emission Spectroscopy (OES). Spectral line shapes of the Hβ, Al II 704.21 nm and Mg II 448.11 nm line are analyzed to measure plasma electron number density Ne. From the Hβ line profile, two PEO processes characterized by relatively low electron number densities Ne ≈ 1015 cm−3 and Ne ≈ 2 × 1016 cm−3 were discovered while the shape and shift of Al II and Mg II lines revealed the third process characterized by large electron density Ne = (1-2) × 1017 cm−3. Low Ne processes, related with breakdown in gas bubbles and on oxide surface, are not influenced by anode material or electrolyte composition. The ejection of evaporated anode material through oxide layer is designated here as third PEO process.Using the Boltzmann plot technique, electron temperature of 4000 K and 33000 K is determined from relative intensities of Mg I and O II lines, respectively. Several difficulties in the analysis of spectral line shapes are met during this study and the ways to overcome some of the obstacles are demonstrated.