Line Intensity Ratios Research Articles

Mapping the high ionization rate of the GC starburst Sgr B2 through low HCO+ /N2H+ J=1-0 intensity ratios

We still do not understand which mechanisms dominate the heating and ionization of the extended molecular gas in galactic nuclei. The starburst Sgr B2, in the Galactic Center (GC), is an excellent template to spatially resolve the high-mass star-forming cores from the extended cloud environment, and to study the properties of the warm neutral gas in conditions likely prevalent in star-forming galaxies. We mapped ~1000 pc2 of Sgr B2 complex, using the IRAM 30m telescope, in the N2H+, HCO+ J=1-0 and SiO J=2-1 line emission. The extended nature of the N2H+ J=1-0 emission is remarkable. Compared to molecular clouds in the disk of the galaxy, the N2H+ J=1-0 emission is not confined to cold and dense cores and filaments. This can be explained by the high ionization rate (ζ ≳10−15 s−1), leading to overabundant H+3, He+, and N2H+. The enhanced ionization rate is likely responsible of the much lower line intensity ratio RI =HCO+/N2H+ J=1-0 observed in Sgr B2 (RI ≈ 2 ± 2), Arp 220 (RI ≈ 2), and NGC 253 (RI ≈ 5), compared to disk clouds such as Orion B (RI ≈ 24) and starburst galaxies such as M82 (RI ≈ 21).

Generation of Atmospheric Pressure Dielectric Barrier Discharge (DBD) Using Water Electrode

In this experiment, an atmospheric pressure dielectric barrier discharge (DBD) generated with a water electrode is investigated by means of optical measurements and imaging. The discharge was generated using a high voltage (0-20kV) power supply operating at 10-30 kHz with water as one of the electrode and borosilicate glass as a dielectric barrier of 2.5mm thickness. This paper reports the generation and characterization of atmospheric pressure plasma in nitrogen environment and its application in the surface modification of polyethylene terephthalate (PET). The generated plasma has been characterized by image analysis and optical emission spectroscopy. Our results showed that the distribution of micro-discharges depends significantly on the inter electrode gap and applied voltage. In order to characterize the discharge, electron temperature has been determined by using line intensity ratio method. The results showed that Te depends on applied voltage and pressure inside the chamber. The values of Te were found to be 1.40 eV and 0.95 eV applied at 1kV and 10kV voltage using 1% concentration. The discharge was produced at various conditions for the study of effectiveness of treatment on the surface property of Polyethylene terephthalate (PET). After the treatment of the sample in different treatment time: 10s, 20s, 40s, and 60s, the hydrophobic properties of sample changed to the hydrophilic. To investigate the effect of plasma treatment on Polyethylene terephthalate (PET) polymer contact angle was measured by using goniometer with water as a testing liquid. The surface properties of the untreated and plasma treated PET samples were characterized by contact angle measurement, and surface energy analysis. Before treatment the contact angle for untreated sample was 77.1° and after treatment its contact angle becomes 38.7° , 35.04° , 33.6° and 31.6° respectively.

Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound NiTe2O5

A $^{125}$Te nuclear magnetic resonance (NMR) study was carried out in the paramagnetic state of the recently discovered quasi-one-dimensional spin-1 chain compound NiTe$_2$O$_5$. We observed that the $^{125}$Te NMR spectrum splits into two in a magnetic field applied along the $c$ axis. Based on the strong temperature variation of the relative intensity ratio of the split lines, we infer that the line splitting arises from the two sublattice susceptibilities induced in opposite directions along the chains. In great support of this interpretation, a quantitative analysis of the spin-lattice relaxation rate $T_1^{-1}$ and the Knight shift data unravels dominant transverse spin fluctuations. We conclude that Ising-like uniaxial spin correlations persist up to surprisingly high temperatures compared to the exchange energy scales. Spin-charge coupling mechanism via a self-doping effect may be important.

KAPPA: A Package for the Synthesis of Optically Thin Spectra for the Non-Maxwellian κ-distributions. II. Major Update to Compatibility with CHIANTI Version 10

Abstract KAPPA is a database and software for the calculation of the optically thin spectra for the non-Maxwellian κ-distributions that were recently diagnosed in the plasma of solar coronal loops, flares, as well as in the transition region. KAPPA is based on the widely used CHIANTI database and reproduces many of its capabilities for κ-distributions. Here we perform a major update of the KAPPA database, including a near-complete recalculation of the ionization, recombination, excitation, and deexcitation rates for all ions in the database, as well as an implementation of the two-ion model for calculations of relative-level populations (and intensities) if these are modified by ionization and recombination from or to excited levels. As an example of KAPPA usage, we explore novel diagnostics of κ, and show that O iii lines near 500 and 700 Å provide a strong sensitivity to κ, with some line intensity ratios changing by a factor of up to 2–4 compared to Maxwellian. This is much larger than previously employed diagnostics of κ.

A Spectroscopic Study of Supernova Remnants with the Infrared Space Observatory*

Abstract We present far-infrared (FIR) spectroscopy of supernova remnants (SNRs) based on the archival data of the Infrared Space Observatory taken with the Long Wavelength Spectrometer (LWS). Our sample includes previously unpublished profiles of line and continuum spectra for 20 SNRs in the Galaxy and Magellanic Clouds. In several SNRs including G21.5–0.9, G29.7–0.3, the Crab Nebula, and G320.4–1.2, we find evidence for broad [O i], [O iii], [N ii], and [C ii] lines with velocity dispersions up to a few 103 km s−1, indicating that they are associated with high-velocity SN ejecta. Our detection of Doppler-broadened atomic emission lines and a bright FIR continuum hints at the presence of newly formed dust in SN ejecta. For G320.4–1.2, we present the first estimate of an ejecta-dust mass of 0.1–0.2 M ⊙, which spatially coincides with the broad-line emission, by applying a blackbody model fit with components of the SNR and background emission. Our sample includes raster maps of 63 μm, 145 μm [O i], and 158 μm [C ii] lines toward SNRs Kes 79, CTB 109, and IC 443. Based on these line intensities, we suggest interacting shock types in these SNRs. Finally, we compare our LWS spectra of our sample SNRs with the spectra of several H ii regions, and discuss their FIR line intensity ratios and continuum properties. Follow-up observations with modern instruments (e.g., JWST and SOFIA) with higher spatial and spectral resolution are encouraged for an extensive study of the SN ejecta and the SN dust.

Evaluation of gases’ molecular abundance ratio by fiber-optic laser-induced breakdown spectroscopy with a metal-assisted method

A metal-assisted method is proposed for the evaluation of gases’ molecular abundance ratio in fiber-optic laser-induced breakdown spectroscopy (FO-LIBS). This method can reduce the laser ablation energy and make gas composition identification possible. The principle comes from the collision between the detected gases and the plasma produced by the laser ablation of the metal substrate. The interparticle collision in the plasma plume leads to gas molecules dissociating and sparking, which can be used to determine the gas composition. The quantitative relationship between spectral line intensity and molecular abundance ratio was developed over a large molecular abundance ratio range. The influence of laser ablation energy and substrate material on gas quantitative calibration measurement is also analyzed. The proposed metal-assisted method makes the measurement of gases’ molecular abundance ratios possible with an FO-LIBS system.

Effect of the target positions on the rapid identification of aluminum alloys by using filament-induced breakdown spectroscopy combined with machine learning

Filament-induced breakdown spectroscopy (FIBS) combined with machine learning algorithms was used to identify five aluminum alloys. To study the effect of the distance between focusing lens and target surface on the identification accuracy of aluminum alloys, principal component analysis (PCA) combined with support vector machine (SVM) and K-nearest neighbor (KNN) was used. The intensity and intensity ratio of fifteen lines of six elements (Fe, Si, Mg, Cu, Zn, and Mn) in the FIBS spectrum were selected. The distances between the focusing lens and the target surface in the pre-filament, filament, and post-filament were 958 mm, 976 mm, and 1000 mm, respectively. The source data set was fifteen spectral line intensity ratios, and the cumulative interpretation rates of PC1, PC2, and PC3 were 97.22%, 98.17%, and 95.31%, respectively. The first three PCs obtained by PCA were the input variables of SVM and KNN. The identification accuracy of the different positions of focusing lens and target surface was obtained, and the identification accuracy of SVM and KNN in the filament was 100% and 90%, respectively. The source data set of the filament was obtained by PCA for the first three PCs, which were randomly selected as the training set and test set of SVM and KNN in 3:2. The identification accuracy of SVM and KNN was 97.5% and 92.5%, respectively. The research results can provide a reference for the identification of aluminum alloys by FIBS.

Electron Density Dependence of Extreme Ultraviolet Line Intensity Ratios in Ar XIV

Abstract We report the electron density dependence of extreme ultraviolet line intensity ratios in Ar xiv studied using a well-defined electron beam ion trap plasma. The purpose of this study is to examine the potential of the Ar xiv lines in diagnosing the electron density of solar corona active regions with a temperature higher than 3 MK. The experimentally obtained dependence is in good agreement with collisional-radiative model calculations, which ensures the usability of the Ar xiv lines.

A study on the relationship between spectral characterization and composition of plasma in laser additive manufacturing of gradient materials

PurposeThe purpose of this paper is to predict and control the composition during laser additive manufacturing, since composition control is important for parts manufactured by laser additive manufacturing. Aluminum and steel functionally graded material (FGM) were manufactured by laser metal deposition, and the composition was analyzed by means of spectral analysis simultaneously.Design/methodology/approachThe laser metal deposition process was carried out on a 5 mm thick 316L plate. Spectral line intensity ratio and plasma temperature were chosen as two main spectroscopic diagnosis parameters to predict the compositional variation. Single-trace single-layer experiments and single-trace multi-layer experiments were done, respectively, to test the feasibility of the spectral diagnosis method.FindingsExperiment results showed that with the composition of metal powder changing from steel to aluminum, the spectral intensity ratio of the characteristic spectral line is proportional to the elemental content in the plasma. When the composition of deposition layers changed, the characteristic spectrum line intensity ratio changed obviously. And the linear chemical composition analysis results confirmed the gradient composition variation of the additive manufacturing parts. The results verified the feasibility of composition analysis based on spectral information in the laser additive manufacturing process.Originality/valueThe composition content of aluminum and steel FGM was diagnosed by spectral information during laser metal deposition, and the relationship between spectral intensity and composition was established.

Forward Modeling of Solar Coronal Magnetic-field Measurements Based on a Magnetic-field-induced Transition in Fe x

Abstract It was recently proposed that the intensity ratios of several extreme ultraviolet spectral lines from Fe x ions can be used to measure the solar coronal magnetic field based on magnetic-field-induced transition (MIT) theory. To verify the suitability of this method, we performed forward modeling with a three-dimensional radiation magnetohydrodynamic model of a solar active region. Intensities of several spectral lines from Fe x were synthesized from the model. Based on MIT theory, the intensity ratios of the MIT line Fe x 257 Å to several other Fe x lines were used to derive magnetic-field strengths, which were then compared with the field strengths in the model. We also developed a new method to simultaneously estimate the coronal density and temperature from the Fe x 174/175 and 184/345 Å line ratios. Using these estimates, we demonstrated that the MIT technique can provide reasonably accurate measurements of the coronal magnetic field in both on-disk and off-limb solar observations. Our investigation suggests that a spectrometer that can simultaneously observe the Fe x 174, 175, 184, 257, and 345 Å lines and allow an accurate radiometric calibration for these lines is highly desired to achieve reliable measurements of the coronal magnetic field. We have also evaluated the impact of the uncertainty in the Fe x 3p4 3d 4D5/2 and 4D7/2 energy difference on the magnetic-field measurements.

Charge exchange recombination spectroscopy of W (q = 61–66) for application to ITER neutral hydrogen beam diagnostics

In this paper, we present a detailed theoretical analysis of charge exchange recombination spectroscopy based on interactions of the planned ITER neutral beams (diagnostic beam of 100 keV u−1 and heating beam of ≈1 MeV u−1) with highly-charged ions of tungsten. The results of the present spectral synthesis are based on the new set of nl-resolved charge exchange (CX) cross sections for recombination of the W ions (q = 61–66) with atomic hydrogen calculated using the classical trajectory Monte Carlo method. A large-scale collisional-radiative model describing the population kinetics of the high-n atomic states of Si-like through O-like W ions has been developed using the NOMAD code for typical conditions of the ITER core plasma, and the resulting spectra have been generated for wavelengths in the x-ray to visible range (0.1–1000 nm). A detailed analysis of the plasma emission predicts a significant effect of CX recombination on the W line intensity ratios that can be used for more advanced diagnostics of the ITER plasma.

A spectral library for laser-induced fluorescence analysis as a tool for rare earth element identification

Abstract. With the recurring interest in rare earth elements (REEs), laser-induced fluorescence (LiF) may provide a powerful tool for their rapid and accurate identification at different stages along their value chain. Applications to natural materials such as minerals and rocks could complement the spectroscopy-based toolkit for innovative, non-invasive exploration technologies. However, the diagnostic assignment of detected emission lines to individual REEs remains challenging because of the complex composition of natural rocks in which they can be found. The resulting mixed spectra and the large amount of data generated demand automated approaches of data evaluation, especially in mapping applications such as drill core scanning. LiF reference data provide the solution for robust REE identification, yet they usually remain in the form of tables of published emission lines. We show that a complete reference spectra library could open manifold options for innovative automated analysis. We present a library of high-resolution LiF reference spectra using the Smithsonian rare earth phosphate standards for electron microprobe analysis. We employ three standard laser wavelengths (325, 442, 532 nm) to record representative spectra in the UV-visible to near-infrared spectral range (340–1080 nm). Excitation at all three laser wavelengths yielded characteristic spectra with distinct REE-related emission lines for EuPO4, TbPO4, DyPO4 and YbPO4. In the other samples, the high-energy excitation at 325 nm caused unspecific, broad-band defect emissions. Here, lower-energy laser excitation is shown to be successful for suppressing non-REE-related emission. At 442 nm excitation, REE reference spectra depict the diagnostic emission lines of PrPO4, SmPO4 and ErPO4. For NdPO4 and HoPO4 the most efficient excitation was achieved with 532 nm. Our results emphasise the possibility of selective REE excitation by changing the excitation wavelength according to the suitable conditions for individual REEs. Our reference spectra provide a database for the transparent and reproducible evaluation of REE-bearing rocks. The LiF spectral library is available at zenodo.org and the registered DOI https://doi.org/10.5281/zenodo.4054606 (Fuchs et al., 2020). Primarily addressing the raw material exploration sector, it aids particularly the development of advanced data processing routines for LiF analysis but can also support further research on the REE luminescence in natural rocks or artificial compounds. It gives access to traceable data for the comparison of emission line positions, emission line intensity ratios and splitting into emission line sub-levels or can be used as reference or training data for automated approaches of component assignment.

Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.

Interpreting automatic AGN classifiers with saliency maps

Classification of the optical spectra of active galactic nuclei (AGN) into different types is currently based on features such as line widths and intensity ratios. Although well founded on AGN physics, this approach involves some degree of human oversight and cannot scale to large datasets. Machine learning (ML) tackles this classification problem in a fast and reproducible way, but is often (and not without reason) perceived as a black box. However, ML interpretability and are active research areas in computer science that are providing us with tools to mitigate this issue. We apply ML interpretability tools to a classifier trained to predict AGN types from spectra. Our goal is to demonstrate the use of such tools in this context, obtaining for the first time insight into an otherwise black box AGN classifier. In particular, we want to understand which parts of each spectrum most affect the predictions of our classifier, checking that the results make sense in the light of our theoretical expectations. We trained a support-vector machine on 3346 high-quality, low-redshift AGN spectra from SDSS DR15. We considered either two-class classification (type 1 versus 2) or multiclass (type 1 versus 2 versus intermediate-type). The spectra were previously and independently hand-labeled and divided into types 1 and 2, and intermediate-type (i.e., sources in which the Balmer line profile consists of a sharp narrow component superimposed on a broad component). We performed a train-validation-test split, tuning hyperparameters and independently measuring performance via a variety of metrics. On a selection of test-set spectra, we computed the gradient of the predicted class probability at a given spectrum. Regions of the spectrum were then color-coded based on the direction and the amount by which they influence the predicted class, effectively building a saliency map. We also visualized the high-dimensional space of AGN spectra using t-distributed stochastic neighbor embedding (t-SNE), showing where the spectra for which we computed a saliency map are located. Our best classifier reaches an F-score of 0.942 on our test set (with 0.948 precision and 0.936 recall). We computed saliency maps on all misclassified spectra in the test set and on a sample of randomly selected spectra. Regions that affect the predicted AGN type often coincide with physically relevant features, such as spectral lines. t-SNE visualization shows good separability of type 1 and type 2 spectra. Intermediate-type spectra either lie in-between, as expected, or appear mixed with type 2 spectra. Misclassified spectra are typically found among the latter. Some clustering structure is apparent among type 2 and intermediate-type spectra, though this may be an artifact. Saliency maps show why a given AGN type was predicted by our classifier resulting in a physical interpretation in terms of regions of the spectrum that affected its decision, making it no longer a black box. These regions coincide with those used by human experts, for example relevant spectral lines, and are even used in a similar way; the classifier effectively measures the width of a line by weighing its center and its tails oppositely.

EUV Beam-Foil Spectra of Titanium, Iron, Nickel, and Copper

Beam–foil spectroscopy offers the efficient excitation of the spectra of a single element as well as time-resolved observation. Extreme-ultraviolet (EUV) beam–foil survey and detail spectra of Ti, Fe, Ni, and Cu are presented, as well as survey spectra of Fe and Ni obtained at an electron beam ion trap. Various details are discussed in the context of line intensity ratios, yrast transitions, prompt and delayed spectra, and intercombination transitions.

Assessment of filtered cameras for quantitative 2D analysis of divertor conditions during detachment in JET L-mode plasmas

Estimates for 2D distributions of electron temperature, , electron density, , and atomic deuterium density, , in the JET divertor volume have been inferred from deuterium Balmer line intensity ratios obtained from tomographic reconstructions of divertor camera measurements. This enables also investigation of ionization, , and recombination, , rates. The analysis shows a decrease of to 0.5–1.0 throughout the outer divertor during detachment in low-confinement (L-mode) plasmas. Simultaneously, the high- region and the distribution in the outer divertor are observed to elongate and shift from the outer strike point towards the X-point. The observations are in qualitative agreement and follow the same sequence with modelling predictions of EDGE2D-EIRENE simulations of a density scan. While the method was found to provide good representation of the evolution of volumetric recombination during detachment, in agreement with the simulations, the movement of the ionization front upstream could not be followed due to lack of spatial overlap between the ionization region and the necessary emission distributions. Consequently, the representation of the ionization conditions and the particle balance in the detached outer divertor are compromised.

Chemical abundances in seven metal-poor H ii regions and a determination of the primordial helium abundance

ABSTRACT We conducted a long-slit spectrophotometry analysis to obtain the chemical abundances of seven metal-poor H ii regions in three galaxies: UM 160, UM 420, and TOL 0513−393. The data have been taken with the Focal Reducer Low Dispersion Spectrograph 1 (FORS1) at the 8.2-m Very Large Telescope. We derived the physical conditions and the chemical abundances of N, O, Ne, S, Ar, and Cl. We also performed a detailed analysis that involves abundance determinations using the t2 formalism. Based on He i recombination line intensity ratios, together with the {\sc HELIO 14} code, we derived the abundance of He. In addition, for a value $\Delta Y/\Delta Z_O \rm =3.3\pm 0.7$, we have estimated that the primordial helium abundance by mass is YP = 0.2448 ± 0.0033. This value agrees with values derived from Standard Big Bang Nucleosynthesis and with other recent determinations of YP.

Real-Time Monitoring of Laser Cleaning for Hot-Rolled Stainless Steel by Laser-Induced Breakdown Spectroscopy

Laser cleaning is a competitive alternative to ablate and remove the hard oxide layer on hot-rolled stainless steel. To meet the practical demand, laser-induced breakdown spectroscopy (LIBS) was applied for real-time monitoring of the cleaning process in this study. Furthermore, the as-received and laser cleaned surfaces were characterized by an optical micrograph, an X-ray diffractometer, and a laser scanning confocal microscope. The results showed the relative intensity ratio (RIR) of the FeI emission line at 520.9 nm and the CrI emission line at 589.2 could be a quantitative index to monitor the cleaning process. When the oxide layer was not fully cleaned, the LIBS signals of the substrate were not excited, and the ratio was almost invariant as the power of the laser increased. However, it sharply increased once the oxide layer was effectively cleaned, the cleaned surface was bright, and the surface roughness was smaller in this case. Subsequently, as the surface was over-cleaned with the further increase of laser power, the RIR value remained large. The optimal laser cleaning parameters obtained by the monitoring were determined to avoid re-oxidation and reduce the roughness of the cleaned surface.

Estimation of plasma parameters in a pre-breakdown ionization wave at the glow discharge ignition in argon

The results of an experimental study of a pre-breakdown (slow) ionization wave (IW) in argon-filled discharge tubes of 15 mm i.d. and 80 and 100 cm length at a pressure of 1 and 4 Torr are presented. The breakdown and the IW were initiated by a positive voltage pulse with an amplitude of 2 and 4 kV. The IW was detected by the light emitted from its front. The IW emission spectrum consisted of the argon atomic and ion lines. The Ar(763.5 nm) and Ar+(488.0 nm) lines were used to retrieve the electric field strength value in the IW front. For this, the intensity ratio of these lines was measured. The upper levels for these lines are excited by electron impact, and, due to a large difference between their excitation energies, this ratio strongly depends on the reduced electric field strength E/N (E is the electric field strength, N is the atom number density). Theoretical modeling makes it possible to find a relation between the line intensity ratio and the E/N value. In the model, the axial profile of the IW electric field is approximated by a rectangle with a width determined from the measured emission intensity waveform and the wave velocity. As a result, the E/N magnitude in the IW front was found for various positions along the tube. Emission intensity of the DC discharge was also measured, which allowed us to estimate the emitting level population and electron number density in the IW front. The density of seed electrons ahead of the wave is also evaluated and processes responsible for the appearance of these electrons are discussed.

Spectroscopic Investigation of Laser-Produced Strontium Plasma Using Fundamental and Second Harmonics of Nd:YAG Laser

In the present work, our main focus is to find out an optical window where the plasma is optically thin and the plasma parameters can be determined more reliably. The strontium plasma was generated using the fundamental (1064 nm) and the second harmonic (532 nm) of a Q-switched Nd:YAG laser. The spectra were registered using a set of five miniature spectrometers covering the spectral range from 200 to 720 nm. The intensity ratios of some specific lines have been compared with the theoretically calculated intensities to check the validity of optically thin plasma, free from self-absorption and in local thermodynamic equilibrium. In the selected optical window, the electron number densities have been determined from the Stark broadened line profiles, and the excitation temperatures have been calculated using the Boltzmann plot method for 1064- and 532-nm laser wavelengths. The variations in the electron number density and excitation temperature have been studied as a function of laser energy (8-100 mJ), atmospheric pressure (100-600 mbar), and spatial distribution of the plasma plume (0.5-4.0 mm) for both the lasers. The electron number density is found to be higher for the 532-nm laser than the 1064-nm laser, while the excitation temperature is higher for the 1064-nm laser than the 532-nm laser. We have fitted a power law on the experimental data to analyze the varying trends of excitation temperature.