Band Lines Research Articles

Helium Abundance of the Sun: A Spectroscopic Analysis

Determining the He/H ratio in cool stars presents a fundamental astrophysical challenge. While this ratio is established for hot O and B stars, its extrapolation to cool stars remains uncertain due to the absence of helium lines in their observed spectra. We address this knowledge gap by focusing on the Sun as a representative cool star. We conduct spectroscopic analyses of the observed solar photospheric lines by utilizing a combination of MgH molecular lines and neutral Mg atomic lines including yet another combination of CH and C2 molecular lines with neutral C atomic lines. Our spectroscopic analyses were further exploited by adopting solar model atmospheres constructed for distinct He/H ratios to determine the solar photospheric helium abundance. The helium abundance is determined by enforcing the fact that for an adopted model atmosphere with an appropriate He/H ratio, the derived Mg abundance from the neutral Mg atomic lines and that from the MgH molecular lines must be the same. The same holds for the C abundance derived from neutral C atomic lines and that from CH lines of the CH molecular band and C2 lines from the C2 Swan band. The estimated He/H ratio for the Sun is discussed based on the one-dimensional local thermodynamic equilibrium model atmosphere. The helium abundance (He/H = 0.091−0.014+0.019 ) obtained for the Sun serves as a critical reference point to characterize the He/H ratio of cool stars across the range in their effective temperature.

A Novel Model for the MeV Emission Line in GRB 221009A

Gamma-ray bursts (GRBs) have long been considered potential sources of ultrahigh-energy cosmic rays (UHECRs; with energy ≳1018 eV). In this work, we propose a novel model generating MeV emission lines in GRBs, which can constrain the properties of heavy nuclei that potentially exist in GRB jets. Specifically, we find that relativistic hydrogen-like high-atomic-number ions originating from the β decay of unstable nuclei and/or the recombination entrained in the GRB jet can generate narrow MeV emission lines through the de-excitation of excited electrons. This model can successfully explain the MeV emission line observed in the most luminous GRB ever recorded, GRB 221009A, with suitable parameters including a Lorentz factor γ ∼ 820–1700 and a total mass of heavy nuclei M tot ∼ 1023–1026 g. Especially, the emission line broadening can be reasonably attributed to both the expansion of the jet shell and the thermal motion of nuclei, naturally resulting in a narrow width (σ line/E line ≲ 0.2) consistent with the observation. Furthermore, we predict that different GRBs can exhibit lines in different bands with various evolving behaviors, which might be confirmed with further observations. Finally, our model provides indirect evidence that GRBs may be one of the sources of UHECRs.

PHANGS-ML: Dissecting Multiphase Gas and Dust in Nearby Galaxies Using Machine Learning

The PHANGS survey uses Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, Very Large Telescope, and JWST to obtain an unprecedented high-resolution view of nearby galaxies, covering millions of spatially independent regions. The high dimensionality of such a diverse multiwavelength data set makes it challenging to identify new trends, particularly when they connect observables from different wavelengths. Here, we use unsupervised machine-learning algorithms to mine this information-rich data set to identify novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we extract properties pertaining to their stellar populations; warm ionized and cold molecular gas; and polycyclic aromatic hydrocarbons (PAHs), as measured over 150 pc scale regions. We show that we can divide the regions into groups with distinct multiphase gas and PAH properties. In the process, we identify previously unknown galaxy-wide correlations between PAH band and optical line ratios and use our identified groups to interpret them. The correlations we measure can be naturally explained in a scenario where the PAHs and the ionized gas are exposed to different parts of the same radiation field that varies spatially across the galaxies. This scenario has several implications for nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests significant self-regulation in the interstellar medium, (ii) the PAH 11.3/7.7 μm band ratio may be used to constrain the shape of the non-ionizing far-ultraviolet to optical part of the radiation field, and (iii) the varying radiation field affects line ratios that are commonly used as PAH size diagnostics. Neglecting this effect leads to incorrect or biased PAH sizes.

Spectral profile of ro-vibrational transitions of HCl broadened by He, Ar and SF6: Testing the β-correction to the Hartmann-Tran profile and the speed dependent (complex) hard collision model

The β-correction to the Hartmann-Tran (HT) profile, recently introduced to model the spectral shape of a molecular transition strongly affected by the Dicke narrowing effect (Konefal et al., JQSRT 242 (2020) 106,784), the HT profile (Ngo et al., JQSRT 129 (2013) 89), and the speed dependent (complex) hard collision model (SDcHC, in which the velocity changing collision rate is characterized by a complex number) are tested using spectra of two rovibrational lines of HCl. The R(5) and R(9) lines of the fundamental band of HCl broadened by He, Ar and SF6 have been recorded with a difference-frequency laser spectrometer for total pressures ranging from 12 to 930 mbar. These lines, measured in large pressure ranges with different collision-partners provide a meaningful test of the above-mentioned line-shape models. The results confirm that non-Voigt effects are significant for HCl broadened by Ar and SF6 and mainly due to the large influence of the Dicke narrowing effect. For HCl-SF6 and HCl-Ar, especially for the R(9) line, using the β-correction together with the HT profile (and with the speed-dependent hard collision model, SDHC) significantly improves the fit residuals while it has no effect on (or tends to deteriorate) the quality of the fit for HCl-He and for the R(5) line of HCl-SF6, for which the influence of velocity changing collisions is smaller. Except for HCl-He, the SDcHC model leads to better quality of fit compared to the HT profile. The results also show that numerical correlations between refined line-shape parameters of the HT profile are important and can lead to ill-determined parameters while they are more properly determined with the SDcHC model.

Analysis of Influence Factors and Influence Law of Scattering Electric Field of High Voltage Transmission Line in Short Wave Frequency Band

Analysis of Influence Factors and Influence Law of Scattering Electric Field of High Voltage Transmission Line in Short Wave Frequency Band

Measuring Hydrogen-to-Helium Ratio in Cool Stars

Conventionally, the helium-to-hydrogen ratio for the stars are adopted to be 0.1, as standard, unless, the stars are severely deficient in hydrogen like in RCB-class, or the stars’ helium abundance is accurately measured using He I transitions in warm/hotter stars. In our study, the small change in helium-to-hydrogen ratio (from standard value, 0.1) in normal giants were detected from the large difference (> 0.3 dex) in the Mg-abundance measured from Mg I lines and the subordinate lines of (0,0) MgH band. These are the stars that are mildly hydrogen-deficient/He-enhanced. Such stars were spectroscopically discovered for the first time among giants of the globular cluster ω Centauri. The sample selection, observations, methodoloy and results are discussed in detail.

Application of TDLAS for measuring absorption coefficients of H2S rotational absorption lines near the wavelength of 2 µm

This paper presents the experimental measurement of hydrogen sulfide absorption coefficients in the pressure range of 75–460 mbar of two rotational absorption lines of the vibrational band of H2S molecule at 021-000 transition using the tunable diode laser absorption spectroscopy technique. The obtained results are compared with the data of the HITRAN spectroscopic database.

A new species of Nemophora from Korea (Lepidoptera, Adelidae, Adelinae).

A new species of the genus Nemophora Hoffmannsegg, Nemophora lutea Ko & Hirowatari sp. nov. is described from Korea, which is very similar to N. smaragdaspis (Meyrick) found in India and Nepal but distinguished by its the straight deep orange median band and metallic white lines on the forewing in both sexes. Illustrations of adults and genitalia are provided, with habitat information.

Novel fatigue life prediction approach combined with rain‐flow cycle counting process for random multiaxial non‐proportional loading

AbstractThis study extends an existing fatigue life prediction approach for constant multiaxial non‐proportional loading, which is based on a material constant and non‐proportional factor of the loading path, to random amplitude loading waveforms and combines it with the rain‐flow cycle counting method. To validate the accuracy of the extended fatigue life prediction approach, fatigue tests under constant and random uniaxial and non‐proportional loading conditions were conducted. Moreover, fatigue limit reduction under constant non‐proportional loading was investigated through crack and dislocation structure observations. Then, fatigue lives under random multiaxial non‐proportional loading conditions were evaluated using the extended approach. According to the results, almost all evaluated failure data were distributed within two‐factor band lines, indicating that the extended approach could accurately evaluate the fatigue life of the study material.

Lamb Dip of a Quadrupole Transition in H_{2}.

The saturated absorption spectrum of the hyperfineless S(0) quadrupole line in the (2-0) band of H_{2} is measured at λ=1189 nm, using the NICE-OHMS technique under cryogenic conditions (72K). It is the first time that a Lamb dip of a molecular quadrupole transition has been recorded. At low (150-200W) saturation powers a single narrow Lamb dip is observed, ruling out an underlying recoil doublet of 140kHz. Studies of Doppler-detuned resonances show that the redshifted recoil component can be made visible for low pressures and powers, and prove that the narrow Lamb dip must be interpreted as the blue recoil component. A transition frequency of 252 016 361 164 (8)kHz is extracted, which is off by -2.6 (1.6)MHz from molecular quantum electrodynamical calculations therewith providing a challenge to theory.

Regularization analysis of the strong discontinuity-Cosserat finite element method for modeling strain localization in cohesive-frictional materials by spectral theory

An inappropriate numerical approach adopted for modeling the strain localization of geomaterials often leads to ill-posed boundary value problems (BVP). In this article, we apply spectral analysis to study the regularization mechanism of Cosserat finite element method (CFEM) and strong discontinuity-Cosserat FEM (SD-CFEM). The 1D shear layer model and 2D plane strain tests are modeled to conduct the diagnostic spectral analysis. A 2D slope problem is simulated to demonstrate the effectiveness of SD-CFEM in simulating the characteristics of progressive deformation in geomaterials. The numerical results show that CFEM and SD-CFEM not only maintain the eigenvalues as positive, but also make the dominant eigenvectors for different mesh densities possess the identical evolution pattern which is the fundemental regularization mechanism of both methods. The deformation patterns reflected by dominant eigenvectors indicate that SD-CFEM is more robust in modeling strain localization/shear band than CFEM and SD-FEM do because the former can reflect the energy dissipation both in the shear band with a constant width and on the slip line in the shear band. It can be concluded from the displacement evolution process in the shear band that SD-CFEM inheriting the merits of CFEM and SD-FEM can physically and mathematically better simulate the whole deformation process of geomaterials from weak discontinuity (strain localization) to strong discontinuity (slip).

Investigation of the multi-spectral line output characteristics of a multi-atmospheric CO2 pulsed laser

We have investigated the multi-spectral line output characteristics of a CO2 pulsed laser at multi-atmospheric pressure. The pulse waveforms, wavelengths, and energies of the output spectral lines and the small-signal gains of the full spectrum were measured at 3, 4, and 6 atm. To explain the experimental results and predict the output at higher pressure, a modified six-temperature multi-frequency dynamic model of the regular and sequence band lines was developed. The output spectrum varying from the 10P to 9R band with the increase of pressure was studied theoretically and experimentally. In addition, the gains of the 9R(16), 9P(16), 10R(16), and 10P(16) lines at 3 to 14 atm were simulated and measured, providing insights into variation regulation of the four band gains as pressure increases.

Line positions and intensities of the ν1 band of 12CH3I using mid-infrared optical frequency comb Fourier transform spectroscopy

We present a new spectral analysis of the ν1 and ν3+ν1−ν3 bands of 12CH3I around 2971 cm−1 based on a high-resolution spectrum spanning from 2800 cm–1 to 3160 cm–1, measured using an optical frequency comb Fourier transform spectrometer. From this spectrum, we previously assigned the ν4 and ν3+ν4−ν3 bands around 3060 cm–1 using PGOPHER, and the line list was incorporated in the HITRAN database. Here, we treat the two fundamental bands, ν1 and ν4, together with the perturbing states, 2ν2+ν3 and ν2+2ν6±2, as a four-level system connected via Coriolis and Fermi interactions. A similar four-level system is assumed to connect the two ν3+ν1−ν3 and ν3+ν4−ν3 hot bands, which appear due to the population of the low-lying ν3 state at room temperature, with the 2ν2+2ν3 and ν2+ν3+2ν6±2 perturbing states. This spectroscopic treatment provides a good global agreement of the simulated spectra with experiment, and hence accurate line lists and band parameters of the four connected vibrational states in each system. It also allows revisiting the analysis of the ν4 and ν3+ν4−ν3 bands, which were previously treated as separate bands, not connected to their ν1 and ν3+ν1−ν3 counterparts. Overall, we assign 4665 transitions in the fundamental band system, with an average error of 0.00071 cm–1, a factor of two better than earlier work on the ν1 band using conventional Fourier transform infrared spectroscopy. The ν1 band shows hyperfine splitting, resolvable for transitions with J ≤ 2 × K. Finally, the spectral intensities of 65 lines of the ν1 band and 7 lines of the ν3+ν1−ν3 band are reported for the first time using the Voigt line shape as a model in multispectral fitting. The reported line lists and intensities will serve as a reference for high-resolution molecular spectroscopic databases, and as a basis for line selection in future monitoring applications of CH3I.

Machine Learning-Based Framework for Predicting Creep Rupture Life of Modified 9Cr-1Mo Steel

Efficient and accurate predictions of creep rupture life are essential for ensuring the integrity of high-temperature components. In this work, a machine learning-based framework is developed for the quick screening of crucial features and accurate prediction of the creep rupture life of modified 9Cr-1Mo steels. A feature screening protocol based on correlation filtering and sequential feature selection techniques is established for identifying critical features that significantly affect the prediction performance from a set of numerous descriptors. Moreover, several machine learning algorithms are employed for model training to examine their ability to map the complex nonlinear interactions between multivariate features and creep life. The results show that the test stress, test temperature, tempering time, and the contents of S and Cr are identified as the crucial features that greatly influence the life prediction performance of modified 9Cr-1Mo steels. Moreover, the Gaussian process regression (GPR) model with these five selected crucial features exhibits the highest prediction accuracy among various machine learning strategies. Finally, an additional dataset out of model training and testing is used to further validate the efficacy of the constructed GPR model. The validated results demonstrate that most creep data are distributed inside the two-factor band lines. Results from this work show that the developed machine learning framework can offer high accuracy and excellent adaptability in predicting the creep life of modified 9Cr-1Mo steels under various environmental conditions.

Pressure broadening in Raman spectra of CH4–N2, CH4–CO2, and CH4–C2H6 gas mixtures

Different molecular environments change the spectrum of a given gas sample involved in a mixture compared to the spectrum of a pure gas. It is necessary to account for this effect to improve the accuracy of the analysis of the natural gas composition by Raman spectroscopy. First, the change in the main components of natural gas (methane, nitrogen, carbon dioxide, and ethane) must be considered. This work is devoted to the mutual influence of CH4–N2, CH4–CO2, and CH4–C2H6 on their characteristic Raman bands in the range of 300–2500 cm−1. The half-width and asymmetry of the Q branches of N2, CO2, and C2H6 as a function of methane concentration were obtained in the range of 1–50 bar. The averaged broadening coefficients of the rotational-vibrational lines of the ν2 band of CH4 perturbed by N2, CO2, and C2H6 are measured. A high-sensitivity spectrometer with a resolution of 0.5 cm−1 based on spontaneous Raman scattering was used to obtain reliable results. The algorithm and all the necessary parameters for simulating the effect of various molecular environments on the Raman bands of the main components of natural gas are presented.

Investigations on Pressure Broadening Coefficients of NO Lines in the 1←0 Band for N2, CO2, Ar, H2, O2 and He

A tunable diode laser absorption spectroscopy (TDLAS)-based spectrometer employing a mid-infrared (Mid-IR) interband cascade laser (ICL) was developed and used to determine pressure broadening coefficients of two NO absorption transitions at 1914.98 cm−1 and 1915.76 cm−1 in the fundamental (1←0) band (R11.5 Ω1/2 and Ω3/2) for CO2, N2, Ar, O2, He, and H2. For the first time, a reliable and consistent set of six different pressure-broadening coefficients for the NO line has been measured by a consistent approach covering pressures from 100 to 970 mbar at a temperature of 294 K. Air pressure broadening has been calculated based on N2 and O2 coefficients. The stated pressure-broadening coefficients for N2, CO2, Ar, H2, O2, He, and Air have relative errors in the 0.5–1.5% range. For CO2 and H2, broadening results of NO (1←0) band (R11.5 Ω1/2 and Ω3/2) lines are reported for the first time. The results are also compared to previously available literature data. It was found that the broadening coefficients for O2 and Air are in agreement with literature values, whereas results for Ar and He show larger differences.

The high-accuracy spectroscopy of H2 rovibrational transitions in the (2-0) band near 1.2 μm.

Accurate transition frequencies of six lines of the (2-0) vibrational band of H2 are reported near 1.2 μm, namely Q1-Q4, S0, and S1. These weak electric-quadrupole transitions were measured at room temperature by comb-referenced cavity ring-down spectroscopy. Accurate transition frequencies were determined by applying a multi-spectrum fit procedure with various profile models including speed-dependent collisional broadening and shifting phenomena. Although none of the considered profiles allows reproducing the shape of the strongest lines at the noise level, the zero-pressure line centers are found mostly independent of the used profile. The obtained values are the first H2 (2-0) transition frequencies referenced to an absolute frequency standard. As a result, a 1σ-accuracy better than 100 kHz was achieved for the Q1, S0, and S1 transition frequencies, improving by three orders of magnitude the accuracy of previous measurements. For the six measured transitions, the most recent calculated frequencies were found to be systematically underestimated by about 2.51 MHz, about twice their claimed uncertainties. The energy separation between J = 2 and J = 0 rotational levels of the vibrational ground state was derived from Q2 and S0 transition frequencies and found within the 110 kHz uncertainty of its theoretical value. The same level of agreement was achieved for the energy separation between the J = 3 and J = 1 rotational levels obtained by the difference of Q3 and S1 transition frequencies. The ab initio values of the intensity of the six transitions were validated within a few thousandths.

Observation of Non-Abelian Charged Nodes Linking Nonadjacent Gaps.

Nodal links are special configurations of band degeneracies in the momentum space, where nodal line branches encircle each other. In PT symmetric systems, nodal lines can be topologically characterized using the eigenvector frame rotations along an encircling loop and the linking structure can be described with non-Abelian frame charges involving adjacent bands. While the commutation rules between the frame charges are well established, the underlying relationship between distant band gap closing nodes remains to be explored. In this Letter, we present a photonic multiple nodal links system, where the nodal lines of nonadjacent bands are investigated with symmetry constraints on frame charges. Through an orthogonal nodal chain, the nodal line from the lower two bands predicts the existence of nodal lines formed between the higher bands. We designed and fabricated a metamaterial, with which the multiple nodal links and the topological connection between nonadjacent nodal lines are experimentally demonstrated.

FROM SPECTROSCOPY TO THE CHEMICAL EVOLUTION OF THE GALAXY. PART 1.

A brief review of the results obtained at Odesa Astronomical Observatory based on the stellar spectra analyses from 1892 to 2000 is presented. The review begins with the first observations of emission lines in solar prominences carried out in 1892 under the direction of Alexander Kononowitsch and includes an overview of spectrophotometric studies performed at the observatory using instruments and telescopes designed in- house; theoretical consideration of the issues of modelling physical conditions in stars and spectra simulation. It also describes the main results of the research of stars of various types, including cool giants K-, M spectral types, stars with various peculiarities of chemical composition, having enhanced lines of metals and CN bands, eclipsing binaries and binaries of different types, semi-regular and long-period variable stars, RR Lyraes, δ Scuti and λ Boötes stars, the diversity of Cepheids, blue stragglers in field and cluster populations, hot B Main-Sequence stars, etc., and finally, the enrichment with neutron-capture elements in the galactic stars.

Saturated absorption spectroscopy of HD at 76 K

Precision spectroscopy of molecular hydrogen can be used to test the quantum electrodynamics theory and determine the proton-to-electron mass ratio in a four-body system. Saturated absorption spectroscopy of the R(1) line in the (2-0) band of HD is measured at 76 K. An asymmetric line profile is observed and analyzed, and the transition frequency is predicted to be $217\phantom{\rule{0.16em}{0ex}}105\phantom{\rule{0.16em}{0ex}}182\phantom{\rule{0.16em}{0ex}}284\phantom{\rule{0.16em}{0ex}}{(11)}_{\mathrm{stat}}{(27)}_{\mathrm{sys}}$ kHz. The value is nine times more accurate than our previous result obtained at room temperature and differs by $6.6\ensuremath{\sigma}$ from the recent result derived with a different line-shape model.