Spectral Lines Research Articles

A novel technology based on Raman spectroscopy for effective differentiation of alanine chiral isomers

In this study, Raman time-domain spectroscopy (R-TDS) was used to record the spectra of β-alanine, D-alanine, L-alanine, and DL-alanine molecules in the Raman shift range of 250–2000 cm−1. Baseline correction and smoothing of the original spectra yielded considerably different scattering peaks for β-alanine than the other three alanine isomers. The positions and intensities of the peaks in the spectra of D-alanine, L-alanine and DL-alanine were very similar, enabling β-alanine to be easily distinguished from the aforementioned isomers based on the Raman spectra. The Raman spectral data of D-alanine, L-alanine and DL-alanine were subjected to variational mode decomposition (VMD), whereby each spectral line was decomposed into four intrinsic mode functions (IMFs). Finally, a grid search-support vector machine (GS-SVM) classification recognition model was established for Raman spectral analysis and classification analysis using the first four IMFs as datasets. VMD-GS-SVM classification had a 96.67 % discriminative accuracy for predicted samples of the three isomers of D-alanine, L-alanine and DL-alanine. The classification recognition accuracy gradually trended downward as the number of mode components increased. The results show that the fast identification model of alanine isomers based on R-TDS and VMD-GS-SVM is effective and feasible, providing an accurate and fast optical measurement solution for the development of novel drugs and quality monitoring of fine chemicals.

White Light Emissive Eu(III) Complexes through Ligand Engineering and their Applications in Cool Near Ultraviolet White Light Emitting Diodes and Thermometer.

In pursuit of enhancing white light quality for SSLapplications, an attempt has been made to design novel imidazo-bipyridyl ligands as an ancillary ligand to obtain multiple emissions (mimic sunlight) in the Eu-complex. By strategically modifying the phenanthroline core with imidazo-bipyridyl incorporation with 1 or 2-Napthyl groups at the C1 position, the excitation spectral line is successfully shifted from Ultraviolet (UV) to near UV/visible spectrum (where the LED emission occurs). The ligands showed greenish blue emission in solid and solution. The analysis revealed that the energy transfer is incomplete, primarily attributed to the proximity of triplet state energy levels to the resonance level of Eu(III) ions as reflected in solvatochromism. These complexes exhibit a unique dual emissive behavior (emitting multi-color) including white light across various solvents. The fabricated white LED showed an excellent color rendering index (CRI ~93 %). Beyond lighting, this distinctive property opens avenues for temperature sensing ([Eu(DBM)31-Naph] shows the highest sensitivity of Sr = 10.97 %, and [Eu(DBM)32-Naph] shows the highest sensitivity of Sr = 5.5 % at 333K) and vapoluminescent studies. This research pioneers the development of these complexes as potential single-component materials for white LEDs, underlining their multifaceted utility in cutting-edge lighting and sensing technologies.

Toward a direct measurement of the cosmic acceleration: The pilot observation of HI 21cm absorption line at FAST

Abstract In this study, we present findings on the detection of neutral atomic hydrogen (HI) 21cm absorption in the spectrum of PKS1413+135 at redshift $z=0.24670041$. The observations were conducted by FAST, with a spectral resolution of 10 Hz, using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10kHz within a 2MHz bandwidth. The goal is to determine the rate of the latest cosmic acceleration by directly measuring the evolution of the redshift of HI 21cm absorption line with Hubble flow towards a common background Quasar over a decade or longer time span. This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift $z < 1$, specifically redshift drift $\dot{z}$ or the SL effect.The measured HI gas column density in this DLA system is approximately equivalent to the initial observation value, considering uncertainties in the spin temperature of a spiral host galaxy. The high signal-to-noise ratio of 57, obtained at a 10kHz resolution, strongly supports the feasibility of using the HI 21cm absorption line in DLA systems to accurately measure the redshift rate at a precision level of around $10^{-10}$ per decade.

Effect of single and double pulse laser-induced breakdown spectroscopy towards steel alloy in different gaseous media

In recent years, laser-induced breakdown spectroscopy (LIBS) technique showed its promising for material analysis, quality control, forensic science, and environmental safety monitoring. Besides, due to its rapid measurement capability and minimal sample-preparation requirements, it is a widely recognized elemental analysis approach used in a variety of study domains. The current work compares spatially resolved single (SP) and double pulse (DP), especially orthogonal DP, setups for LIBS to examine and enhance the limit of detection (LOD) in duplex stainless steels alloy. Using the Boltzmann plot method and the Stark broadening mechanism, the electron temperature and density of local arc plasma are highlighted due to single pulse and orthogonal pre-pulse double pulse configurations. With delay time, the circumstances of arc plasma's local thermodynamic equilibrium (LTE) of emission spectral lines are investigated. The experimental results show that there are significant increases in the spectral intensities of the Fe lines in double pulse LIBS under Ar-gas compared to those under He-gas. Internal standardization was used to create calibration curves for the spectral lines of Cr, Cu, and Mn in the alloy sample for the both studied media. It demonstrated that argon outperforms helium in determining the elemental composition of steel alloys. Furthermore, LOD for SP-LIBS and DP-LIBS in both media were calculated, which showed a higher detection LOD for DP-LIBS in the presence of Ar-gas compared to that in He-gas.

EMISSA: Exploring millimetre indicators of solar-stellar activity III. Comparison of Ca II indices and millimetre continua in a 3D model atmosphere

Amongst several spectral lines, some of the strongest chromospheric diagnostics are offered by the Ca II H K lines. These lines can be used to gauge the temperature stratification of the atmosphere since the line core and wings are formed in different regions of the solar atmosphere. Furthermore, the Ca II lines act as tracers for the magnetic structure of the solar atmosphere, as the line cores are formed in the upper chromosphere even though they are formed in non-local thermodynamic equilibrium (NLTE). In contrast, the formation of millimetre (mm) continuum radiation occurs under local thermodynamic equilibrium (LTE) conditions. As a result, the brightness temperatures obtained from observations with the Atacama Large Millimetre/Submillimetre Array (ALMA) offer a complementary perspective on the activity and thermal structure of stellar atmospheres. The overall aim is to establish more robust solar/stellar activity indicators using ALMA observations in comparison with classical diagnostics, such as the s index and infrared triplet (IRT) index. We employed the 1.5D radiative transfer codes RH1.5D and advanced radiative transfer (ART) to compute the synthetic spectra for the Ca II lines and the millimetre (mm) continua, respectively. These calculations were performed using an enhanced network atmosphere model, which incorporates non-equilibrium hydrogen ionisation generated by the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) Bifrost code. To account for the limited spatial resolution of ALMA, we simulated the effect using a Gaussian point spread function (PSF). Additionally, we analysed the correlations and slopes of scatter plots between the Ca II indices and mm continuum for the original and degraded resolutions, focusing on the entire simulation box, quiet Sun regions, and enhanced network patches separately. The activity indices generated from these lines could further be used to compare the spectra of Sun-like stars with the solar spectrum. We present a comparative study between synthetic continuum brightness temperature maps at mm wavelengths (0.3 mm to 8.5 mm) and the Ca II activity indices; namely, the s index and infrared triplet (IRT) index. The Ca II activity indices and mm brightness temperatures are weakly correlated at the high resolution, with the highest correlation observed at a wavelength of 0.3 mm, corresponding to ALMA band 10. As the resolution decreases, the correlation consistently increases. Conversely, the slopes exhibit a decreasing trend with increasing wavelength, while the degradation of resolution does not noticeably affect the calculated slopes. As the spatial resolution decreases, the standard deviations of the Ca II activity indices and brightness temperatures decrease, while the correlations between them increase. However, the slopes do not exhibit significant changes. Consequently, these relationships could be valuable for calibrating the mm continuum maps obtained through ALMA observations.

Stellar Population Astrophysics (SPA) with the TNG. Measurement of the He I 10830 angstrom line in the open cluster Stock 2

The precise measurement of stellar abundances plays a pivotal role in providing constraints on the chemical evolution of the Galaxy. However, before spectral lines can be employed as reliable abundance indicators, particularly for challenging elements such as helium, they must undergo thorough scrutiny. Galactic open clusters, representing well-defined single stellar populations, offer an ideal setting for unfolding the information stored in the helium spectral line feature. In this study we characterise the profile and strength of the helium transition at around angstrom in nine giant stars in the Galactic open cluster Stock 2. To remove the influence of weak blending lines near the helium feature, we calibrated their oscillator strengths (loggf ) by employing corresponding abundances obtained from simultaneously observed optical spectra. Our observations reveal that the in all the targets is observed in absorption, with line strengths categorised into two groups. Three stars exhibit strong absorption, including a discernible secondary component, while the remaining stars exhibit weaker absorption. The lines are in symmetry and align with or near their rest wavelengths, suggesting a stable upper chromosphere without a significant systematic mass motion. We find a correlation between the strength and the Ca ii logRpHK index, with a slope similar to that reported in previous studies on dwarf stars. This correlation underscores the necessity of accounting for the stellar chromosphere structure when employing as a probe for the stellar helium abundance. The procedure of measuring the we developed in this study is applicable not only to other Galactic open clusters but also to field stars, and we plan to use it to map the helium abundance across various types of stars in the future.

Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga3+/Ge4+ cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La3Ga5-xGe1+xO14+0.5x composition. Ultrahigh field 71Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO4, four-connected GaO4 and GaO6 polyhedra are probed for the parent La3Ga5GeO14 structure, while one additional spectral feature corresponding to the key (Ga,Ge)2O8 structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge4+-doped La3Ga3.5Ge2.5O14.75 phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga3+/Ge4+ distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature 17O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

Long-term Integration Ability of the Submillimeter Wave Astronomy Satellite (SWAS) Spectral Line Receivers

Abstract The Submillimeter Wave Astronomy Satellite (SWAS) was the first space telescope capable of high spectral resolution observations of terahertz spectral lines. We have investigated the integration ability of its two receivers and spectrometer during five and a half years of on-orbit operation. The C I, O2, H2O and 13CO spectra taken towards all observed Galactic sources were analyzed. The present results are based on spectra with total integration time up to 2.72 × 104 hours (≃ 108 s). The noise in the spectra is shown to be generally consistent with that expected from the radiometer equation, without any sign of approaching a noise floor. This noise performance reflects the extremely stable performance of the passively cooled front end as well as other relevant components in the SWAS instrument throughout its mission lifetime.

Doppler Tomography of the Circumstellar Disk of the Be Star κ Draconis

κ Draconis is a binary system with a classical Be star as the primary component. Its emission-line spectrum consists of hydrogen lines, notably the Hα line with peak intensity ratio (V/R) variations phase-locked with the orbital period P = 61.55 days. Among binaries demonstrating the Be phenomenon, κ Dra stands out as one of a few systems with a discernible mass of its secondary component. Based on more than 200 spectra obtained in 2014–2023, we verified the physical parameters and constructed the mass function. We used part of these data obtained in 2014–2021 to investigate regions in the circumstellar disk of the primary component that emit the Hα line using the Doppler tomography method. The results show that the disk has a non-uniform density distribution with a prominent enhancement at Vy ≈ 99 km s−1 and Vx≈−6 km s−1 that corresponds to a cloud-like source of the double-peaked Hα line profile. We argue that this enhancement’s motion is responsible for the periodic variations in the Hα V/R ratio, which is synchronised in orbital phase with the radial velocity (RV) of absorption lines from the atmosphere of the primary component.

The rotation-tunneling spectrum of 3-hydroxypropenal and confirmation of its detection toward IRAS 16293-2422 B

3-Hydroxypropenal (HOCHCHCHO) is the lower energy tautomer of malonaldehyde which displays a complex rotation-tunneling spectrum. It was detected somewhat tentatively toward the solar-type protostellar system IRAS 16293$-$2422 with ALMA in the framework of the Protostellar Interferometric Line Survey (PILS). Several transitions, however, had large residuals, preventing not only their detection, but also the excitation temperature of the species from being determined unambiguously. We want to extend the existing rotational line list of 3-hydroxypropenal to shed more light on the recent observational results and to facilitate additional radio astronomical searches for this molecule. We recorded and analyzed the rotation-tunneling spectrum of 3-hydroxypropenal in the frequency regions between 150 and 330 GHz and between 400 and 660 GHz. Transitions were searched for in the PILS observations of IRAS 16293$-$2422. Local thermodynamic equilibrium (LTE) models were carried out and compared to the observations to constrain the excitation temperature. Additional transitions were searched for in other ALMA archival data of the same source to confirm the presence of 3-hydroxypropenal. More than 7500 different spectral lines, corresponding to more than 11500 transitions, were assigned in the course of our investigation with quantum numbers $2 J 100$, $K_a 59$, and $K_c 97$, resulting in a greatly improved set of spectroscopic parameters. The comparison between the LTE models and the observations yields an excitation temperature of 125 K with a column density $N = 1.0 $ cm$^ $ for this species. We identified seven additional lines of 3-hydroxypropenal that show a good agreement with the model in the ALMA archive data. The calculated rotation-tunneling spectrum of 3-hydroxypropenal has sufficient accuracy for radio astronomical searches. With the solution of the excitation temperature conundrum and the detection of seven more lines, we consider the detection of 3-hydroxypropenal toward IRAS 16293$-$2422 as secure.

Simultaneous measurement of NH3 and NO by mid-infrared tunable diode laser absorption spectroscopy based on machine-learning algorithms

Accurate measurements of NH3 and NO are essential for controlling NOx emissions from coal-fired power plants, reducing ammonia slip, and improving the efficiency of selective catalytic reduction (SCR) operation. We propose a method for measuring NH3 and NO concentrations based on machine learning algorithms to address the challenges posed by overlapping interference of CO2 and H2O spectral lines in flue gas. Our approach introduces a novel method for acquiring mixture spectra for the model. Initially, we measure the spectra of individual components under different concentrations and temperatures. Subsequently, mixed spectral samples are generated by combining the measured spectra of the individual components. This approach simplifies the spectral measurement process while preserving accuracy. The particle swarm optimization support vector machine (PSO-SVM) algorithm is leveraged, providing a reliable foundation for the continuous and synchronous measurement of NH3 and NO. Upon testing, the PSO-SVM demonstrates average relative errors of 4.0 % and 0.8 % for NH3 and NO concentrations, respectively. The corresponding measurement precision is 0.05 ppm for NH3 and 0.42 ppm for NO, better than the conventional integral absorbance method. The minimum detection limit (MDL) for NH3 is 16.1 ppb at an average time of 50 s, while for NO, it is 38.4 ppb at an average time of 71 s. The methodology of this paper is expected to play an important role in reducing the influence of interfering components and improving the accuracy of field measurements.

Matched Stochastic Resonance Enhanced Underwater Passive Sonar Detection under Non-Gaussian Impulsive Background Noise.

Remote passive sonar detection with low-frequency band spectral lines has attracted much attention, while complex low-frequency non-Gaussian impulsive noisy environments would strongly affect the detection performance. This is a challenging problem in weak signal detection, especially for the high false alarm rate caused by heavy-tailed impulsive noise. In this paper, a novel matched stochastic resonance (MSR)-based weak signal detection model is established, and two MSR-based detectors named MSR-PED and MSR-PSNR are proposed based on a theoretical analysis of the MSR output response. Comprehensive detection performance analyses in both Gasussian and non-Gaussian impulsive noise conditions are presented, which revealed the superior performance of our proposed detector under non-Gasussian impulsive noise. Numerical analysis and application verification have revealed the superior detection performance with the proposed MSR-PSNR detector compared with energy-based detection methods, which can break through the high false alarm rate problem caused by heavy-tailed impulsive noise. For a typical non-Gasussian impulsive noise assumption with α=1.5, the proposed MSR-PED and MSR-PSNR can achieve approximately 16 dB and 22 dB improvements, respectively, in the detection performance compared to the classical PED method. For stronger, non-Gaussian impulsive noise conditions corresponding to α=1, the improvement in detection performance can be more significant. Our proposed MSR-PSNR methods can overcome the challenging problem of a high false alarm rate caused by heavy-tailed impulsive noise. This work can lay a solid foundation for breaking through the challenges of underwater passive sonar detection under non-Gaussian impulsive background noise, and can provide important guidance for future research work.

B0-insensitive image navigators for prospective motion-corrected MRS with localized second-order shimming.

Localized shimming in single-voxel MRS often results in large B0 inhomogeneity outside the volume-of-interest. This causes unacceptable degradation in motion navigator images. Switching back and forth between whole-brain shim and localized shim is possible for linear shims, but not for higher-order shims. Here we propose motion navigators largely insensitive to B0 inhomogeneity for prospective motion-corrected MRS with localized higher-order shimming. A recent fast high-resolution motion navigator based on spiral-in/out k-space trajectories and multislice-to-volume registration was modified by splitting the readout into multiple shot interleaves which shortened the echo time and reduced the effect of B0 inhomogeneity. The performance of motion correction was assessed in healthy subjects in the prefrontal cortex using a sLASER sequence at 3T (N = 5) and 7T (N = 5). With multiple spatial interleaves, excellent quality navigator images were acquired in the whole brain in spite of large B0 inhomogeneity outside the MRS voxel. The total duration of the navigator in sLASER remained relatively short even with multiple shots (3T: 10 spatial interleaves 94 ms per slice; 7T: 15 spatial interleaves 103 ms per slice). Prospective motion correction using the multi-shot navigators yielded comparable spectral quality (water linewidth and metabolite SNR) with and without subject motion. B0-insensitive motion navigators enable prospective motion correction for MRS with all first- and second-order shims adjusted in the MRS voxel, providing optimal spectral linewidth.

Toward an Auditory Virtual Observatory

The large ecosystem of observations generated by major space telescope missions can be remotely analyzed using interoperable virtual observatory technologies. In this context of astronomical big data analysis, sonification has the potential of adding a complementary dimension to visualization, enhancing the accessibility of the archives, and offering an alternative strategy to be used when overlapping issues are found in purely graphical representations. This article presents a collection of sonification and musification prototypes that explore the case studies of the MILES and STELIB stellar libraries from the Spanish Virtual Observatory and the Kepler and TESS light curve databases from the Space Telescope Science Institute archive. Using automation and deep learning algorithms, it offers a “palette” of resources that could be used in future developments oriented toward an auditory virtual observatory proposal. The work includes a user study with quantitative and qualitative feedback from specialized and nonspecialized users analyzing the use of sine waves and musical instrument mappings for revealing overlapped lines in galaxy transmission spectra, confirming the need for training and prior knowledge for the correct interpretation of accurate sonifications, and providing potential guidelines to inspire future designs of widely accepted auditory representations for outreach purposes.

Growing a nuclear star cluster from star formation and cluster mergers: The JWST NIRSpec view of NGC 4654

We present a detailed study of the centre of NGC\,4654, a Milky Way-like spiral galaxy in the Virgo cluster that has been reported to host a double stellar nucleus, thus promising a rare view of ongoing star cluster infall into a galaxy nucleus. Analysing JWST NIRSpec integral-field spectroscopic data in combination with Hubble Space Telescope Wide Field Camera 3 imaging of the inner 330 times 330 pc, we find that the NGC\,4645 nucleus is in fact more complex than previously thought, harbouring three massive star clusters within 32 pc of the centre. Maps of infrared emission lines in the NIRSpec spectra show different morphologies for the ionised and molecular gas components. The emission from molecular hydrogen gas is concentrated at the nuclear star cluster (NSC) location, while emission from hydrogen recombination lines is more extended beyond the central cluster. The velocity fields of both gas and stars indicate that the three clusters are part of a complicated dynamical system, with the NSC having an elevated velocity dispersion in line with its high stellar mass. To investigate the stellar populations of the three clusters in more detail, we used surface brightness modelling to measure their fluxes from UV to mid-infrared wavelengths. This information, together with spectroscopically derived extinction values, are then used to fit the spectral energy distributions (SEDs) of the clusters. Two of the clusters are UV-bright and well described by single stellar populations with young ages (sim 3 and 5 Myr) and relatively low masses ($M_ M_ and $M_ M_ respectively), whereas the central cluster is much more massive ($M_ 10^7 M_ and cannot be fitted by a single stellar population. Instead, we find that the presence of a minor young population (sim 1\,Myr, $M_ M_ embedded in a dominant old population (sim 8\,Gyr) is required to explain its SED. Given its complex composition and the close proximity of two young star clusters that are likely to merge with it within a few hundred million years, we consider the nucleus of NGC\,4654 a unique laboratory to study NSC growth from both in situ star formation and the infall of star clusters.

Quasi-equilibrium chemical evolution in starless cores

Abstract The chemistry of H2O, CO and other small molecular species in an isolated pre-stellar core, L1544, has been assessed in the context of a comprehensive gas-grain chemical model, coupled to an empirically constrained physical/dynamical model. Our main findings are (i) that the chemical network remains in near equilibrium as the core evolves towards star formation and the molecular abundances change in response to the evolving physical conditions. The gas-phase abundances at any time can be calculated accurately with equilibrium chemistry, and the concept of chemical clocks is meaningless in molecular clouds with similar conditions and dynamical time scales, and (ii) A comparison of the results of complex and simple chemical networks indicates that the abundances of the dominant oxygen and carbon species, H2O, CO, C, and C+ are reasonably approximated by simple networks. In chemical equilibrium, the time-dependent differential terms vanish and a simple network reduces to a few algebraic equations. This allows rapid calculation of the abundances most responsible for spectral line radiative cooling in molecular clouds with long dynamical time scales. The dust ice mantles are highly structured and the ice layers retain a memory of the gas-phase abundances at the time of their deposition. A complex (gas-phase and gas-grain) chemical structure therefore exists, with cosmic-ray induced processes dominating in the inner regions. The inferred H2O abundance profiles for L1544 require that the outer parts of the core and also any medium exterior to the core are essentially transparent to the interstellar radiation field.

Negative refractive index enhancement with zero absorption in a concentric chiral metal-atomic nanoshell

We investigate the electromagnetic chirality and negative refraction in a concentric nanoshell of a chiral metal sphere and a chiral atomic shell. The medium of the atomic shell with a four-level system is driven by a laser field and an incoherent pump field in a diamond configuration. We show that the electric and magnetic absorption spectra connecting through the chiral coefficients of the respective dipole moments of the two media, produce five and three lines spectral profiles. We explain that the spectral lines separated by dips are the manifestation of the classical (quantum) coherence effect of the wave field excitation in the medium of the metal sphere (atomic shell), and the interaction of the respective dipole moments at the interface of the two media. Furthermore, we show negative refraction with zero absorption without requiring permittivity (ϵ) and permeability (μ) simultaneously negative, where for all values of the incident wavelength, Re [μ] ≈ 1, representing a strong chiral electromagnetic behavior. Consequently, the negative refractive index enhances sufficiently beyond n = −1 for a wide range of parameters depending on the coupling parameters, chiral coefficients, and the radii ratio of the concentric metal-atomic nanoshell.

Nanosecond repetitively pulsed plasmas with MHz bursts for CO2 dissociation

A novel pulsed power source capable of nanosecond pulses with burst frequencies up to 1 MHz is employed to create atmospheric pressure pulsed plasma in pure CO2 gas. The short bursts contain up to four nanosecond pulses. The CO2 conversion and corresponding energy efficiency are measured ex-situ with Fourier-transform infrared absorption spectroscopy. Trends in the absorption line profile of in-situ quantum cascade laser infrared absorption spectroscopy indicate an elevated vibrational temperature of CO2 with an increasing number of pulses per burst. The key result of this paper is that the dissociation energy efficiency is higher when operating the plasma in burst mode. Furthermore, a larger number of pulses in a burst is associated with a further increase of the dissociation efficiency. The highest efficiency measured is (17.7±0.3) % for single pulses spaced 2 ms apart, and (20.0±0.3) % for bursts of three pulses, with an in-burst frequency of 1 MHz and bursts spaced 4 ms apart.

Simulation of emission of the flare 27.04.2012 in spectral lines of Hydrogen, Helium and Calcium

Тhe article is devoted to analyses of solar flare SOL2012-04-27 emission in Hydrogen, Helium and Calcium spectral lines observed on horizontal solar equipment HSFA-2 in Ondˇrejov observatory. The integrated fluxes are calculated. The data collected are treated in the approach of the fast energy release followed by gas evaporation. The gas parameters are calculated with chromosphere conditions and spectral line self-absorption taken into account. Encompassing of six lines allows to reveal the temperature, density and extent of the gas with high degree of validity. The best agreement of the theory with observations is obtained in the model of the spread of inhomogeneous clouds, each of which has hot (T ≈ 18000 ÷ 19500 K) and cool regions (T ≈ 8000 ÷ 9000 K). On average, one cloud gives about ten percent of the total flux.

Dark matter search in the Perseus cluster with simultaneous analysis of Hitomi and Suzaku data

Abstract The reported detection of a 3.5 keV emission line in the Perseus cluster, possibly originating from dark matter decay, is still under scrutiny. Despite extensive observations, the detection has not yet been confirmed, and its origin remains a topic of active debate. Most of the previous searches relied on spectroscopy with X-ray charge-coupled devices, such as the X-ray Imaging Spectrometer on Suzaku. Although this provided a large amount of observational data, it only offered moderate spectral resolution. The X-ray astronomy satellite Hitomi offers new results using its high-resolution X-ray spectrometer (Soft X-ray Spectrometer). However, the data gathered were somewhat limited in terms of statistics. In this work, we present the results of a new spectral analysis of the Perseus cluster that combines the spectra from the XIS and SXS, along with the Soft X-ray Imager on Hitomi, thereby complementing each other’s capability. Our search was conducted for a line emission or absorption in the energy range of 2.6–5.9 keV assuming the Navarro–Frenk–White mass distribution with a concentration parameter of 5.0 and virial radius, r200, of 1.79 Mpc. We also considered the instrumental systematic uncertainty caused by the effective area calibration, which we empirically evaluated using the Crab Nebula spectra. On combining these results, we found no significant line features above the baryonic thermal emission from the intra-cluster medium. The upper limit at 3.5 keV, at a 3σ confidence level, is tightly constrained to 4.2 × 10−5 photons cm−2 s−1 for the $15^{\prime }$ circular sky region, which encloses a dark matter mass of $1.67\times 10^{14}\, M_{\odot }$, assuming a line velocity dispersion of 180 km s−1. This constraint is three times tighter than the previous one, which only used the SXS. On the basis of these findings, we provide the upper limit of the dark matter decay rate and the mixing angle for the sterile neutrino origin.