Spectral Line Characteristics Research Articles

MK-like spectral classification for hot subdwarf stars with LAMOST spectra

Abstract An MK-like spectral classification has been conducted for 1224 hot subdwarf stars with LAMOST DR9 low-resolution spectra. The whole sample was divided into four categories according to the spectral line characteristics: He-normal, He-weak, He-strong C, and He-strong. Each selected spectrum was assigned a spectral class, a luminosity class, and a helium class by comparing the line depth and width with standard spectra selected in LAMOST. Relationships between atmospheric parameters and spectral classification are also presented.

Measurement method of the transient radiated noise in the reverberant pool

Transient radiated noise is the primary source of exposure for underwater targets due to its short duration and distinct spectral line characteristics. In order to accurately measure the sound source level of transient radiated noise, a reverberation method of radiated noise measurement based on power averaging processing in the frequency band is proposed. The power of the transient signal is obtained by using time-domain signal autocorrelation technology. The sound source level of the transient radiated noise in the frequency range of 500 kHz to 10 kHz is determined by the reverberant characteristics of the pool. The sound source level of the transient radiated noise in the frequency range of 1 kHz - 10 kHz is compared and measured in the anechoic tank. The deviation of the measurement results is less than 1.5 dB, which confirms the accuracy of the reverberant measurement method.

High-Resolution Spectroscopy of the ErCrO<sub>3</sub> Crystal: A New Phase Transition?

Infrared absorption spectra of the ErCrO3crystal in the region off−ftransitions in the Er3+ion are recorded for the first time. An analysis of high-resolution temperature-dependent spectra reveals a step atT′=47K on the temperature dependences of the characteristics of spectral lines, in addition to the features at temperatures of magnetic orderingTN= 133 K and spin-reorientation transitionTSR=9.3K. This feature can be associated with either a previously unknown phase transition or with local changes in the crystal structure. The shape of the lines at liquid helium temperatures indicates the presence of additional positions for Er3+ions in the ErCrO3crystal. Presumably, these are positions near uncontrolled impurities that enter the crystal during its growth by the solution–melt method and form regions with a distorted structure responsible for the occurrence of polarization.

High-Resolution Spectroscopy of the ErCrO3 Crystal: A New Phase Transition?

Infrared absorption spectra of the ErCrO3 crystal in the region of f{-} f transitions in the Er3+ ion are recorded for the first time. An analysis of high-resolution temperature-dependent spectra reveals a step at T{kern 1pt} ' = 47 K on the temperature dependences of the characteristics of spectral lines, in addition to the features at temperatures of magnetic ordering TN = 133 K and spin-reorientation transition {{T}_{{{text{SR}}}}} = 9.3{kern 1pt} K. This feature can be associated with either a previously unknown phase transition or with local changes in the crystal structure. The shape of the lines at liquid helium temperatures indicates the presence of additional positions for Er3+ ions in the ErCrO3 crystal. Presumably, these are positions near uncontrolled impurities that enter the crystal during its growth by the solution–melt method and form regions with a distorted structure responsible for the occurrence of polarization.

Nonlinearity parameter in the pathlength dimension to improve the scattering in the transmission spectra.

In spectrochemical quantitative analysis of solutions containing scattering components, the spectral nonlinearity caused by scattering seriously affects the prediction accuracy, robustness, and even feasibility of the models. Unlike the traditional methods (modeling with the spectra data of single pathlength) of approximating the nonlinear spectral line to linear to reduce the nonlinear features of scattering, a new method is proposed to reduce the effect of scattering by taking advantage of the nonlinear characteristics of spectral lines. First, the logarithmic function is used to fit the attenuation of multiple pathlengths, then the regression coefficient of the function is taken as the characteristic parameter of scattering, and the wavelengths with smaller characteristic parameter are selected as the modeling wavelengths. The model is robust and insensitive to the effect of scattering. The experiment involving a variety of scattering cases containing intralipids and ink was taken to verify the method. An F-test of the experimental results was significant at the 0.05 level. The root mean square error of prediction of the new method was 1.94%, and the prediction accuracy was 75.5% higher than that of the traditional model. The new method provides a novel approach toward describing the spectral nonlinearity with a function.

Quantitative analysis of coal-bed methane components by downhole laser Raman spectroscopy

Laser Raman spectroscopy can be used to acquire the unique fingerprint of a specific molecule, and it is widely used to identify substances and to study the spectral line characteristics of molecular structures. The measurement of coalbed methane (CBM) content is essential in the exploration and development of CBM fields for optimizing the fracture design. For this purpose, laser Raman spectroscopy can be extremely beneficial because it detects the gas content rapidly and accurately. Moreover, conventional gas content testing methods are laborious, time-intensive, and expensive, and they yield inaccurate results. Therefore, we have integrated a laser Raman spectroscopy system with coiled tubing (CT) equipment for downhole deployment in gas wells to accurately determine the CBM content in situ. The developed system can directly determine the CBM content at a specific location in the target layer. The trace test characteristics enable this system to rapidly detect downhole gas components and contents. The real-time detection data are transmitted via a cable to a computer on the surface and are processed using a baseline correction algorithm and a data enhancement algorithm. The Fourier transform and the wavelet transform are used to identify the Raman spectral lines, whereas analysis of Raman spectra is used to determine the CBM content. By using this equipment, we can shorten the cycle of depressurization, drainage, and recovery processes from multiple days to just a few hours. Furthermore, the integrated laser Raman spectroscopy-CT system enables a flexible operation and possesses strong site operability, making it suitable for complex and high-risk wells.

Benchmark stars, benchmark spectrographs

Context. Gaiabenchmark stars are selected to be calibration stars for different spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for these stars are therefore required. We collected ultrahigh-resolution ESPRESSO spectra for 30 of the 34Gaiabenchmark stars and made them public.Aims.We quantify the consistency of the results that are obtained with different high- (R~ 115 000), and ultrahigh- (R~ 220 000) resolution spectrographs. We also comprehensively studied the effect of using different spectral reduction products of ESPRESSO on the final spectroscopic results.Methods.We used ultrahigh- and high-resolution spectra obtained with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line characteristics (line depth; line width; and equivalent width, EW) and determined stellar parameters and abundances for a subset of 11Gaiabenchmark stars. We used the ARES code for automatic measurements of the spectral line parameters.Results.Our measurements reveal that the same individual spectral lines measured from adjacent 2D (spectrum in the wavelength-order space) echelle orders of ESPRESSO spectra differ slightly in line depth and line width. When a long list of spectral lines is considered, the EW measurements based on the 2D and 1D (the final spectral product) ESPRESSO spectra agree very well. The EW spectral line measurements based on the ESPRESSO, PEPSI, and HARPS spectra also agree to within a few percent. However, we note that the lines appear deeper in the ESPRESSO spectra than in PEPSI and HARPS. The stellar parameters derived from each spectrograph by combining the several available spectra agree well overall.Conclusions.We conclude that the ESPRESSO, PEPSI, and HARPS spectrographs can deliver spectroscopic results that are sufficiently consistent for most of the science cases in stellar spectroscopy. However, we found small but important differences in the performance of the three spectrographs that can be crucial for specific science cases.

Jet–ISM interactions near the microquasars GRS 1758−258 and 1E 1740.7−2942

ABSTRACT We present Atacama Large Millimeter/Sub-millimeter Array observations of the candidate jet–ISM interaction zones near the black hole X-ray binaries GRS 1758−258 and 1E 1740.7−2942. Using these data, we map the molecular line emission in the regions, detecting emission from the HCN [J = 1−0], HCO+ [J = 1−0], SiO [J = 2−1], CS [J = 2−1], 13CO [J = 1−0], C18O [J = 1−0], HNCO [J = 40,4−30,3], HNCO [J = 50,5−40,4], and CH3OH [J = 21,1−11,0] molecular transitions. Through examining the morphological, spectral, and kinematic properties of this emission, we identify molecular structures that may trace jet-driven cavities in the gas surrounding these systems. Our results from the GRS 1758−258 region in particular, are consistent with recent work, which postulated the presence of a jet-blown cocoon structure in deep radio continuum maps of the region. Using these newly discovered molecular structures as calorimeters, we estimate the time averaged jet power from these systems, finding $(1.1{\!-\!}5.7)\times 10^{36}{\rm erg\, s}^{-1}$ over 0.12−0.31 Myr for GRS 1758−258 and $(0.7{\!-\!}3.5)\times 10^{37}{\rm erg\, s}^{-1}$ over 0.10−0.26 Myr for 1E 1740.7−2942. Additionally, the spectral line characteristics of the detected emission place these molecular structures in the central molecular zone of our Galaxy, thereby constraining the distances to the black hole X-ray binaries to be 8.0 ± 1.0 kpc. Overall, our analysis solidifies the diagnostic capacity of molecular lines, and highlights how astro-chemistry can both identify jet–ISM interaction zones and probe jet feedback from Galactic X-ray binaries.

3D Realistic Modeling of Solar-Type Stars to Characterize the Stellar Jitter

AbstractDetection of Earth-mass planets with the radial velocity method requires a precision of about 10cm/s to identify a signal caused by such a planet. At the same time, noise originating in the photospheric and subphotospheric layers of the parent star is of the order of meters per second. Understanding the physical nature of the photospheric noise (so-called stellar jitter) and characterizing it are critical for developing techniques to filter out these unwanted signals. We take advantage of current computational and technological capabilities to create 3D realistic models of stellar subsurface convection and atmospheres to characterize the photospheric jitter. We present 3D radiative hydrodynamic models of several solar-type target stars of various masses and metallicities, discuss how the turbulent surface dynamics and spectral line characteristics depend on stellar properties, and provide stellar jitter estimates for these stars.

Temperature diagnostics for Z-pinches plasma in dependence on compression degree

AbstractCalculations of the spectral coefficients for X-ray absorption and spectral brightness's for X-ray radiation were performed for niobium Z-pinch plasma at the temperature of 1 keV and at different plasma densities to determine the compression degree where the spectral lines become indistinguishable. As known, traditional methods of temperature diagnostics of hot dense radiating plasmas are based on analysis of the spectral line shape in dependence on plasma temperature and density. In this case, the interval of photon radiation energies is used, where the spectral lines are well distinguishable in an experiment. On the other hand, Z-pinch plasma has high compression, and an increase of plasma density leads to the deformation of the spectral line shape because of Doppler broadening, Stark broadening, and so-called “additional” broadening of spectral lines that take place in a quantum statistical ensemble of plasma ions and atoms. The traditional method of temperature diagnostics becomes impossible and different methods, which do not use spectral line characteristics, should be applied. The aim of this paper is to determine the density border where the spectral lines become indistinguishable. Important features of the quantum mechanical model, which is known as ion model of plasma, and which is used for calculations in the presented paper, are considered and discussed. A brief review of the theoretical models that have been earlier developed to calculate the radiative opacity characteristics of hot dense plasma is presented as well.

Coherent population trapping spectral line characteristics for high sensitivity magnetic field measurement

Abstract The coherent population trapping (CPT) phenomenon of atoms is used for high precision measurement of weak magnetic field. The sensitivity of the measurement is mainly affected by the resonance spectrum characteristics when this phenomenon occurs. Signal quality factor is defined to represent the characteristics of the CPT resonance signal. Its variation with temperature of the atomic chamber is analyzed and compared with signal contrast. Results show that signal quality factor and signal contrast offer different optimal working temperature which corresponding to the maximum value. The optimal temperature proposed by the signal quality factor is always lower and it makes the magnetic field measurement system to obtain a higher sensitivity.

Using stellar spectra to illustrate thermal radiation laws

Stars are point-source emitters that are the closest to the definition of a blackbody in comparison to all other similar sources of radiation found in nature. Existing libraries on stellar spectra are thus a valuable resource that can be used to introduce the laws of thermal radiation in a classroom setting. In this article we briefly describe some of the opportunities that available databases on stellar spectra provide for students to gain a deeper understanding on thermal radiation and spectral line characteristics.

Characteristics of spectral lines with crater development during laser-induced breakdown spectroscopy

To study the characteristics of spectral lines with crater development during laser-induced breakdown spectroscopy, the changes in the spectral line intensities of iron (Fe) and chromium (Cr) during the development of craters were investigated. Images of the plasmas formed during crater development were captured, and the temperatures and electron densities of the plasmas were calculated. The results showed that when a crater developed, the intensities of the ion lines decreased and the intensities of the atomic lines increased. This is because the plasmas generated in the crater have a higher initial emission intensity and experience more rapid cooling as the crater develops. These two effects lead to changes in the rates of decrease of ion and atomic line intensities over time. Therefore, the changes in intensities of ion lines caused by crater development differ from which of atomic lines.

A Study on the Characteristics of Carbon-Related Spectral Lines from a Laser-Induced Fly Ash Plasma**supported by National Natural Science Foundation of China (Nos. 51071069 and 51476061), Guangdong Province Key Laboratory of Efficient and Clean Energy Utilization, China (No. 2013A061401005) and Key Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes of China (No. KLB10004)

A 1064 nm Nd:YAG laser was used to ablate fly ash samples. The characteristics of the spectral lines measured from the laserablated fly ash plasmas are presented with special attention to atomic and molecular carbon emission. It is shown that the intensity of the atomic line C I 192.9 nm is weak and the shot-to-shot intensity is fluctuant. The carbon atomic line C I 247.7 nm is relatively intensive and stable, however it is seriously interfered with by Fe I 247.8 nm. The intensity of the CN molecular line is close to that of C I 247.7 nm and the CN line is stable and less interfered with. The comparison of molecular CN emission under different conditions (air, Ar and N2) shows that the CN lines detected from the plasmas formed in an atmospheric environment are correlated with the reaction of carbon atoms in the plasma with the nitrogen in air, which indicates that the CN line is also important in pulsed laser ablation fly ash plasmas and this information can be incorporated in the detection of unburned carbon content in fly ash. Finally, a calibration curve is established with a correlation coefficient R2 of 0.999, using C I 247.7 nm and the CN molecular line as associated variables. In addition, accuracy is improved to a certain extent.

Laser-induced Breakdown spectroscopy quantitative analysis method via adaptive analytical line selection and relevance vector machine regression model

Abstract A new LIBS quantitative analysis method based on analytical line adaptive selection and Relevance Vector Machine (RVM) regression model is proposed. First, a scheme of adaptively selecting analytical line is put forward in order to overcome the drawback of high dependency on a priori knowledge. The candidate analytical lines are automatically selected based on the built-in characteristics of spectral lines, such as spectral intensity, wavelength and width at half height. The analytical lines which will be used as input variables of regression model are determined adaptively according to the samples for both training and testing. Second, an LIBS quantitative analysis method based on RVM is presented. The intensities of analytical lines and the elemental concentrations of certified standard samples are used to train the RVM regression model. The predicted elemental concentration analysis results will be given with a form of confidence interval of probabilistic distribution, which is helpful for evaluating the uncertainness contained in the measured spectra. Chromium concentration analysis experiments of 23 certified standard high-alloy steel samples have been carried out. The multiple correlation coefficient of the prediction was up to 98.85%, and the average relative error of the prediction was 4.01%. The experiment results showed that the proposed LIBS quantitative analysis method achieved better prediction accuracy and better modeling robustness compared with the methods based on partial least squares regression, artificial neural network and standard support vector machine.

A 1.3 cm line survey toward IRC +10216

IRC +10216 is the prototypical carbon star exhibiting an extended molecular circumstellar envelope. Its spectral properties are therefore the template for an entire class of objects. The main goal is to systematically study the $\lambda$ $\sim$1.3 cm spectral line characteristics of IRC +10216. We carried out a spectral line survey with the Effelsberg-100 m telescope toward IRC +10216. It covers the frequency range between 17.8 GHz and 26.3 GHz (K-band). In the circumstellar shell of IRC +10216, we find 78 spectral lines, among which 12 remain unidentified. The identified lines are assigned to 18 different molecules and radicals. A total of 23 lines from species known to exist in this envelope are detected for the first time outside the Solar System and there are additional 20 lines first detected in IRC +10216. The potential orgin of "U" lines is also discussed. Assuming local thermodynamic equilibrium (LTE), we then determine rotational temperatures and column densities of 17 detected molecules. Molecular abundances relative to H$_{2}$ are also estimated. A non-LTE analysis of NH$_{3}$ shows that the bulk of its emission arises from the inner envelope with a kinetic temperature of 70$\pm$20 K. Evidence for NH$_{3}$ emitting gas with higher kinetic temperature is also obtained, and potential abundance differences between various $^{13}$C-bearing isotopologues of HC$_{5}$N are evaluated. Overall, the isotopic $^{12}$C/$^{13}$C ratio is estimated to be 49$\pm$9. Finally, a comparison of detected molecules in the $\lambda$ $\sim$1.3 cm range with the dark cloud TMC-1 indicates that silicate-bearing molecules are more predominant in IRC +10216.

Indications of shock waves in the solar photosphere

High resolution observations of solar granulation near the solar limb are used in a search for hydrodynamic shocks caused by an abrupt braking of the fast (probably supersonic) horizontal flow of the granular plasma towards the intergranular lane. Shock signatures in the spectral line of Fe II 6456.38 A of one particular observed shock event are investigated in detail. Evolution, amplitude, and spatial relation of the spectral line characteristics of the shock event are in agreement with predictions from numerical simulations for such shock phenomena in the solar photosphere. The dimensions and amplitudes of the observed shock signatures are comparable to predicted values when seeing and instrumental effects as well as a possible obliqueness of the shock front with respect to the observer's line-of-sight are taken into account. The temporal evolution of such an event is observed for the first time. The stable and declining phase of the event were studied for a time period of almost 2 min. A particular relationship was found between the shock event and a nearby G-band bright point located 2 �� from the shock event. It is suggestive that the observed shock is a causal consequence of the magnetic flux concentration, traced by the G-band bright point. Such a type of shock can appear outside the flux concentrations as a consequence of a rapid flux-tube motion.

Precise reduction of solar spectra obtained with large CCD arrays

A precise procedure suitable for the reduction of solar spectra taken with large CCD arrays and the retrieval of correct spectral characteristics is presented. Various effects, which one should take into account, are considered and several improvements of the standard reduction are introduced. A special flat-field procedure is suggested for the reduction of spectra registered in different flat-field conditions than those when the flat-field matrix was taken. The original flat-field matrix is split into several components to eliminate the influence of the drift of the spectrograph and temporal changes of the flat-field conditions on the reduced spectrum. The importance of every flat-field matrix component is tested and discussed and the noise propagation through data reduction is analyzed. It is documented that the errors of the basic spectral line characteristics, continuum intensity, line centre intensity and full width at the half maxima of the line have variations between 0.5% and 15% and the errors of the line centre Doppler velocity and bisectors fluctuate by up to 200 m s-1, if derived from imprecise reductions, compared to precise ones.

The diversity of SCUBA-selected galaxies

We present extensive observations of a sample of distant, submillimetre (submm) galaxies detected in the field of the massive cluster lens, Abell1835, using the Submm Common-User Bolometer Array (SCUBA). Taken in conjunction with earlier observations of other submm-selected sources (Ivison et al. 1998; Smail et al. 1999; Soucail et al. 1999) we now have detailed, multi-wavelength observations of seven examples of the submm population, having exploited the combination of achromatic amplification by cluster lenses and lavish archival datasets. These sources, all clearly at z > 1, illustrate the wide range in the radio and optical properties of distant submm-selected galaxies. We include detailed observations of the first candidate ‘pure’ starburst submm galaxy at high redshift, a z = 2.56 interacting galaxy which shows no obvious sign of hosting an AGN. The remaining sources have varying degrees of inferred AGN activity (three from seven of the most luminous show some evidence of the presence of an AGN) although even when an AGN is obviously present it is still not apparent if reprocessed radiation from this source dominates the submm emission. In contrast with the variation in the spectral properties, we see relatively homogeneous morphologies for the population, with a large fraction of merging or interacting systems. Our study shows that virtually identical spectral energy distributions are seen for galaxies which exhibit strikingly different optical/UV spectral-line characteristics. We conclude that standard optical/UV spectral classifications are misleading when applied to distant, highly obscured galaxies and that we must seek other means of determining the various contributions to the overall energy budget of submm galaxies and hence to the far-infrared extragalactic background.

Local vibrations in systems of interacting adsorbed molecules

A lattice system of adsorbed molecules is treated that is characterized by two bands of vibrational excitations. The first one originates from the collectivization of local high-frequency vibrations of individual molecules, which results from lateral intermolecular interactions. The second one arises due to the analogous collectivization of low-frequency resonance molecular modes, with their lifetimes governed by the coupling with substrate phonons. The temperature dependence of the spectral line shape for local vibrations is analyzed in the model that includes all kinds of cubic and quartic anharmonic coupling between high-frequency and low-frequency molecular modes in the fourth-order perturbation theory for the two-time retarded Green’s functions in the coordinate-momentum representation. As shown, various processes that involve four vibrational excitations and contribute to the line broadening for local vibrations are dominated by quartic anharmonic coefficients renormalized in terms of the cubic one; the renormalization is caused by the effective anharmonic force acting on each harmonic oscillator. Based on the translation symmetry of the system in surface-parallel directions, the quasimode approximation is substantiated, which enables the spectral line shift and width for local vibrations to be expressed in terms of dispersion laws and lifetimes for low-frequency molecular modes. The results obtained permit spectral line characteristics of local vibrations to be estimated for H/Si(111) and H(D)/C(111) in nice accordance with the experimentally measured values. Lateral interactions of low-frequency modes are shown to result in their shorter lifetimes and hence in the additionally narrowed spectral lines. The contribution from lateral interactions of local vibrations proves to be significant for systems with the sufficiently wide local vibration band and low frequencies of resonance modes, as, for instance, in OH/SiO2 and 2×1 phase of CO/NaCl(100).