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This paper discusses some features of the spectral line profile theory used in the treatment of measured atomic transitions. It is shown that going beyond the established linear approximation for the spectral line contour in the case of its nonresonant extension, the potential for a more accurate extraction of atomic characteristics from experimental data arises. Using the example of the Lyman- α (Ly α ) transition in hydrogen, a simple analysis of the observed spectral line distorted by a possible interfering transitions is given. In particular, the results obtained in the present work clearly demonstrate that the processing of the same experimental data at different settings can provide an accurate determination of the transition frequency, the centre of gravity as well as the hyperfine splitting of the ground state in hydrogen-like atomic systems. The latter is especially important for setting up precision spectroscopic experiments on the antihydrogen atom. [ABSTRACT FROM AUTHOR]

This work reviews the numerical simulation of resonance radiation transfer in gaseous media with 3D geometry and under the conditions of nonstationary excitation and ionization kinetics. The rate balance equations for population densities of a multilevel atom are determined by direct and inverse collisional-radiative processes. At the same time, the probabilities of stimulated photoexcitation processes at any point of the gaseous medium depend on the radiation intensity averaged over solid angles and frequency. This average intensity is the sum of the external radiation intensity (which propagates through the medium and is absorbed by the atoms) and its own radiation formed by internal sources of photons. The mathematical formulation of the problem of collisional-radiative kinetics is given by a system of integro-differential equations. To calculate a triple integral over the frequency and angle variables, we apply discrete-difference methods, i.e., the method of discretization of the volume on impact planes. With developed unique techniques, methods, and computational algorithms, the Cauchy problem for a system of integro-differential equations is reduced to a system of ordinary differential equations, which is then solves numerically using the Adams and Gear methods. We provide the results for applying modeling in a certain class of problems of photoexitation and luminescence kinetics of gases under the action by external radiation. The research performed complements the astrophysical theory of radiative transfer and also makes a significant contribution to the development of spectroscopic methods for diagnosing radiating gases and plasmas. [ABSTRACT FROM AUTHOR]

The effect of two factors, i.e., the dependence of the broadening coefficients γ and shifting coefficient δ on the speed of absorbing water vapor molecule (wind effect) and a change in the H2O molecule speed upon collision with gas atoms, on the profile of an absorption line of water vapor in a mixture with helium, argon, krypton, and xenon is studied with three absorption lines of H2O molecule from ν1 + ν2 + ν3 band with different rotational quantum numbers of the initial quantum state. The wind effect is shown to be the strongest in interactions of H2O molecules with argon, krypton, and xenon atoms. The results can be used in the analysis of absorption spectra of water vapor mixed with monatomic gases. [ABSTRACT FROM AUTHOR]

In order to investigate the time variations and the peculiarities of the optical spectra of the RV Tauri star R Sct, high-resolution spectroscopic observations in the wavelength interval around the line (6540–6580 Å) were obtained between 2014 and 2018. The phase dependence of the equivalent widths and radial velocities was measured for the and Fe I 5669.224 Å lines, respectively. shows considerable changes in its line profile. We observed double-peaked emission and an inverse P Cygni profile in this line. We detected a variation from inverse P Cygni to P Cygni profile for both Ti I 6554.239 Å and Ca I 6572.797 Å lines at phases where the shock wave is propagating through the atmospheric layer in which the Hα lines are forming, particularly around which is just after the deep minimum and , just after shallow minimum. An increase in the shock wave velocity generates a decrease in the intensity, which is explained by the ionization phenomenon. The detailed description of the variations in R Sct reveals its important properties. The observation of the P Cygni and the inverse P Cygni profile indicate that expanding and infalling layers are simultaneously present in the stellar atmosphere, pointing out the complicated nature of this object. [ABSTRACT FROM AUTHOR]

We analytically obtained the frequency dependences of the absorption coefficient profile, taking into account the combined influence of the macroscopic motion of matter, Doppler and Voigt mechanisms of spectral line broadening. The effect of rotation of a spherical plasma on the formation of resonant fluorescence by barium ions upon absorption of laser radiation at a wavelength of 455.4 nm was studied. The deformation of the frequency shape of the laser radiation passing through the plasma and the emission spectrum is due to a shift in the absorption coefficient profile and its broadening caused by the rotational motion of the plasma. An increase in the resonant photons escape from the medium stipulated by the broadening of the emission spectrum of the resonance line is predicted. [ABSTRACT FROM AUTHOR]

This paper shows extensive employment of animations as a response to the needs of the GPS implementation facilitation. The general architecture of the developed application that helps to understand how the geometrical tolerances shall be applied and what are their functional aims is shortly presented. This paper is focused on the line profile and the surface profile tolerances that are more precisely defined due to set of rules given in recently published standard ISO 1660:2017. The paper contains a few screenshots of the interactive animated sequences that demonstrate two alternative possibilities of bended round bar tolerancing as well as shows appropriate verification methods. The experience gathered during university lectures and a number of vocational trainings confirms the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

We have investigated the intensities and full width at half maximum (FWHM) of the high dispersion spectroscopic N III emission lines of AG Peg, observed with the Hamilton Echelle Spectrograph (HES) in three different epochs at Mt. Hamilton’s Lick Observatory. The earlier theoretical Bowen line study assumed the continuum fluorescence effect, presenting a large discrepancy with the present data. Hence, we analyzed the observed N III lines assuming line fluorescence as the only suitable source: (1) The O III and N III resonance line profiles near λ 374 were decomposed, using the Gaussian function, and the contributions from various O III line components were determined. (2) Based on the theoretical resonant N III intensities, the expected N III Bowen intensities were obtained to fit the observed values. Our study shows that the incoming line photon number ratio must be considered to balance at each N III Bowen line level in the ultraviolet radiation according to the observed lines in the optical zone. We also found that the average FWHM of the N III Bowen lines was about 5 km·s-1 greater than that of the O III Bowen lines, perhaps due to the inherently different kinematic characteristics of their emission zones.

• The CRDS spectrum of pure and air-broadened water vapor is recorded between 6071.4 and 6080.0 cm−1. • The targeted spectral region is that selected by the MERLIN mission for atmospheric CH 4 retrieval. • Uncertainty on the interfering water lines may affect the obtained atmospheric methane columns. • Line parameters are determined from multi-spectrum fits of spectra recorded at different pressures. • The speed dependent Nelkin-Ghatak and Nelkin-Ghatak profile are used to model the line shape and a recommended line list is provided. The MERLIN mission (MEthane Remote LIdar missioN) is a space mission dedicated to the methane atmospheric retrieval based on absorption LIDAR measurements at nadir. The methane columns will be obtained by difference between the LIDAR signal at the on-line wavelength corresponding to the R (6) manifold of the 2ν 3 band of methane at 6077 cm−1 and the off-line signal at a wavenumber about 1 cm−1 below. As atmospheric water vapor lines may affect the methane retrievals, the present study is dedicated to a detailed laboratory characterization of the interfering water vapor absorption in the targeted region. To this aim, high sensitivity absorption spectra of pure water vapor and water vapor in air are recorded at room temperature using a cavity ring down spectrometer (CRDS) combined with a self-referenced frequency comb. The CRDS recordings cover the 6071.4–6080.0 cm−1 interval with a noise equivalent absorption, α min , on the order of 5 × 10−11 cm−1 for a 10−3 cm−1 sampling of the spectra. The measured pure and air-broadened spectra are analyzed using the Nelkin-Ghatak (NG) or the speed-dependent Nelkin-Ghatak (sdNG) profile. A multi-spectrum fitting procedure in which series of spectra recorded at different pressures (between 0.7 and 12 Torr for pure water vapor and between 100 and 700 Torr for H 2 O in air) are simultaneously adjusted, is used to retrieve the spectroscopic parameters. Accurate line parameters including self- and air-pressure shifts, self- and air-broadenings, Dicke narrowing and the speed-dependent coefficients are determined for most of the lines with intensity larger than 10−28 cm/molecule at 296 K. The list is complemented with literature data (in particular from the HITRAN database) to be complete down to a 10−29 cm/molecule intensity cut-off. The obtained spectroscopic results are discussed in comparison with literature data. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The qualitative and quantitative effects on the line profile of hard and soft velocity-changing large- and small-angle scattering collisions of absorbing molecules, respectively, are considered. It is shown that large-angle scattering significantly contributes to the diffusion profile model, known as the "soft" collision model, as compared to that in the hard collision model. The difference between these traditional models lies only in the mathematical representation of the collision integral, either in integral or differential form, and the following analytical expressions for the profiles. Simple approximate formulas for the profile are derived and tested, which simultaneously take into account hard and soft collisions. [ABSTRACT FROM AUTHOR]

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We present an accurate digital surface model (DSM) derived from high-resolution Pleiades-1B 0.5 m panchromatic tri-stereo images, covering an area of 400 km2 over the Athens Metropolitan Area. Remote sensing and photogrammetry tools were applied, resulting in a 1 m X 1 m posting DSM over the study area. The accuracy of the produced DSM was evaluated against measured elevations by a differential Global Positioning System (d-GPS) and a reference DSM provided by the National Cadaster and Mapping Agency S.A. Different combinations of stereo and tri-stereo images were used and tested on the quality of the produced DSM. Results revealed that the DSM produced by the tri-stereo analysis has a root mean square error (RMSE) of 1.17 m in elevation, which lies within the best reported in the literature. On the other hand, DSMs derived by standard analysis of stereo-pairs from the same sensor were found to perform worse. Line profile data showed similar patterns between the reference and produced DSM. Pleiades tri-stereo high-quality DSM products have the necessary accuracy to support applications in the domains of urban planning, including climate change mitigation and adaptation, hydrological modelling and natural hazards, being an important input for simulation models and morphological analysis at local scales. [ABSTRACT FROM AUTHOR]