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Articoli di riviste sul tema "Spectral line formation Congresses"

Autore: Grafiati

Pubblicato: 29 luglio 2024

Ultima modifica: 30 luglio 2024

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1

Paletou, F., e C. Peymirat. "Full non–LTE spectral line formation". Astronomy & Astrophysics 649 (maggio 2021): A165. http://dx.doi.org/10.1051/0004-6361/202040005.

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Radiative transfer out of local thermodynamic equilibrium (NLTE) has been increasingly adressed, mostly numerically, for about six decades now. However, the standard NLTE problem most often refers to the only deviation of the distribution of photons from their equilibrium, that is to say a Planckian distribution. Hereafter we revisit after Oxenius (1986, Kinetic theory of particles and Photons – Theoretical Foundations of non–LTE Plasma Spectroscopy, Springer) the so-called full NLTE problem, which considers coupling and therefore solving self–consistently for deviations from equilibrium distributions of photons as well as for massive particles constituting the atmospheric plasma.

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2

Oxenius, J., e E. Simonneau. "Kinetic Theory of Spectral Line Formation". Annals of Physics 234, n. 1 (agosto 1994): 60–101. http://dx.doi.org/10.1006/aphy.1994.1074.

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3

Klevas, J., A. Kučinskas, M. Steffen, E. Caffau e H. G. Ludwig. "Lithium spectral line formation in stellar atmospheres". Astronomy & Astrophysics 586 (febbraio 2016): A156. http://dx.doi.org/10.1051/0004-6361/201526403.

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4

Peraiah, A., e M. Srinivasa Rao. "Compton broadening effect on spectral line formation". Astrophysics and Space Science 343, n. 1 (18 settembre 2012): 195–211. http://dx.doi.org/10.1007/s10509-012-1233-0.

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5

Nikoghossian, A. G. "Spectral line formation in a mesoturbulent atmosphere". Astrophysics 50, n. 2 (aprile 2007): 175–86. http://dx.doi.org/10.1007/s10511-007-0017-7.

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6

Grec, C., H. Uitenbroek, M. Faurobert e C. Aime. "Measuring line formation depths by cross-spectral analysis". Astronomy and Astrophysics 514 (maggio 2010): A91. http://dx.doi.org/10.1051/0004-6361/200811455.

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7

Letunov, Andrey Yu, e Valery S. Lisitsa. "Review of Rydberg Spectral Line Formation in Plasmas". Atoms 11, n. 10 (17 ottobre 2023): 133. http://dx.doi.org/10.3390/atoms11100133.

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The present review is dedicated to the problem of an array of transitions between highly-excited atomic levels. Hydrogen atoms and hydrogen-like ions in plasmas are considered here. The presented methods focus on calculation of spectral line shapes. Fast and simple methods of universal ionic profile calculation for the Hnα (Δn=1) and Hnβ (Δn=2) spectral lines are demonstrated. The universal dipole matrix elements formulas for the Hnα and Hnβ transitions are presented. A fast method for spectral line shape calculations in the presence of an external magnetic field using the formulas for universal dipole matrix elements is proposed. This approach accounts for the Doppler and Stark–Zeeman broadening mechanisms. Ion dynamics effects are treated via the frequency fluctuation model. The accuracy of the presented model is discussed. A comparison of this approach with experimental data and the results of molecular dynamics simulation is demonstrated. The kinetics equation for the populations of highly-excited ionic states is solved in the parabolic representation. The population source associated with dielectronic recombination is considered.

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8

Albrow, Michael D., e P. L. Cottrell. "Formation Depths of Spectral Lines in Cepheids". International Astronomical Union Colloquium 155 (1995): 373–74. http://dx.doi.org/10.1017/s0252921100037568.

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There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.

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9

Dravins, Dainis. "Observed and computed spectral line profiles". Symposium - International Astronomical Union 176 (1996): 519–22. http://dx.doi.org/10.1017/s0074180900083534.

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For the diagnostics of stellar surface structure, studies of “ordinary” line profiles may prove inadequate. However, hydrodynamic models may be constrained by second-order quantities, such as line asymmetries and wavelength shifts (and especially the differential behavior between lines of different excitation potential, ionization stage, and height of formation, as well as by the time dependence).

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10

Ivonina, Liudmila. "The Triumph of Peace: International Congresses and European Society in the Time of Courts and Alliances". ISTORIYA 13, n. 1 (111) (2022): 0. http://dx.doi.org/10.18254/s207987840018801-0.

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The formation of the first state system in Europe took place from the conclusion of the Peace of Westphalia in 1648, as a result of the Thirty Years' War (1618-1648), to the Utrecht (1713) and Rastatt-Baden (1714) Congresses which finished the end of the war of the Spanish Succession. The legal fixation of the Westphallian system was accompanied by its public perception and acceptance. First of all, this was demonstrated by International Congresses, which were not only a common negotiation process, but also a place of representation of the significance and culture of each state. In fact, the European Congress was a carefully designed triumph of peace within the continent, which required considerable funds, was widely covered in the press and glorified in celebrations, paintings, the release of commemorative medals, poetry and even fashion. The article presents the most striking examples of the analysis of the representation forms of Peace Congresses. The author believes that negotiations between states and the conclusion of peace made a significant contribution to the civilization heritage of Europe. The factor of transition from war to peace was the strongest stimulus for the transformation of the government structure in line with the monopolization of power, the development of trade, the banking system, productive forces and culture, which changed people's attitude to their own personality and environment. The publicity of International Congresses can also be considered as incentive for the development of the Law of Nations and as an act of humanitarian diplomacy. Peace Congresses were designed to minimize the heavy legacy of military conflicts in the historical memory.

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11

Collet, R., M. Asplund e F. Thévenin. "Effects of line-blocking on the non-LTE Fe I spectral line formation". Astronomy & Astrophysics 442, n. 2 (7 ottobre 2005): 643–50. http://dx.doi.org/10.1051/0004-6361:20053363.

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12

Kravchenko, K., S. Van Eck, A. Chiavassa, A. Jorissen, B. Freytag e B. Plez. "Tomography of cool giant and supergiant star atmospheres". Astronomy & Astrophysics 610 (febbraio 2018): A29. http://dx.doi.org/10.1051/0004-6361/201731530.

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Context. Cool giant and supergiant star atmospheres are characterized by complex velocity fields originating from convection and pulsation processes which are not fully understood yet. The velocity fields impact the formation of spectral lines, which thus contain information on the dynamics of stellar atmospheres. Aim. The tomographic method allows to recover the distribution of the component of the velocity field projected on the line of sight at different optical depths in the stellar atmosphere. The computation of the contribution function to the line depression aims at correctly identifying the depth of formation of spectral lines in order to construct numerical masks probing spectral lines forming at different optical depths. Methods. The tomographic method is applied to one-dimensional (1D) model atmospheres and to a realistic three-dimensional (3D) radiative hydrodynamics simulation performed with CO5BOLD in order to compare their spectral line formation depths and velocity fields. Results. In 1D model atmospheres, each spectral line forms in a restricted range of optical depths. On the other hand, in 3D simulations, the line formation depths are spread in the atmosphere mainly because of temperature and density inhomogeneities. Comparison of cross-correlation function profiles obtained from 3D synthetic spectra with velocities from the 3D simulation shows that the tomographic method correctly recovers the distribution of the velocity component projected on the line of sight in the atmosphere.

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13

Drew, J. E. "On spectral line formation in winds from extended continuum sources". Monthly Notices of the Royal Astronomical Society 218, n. 1 (1 gennaio 1986): 41P—47P. http://dx.doi.org/10.1093/mnras/218.1.41p.

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14

Rosato, J. "Spectral line formation with wave effects in optically thick plasmas". Journal of Physics: Conference Series 397 (6 dicembre 2012): 012018. http://dx.doi.org/10.1088/1742-6596/397/1/012018.

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15

Fabbian, D., M. Asplund, M. Carlsson e D. Kiselman. "CI non–LTE spectral line formation in late-type stars". Proceedings of the International Astronomical Union 1, S228 (maggio 2005): 255–56. http://dx.doi.org/10.1017/s1743921305005703.

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16

Israelian, G. "The effect of continuum scattering processes on spectral line formation". Journal of Quantitative Spectroscopy and Radiative Transfer 67, n. 4 (novembre 2000): 293–301. http://dx.doi.org/10.1016/s0022-4073(99)00238-1.

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17

Amarsi, A. M. "On line contribution functions and examining spectral line formation in 3D model stellar atmospheres". Monthly Notices of the Royal Astronomical Society 452, n. 2 (15 luglio 2015): 1612–16. http://dx.doi.org/10.1093/mnras/stv1392.

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18

Tichý, A., J. Štěpán, J. Trujillo Bueno e J. Kubát. "Formation of polarized spectral lines in atmospheres with horizontal inhomogeneities". Proceedings of the International Astronomical Union 10, S305 (dicembre 2014): 401–6. http://dx.doi.org/10.1017/s1743921315005128.

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AbstractWe study the problem of the generation and transfer of spectral line intensity and polarization in models of stellar atmospheres with horizontal plasma inhomogeneities. We solve the non-LTE radiative transfer problem in full 3D geometry taking into account resonant scattering polarization and its modification by magnetic fields via the Hanle effect. We show that horizontal fluctuations of the thermodynamical conditions of stellar atmospheres can have a significant impact on the linear polarization of the emergent spectral line radiation and its center-to-limb variation.

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19

Hayek, W., M. Asplund, R. Collet e Å. Nordlund. "3D LTE spectral line formation with scattering in red giant stars". Astronomy & Astrophysics 529 (22 aprile 2011): A158. http://dx.doi.org/10.1051/0004-6361/201015782.

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20

Rangarajan, K. E., D. Mohan Rao e A. Peraiah. "The effects of non-coherent electron scattering on spectral line formation". Monthly Notices of the Royal Astronomical Society 250, n. 3 (1 giugno 1991): 633–37. http://dx.doi.org/10.1093/mnras/250.3.633.

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21

Wang, Ella Xi, Thomas Nordlander, Martin Asplund, Anish M. Amarsi, Karin Lind e Yixiao Zhou. "3D NLTE spectral line formation of lithium in late-type stars". Monthly Notices of the Royal Astronomical Society 500, n. 2 (31 ottobre 2020): 2159–76. http://dx.doi.org/10.1093/mnras/staa3381.

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ABSTRACT Accurately known stellar lithium abundances may be used to shed light on a variety of astrophysical phenomena such as big bang nucleosynthesis, radial migration, ages of stars and stellar clusters, and planet engulfment events. We present a grid of synthetic lithium spectra that are computed in non-local thermodynamic equilibrium (NLTE) across the stagger grid of three-dimensional (3D) hydrodynamic stellar atmosphere models. This grid covers three Li lines at 610.4, 670.8, and 812.6 nm for stellar parameters representative of FGK-type dwarfs and giants, spanning Teff = 4000–7000 K, log g = 1.5–5.0, $[\rm {Fe}/\rm {H}]= -4.0$–0.5, and A(Li) = −0.5–4.0. We find that our abundance corrections are up to 0.15 dex more negative than in previous work, due to a previously overlooked NLTE effect of blocking of UV lithium lines by background opacities, which has important implications for a wide range of science cases. We derive a new 3D NLTE solar abundance of A(Li) = 0.96 ± 0.05, which is 0.09 dex lower than the commonly used value. We make our grids of synthetic spectra and abundance corrections publicly available through the breidablik package. This package includes methods for accurately interpolating our grid to arbitrary stellar parameters through methods based on Kriging (Gaussian process regression) for line profiles, and multilayer perceptrons (a class of fully connected feedforward neural networks) for NLTE corrections and 3D NLTE abundances from equivalent widths, achieving interpolation errors of the order of 0.01 dex.

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22

Barichello, L. B., e C. E. Siewert. "The FN method for spectral-line formation by completely noncoherent scattering". Journal of Quantitative Spectroscopy and Radiative Transfer 60, n. 2 (agosto 1998): 261–76. http://dx.doi.org/10.1016/s0022-4073(97)00171-4.

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23

Lisitsa, Valery, Mikhail Kadomtsev, Vladislav Kotov, Vladislav Neverov e Vladimir Shurygin. "Hydrogen Spectral Line Shape Formation in the SOL of Fusion Reactor Plasmas". Atoms 2, n. 2 (15 maggio 2014): 195–206. http://dx.doi.org/10.3390/atoms2020195.

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24

Sabbey, C. N., D. D. Sasselov, M. S. Fieldus, J. B. Lester, K. A. Venn e R. P. Butler. "On Spectral Line Formation and Measurement in Cepheids: Implications to Distance Determination". Astrophysical Journal 446 (giugno 1995): 250. http://dx.doi.org/10.1086/175783.

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25

Sapar, A., e L. Sapar. "Formation of resonance spectral line profiles in stellar wind: Theory and observations". Astronomical & Astrophysical Transactions 18, n. 3 (dicembre 1999): 475–85. http://dx.doi.org/10.1080/10556799908203004.

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26

Kosarev, N. I. "Formation of the contour of a spectral line upon partial frequency redistribution". Optics and Spectroscopy 102, n. 1 (gennaio 2007): 8–14. http://dx.doi.org/10.1134/s0030400x0701002x.

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27

Antia, H. M. "A Model for Stellar Convection and Spectral Line Asymmetries". Symposium - International Astronomical Union 138 (1990): 417–20. http://dx.doi.org/10.1017/s0074180900044417.

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A model for stellar convection zones based on linear convective modes using a nonlocal mixing length theory is developed to study the spectral line asymmetries and the line shifts resulting from convective motions in the stellar photospheric region. The amplitudes of these linear convective modes is estimated by requiring the convective flux due to a linear superposition of such modes to reproduce the convective flux in the mixing length model. To study the spectral line asymmetries the convective mode with the largest amplitude in the photospheric line formation region is chosen to represent the stellar velocity field and the accompanying intensity fluctuations. Synthetic spectral line profiles are obtained by summing locally symmetric profiles over the stellar disk according to the local Doppler velocity and intensity fluctuations. The resulting line bisector shapes and the line shifts are compared with observations for α-Cen B. It is found that while the simple model proposed here can explain either the line shifts or the line bisector shape reasonably well, it fails to explain both these characteristics simultaneously.

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28

Torres-Papaqui, J. P., R. Coziol e R. A. Ortega-Minakata. "The Chemical Evolution of Narrow Emission Line Galaxies: the Key to their Formation Processes". Acta Universitaria 21 (1 settembre 2011): 82–91. http://dx.doi.org/10.15174/au.2011.39.

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Using the largest sample of narrow emission line galaxies available so far, we show that their spectral characteristics are correlated with different physical parameters, like the chemical abundances, the morphologies, the masses of the bulge and the mean stellar age of the stellar populations of the host galaxies. It suggests that the spectral variations observed in standard spectroscopic diagnostic diagrams are not due solely to variations of ionization parameters or structures but reflect also the chemical evolution of the galaxies, which in turn can be explained by different galaxy formation processes.

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29

Kubát, Jiří, Jiří Krtička, Izold B. Pustylnik e Viktor Votruba. "The Possibility of a Disk Formation around Late B Stars". Symposium - International Astronomical Union 215 (2004): 49–50. http://dx.doi.org/10.1017/s007418090019518x.

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Line driven wind in late B stars causes significant heating of layers just above the photosphere. This large heating is a source of a thermal wind, which together with fast rotation opens the possibility of a formation of a disk. We refer to such disk as to a radiation induced disk. Disk inhibition by nonradial line force has only little effect in this case, since absorption in spectral lines is not the main wind driving mechanism.

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30

Steinbach, Julia C., Markus Schneider, Otto Hauler, Günter Lorenz, Karsten Rebner e Andreas Kandelbauer. "A Process Analytical Concept for In-Line FTIR Monitoring of Polysiloxane Formation". Polymers 12, n. 11 (25 ottobre 2020): 2473. http://dx.doi.org/10.3390/polym12112473.

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The chemical synthesis of polysiloxanes from monomeric starting materials involves a series of hydrolysis, condensation and modification reactions with complex monomeric and oligomeric reaction mixtures. Real-time monitoring and precise process control of the synthesis process is of great importance to ensure reproducible intermediates and products and can readily be performed by optical spectroscopy. In chemical reactions involving rapid and simultaneous functional group transformations and complex reaction mixtures, however, the spectroscopic signals are often ambiguous due to overlapping bands, shifting peaks and changing baselines. The univariate analysis of individual absorbance signals is hence often only of limited use. In contrast, batch modelling based on the multivariate analysis of the time course of principal components (PCs) derived from the reaction spectra provides a more efficient tool for real-time monitoring. In batch modelling, not only single absorbance bands are used but information over a broad range of wavelengths is extracted from the evolving spectral fingerprints and used for analysis. Thereby, process control can be based on numerous chemical and morphological changes taking place during synthesis. “Bad” (or abnormal) batches can quickly be distinguished from “normal” ones by comparing the respective reaction trajectories in real time. In this work, FTIR spectroscopy was combined with multivariate data analysis for the in-line process characterization and batch modelling of polysiloxane formation. The synthesis was conducted under different starting conditions using various reactant concentrations. The complex spectral information was evaluated using chemometrics (principal component analysis, PCA). Specific spectral features at different stages of the reaction were assigned to the corresponding reaction steps. Reaction trajectories were derived based on batch modelling using a wide range of wavelengths. Subsequently, complexity was reduced again to the most relevant absorbance signals in order to derive a concept for a low-cost process spectroscopic set-up which could be used for real-time process monitoring and reaction control.

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Medvid', Artur, Pavels Onufrijevs, Edvins Dauksta e Volodymyr Kyslyi. "“Black Silicon” Formation by Nd:YAG Laser Radiation". Advanced Materials Research 222 (aprile 2011): 44–47. http://dx.doi.org/10.4028/www.scientific.net/amr.222.44.

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The possibility to form “black silicon” on the surface of Si structure by Nd:YAG laser radiation has been shown. The shape and height of micro-cone structure strongly depends on Nd:YAG laser intensity and number of laser pulses. Light is repeatedly reflected between the cones in the way that most of it is absorbed. Si micro-cone structure spectral thermal radiation is close to black body spectral radiance, which makes this structure useful for solar cells application. The micro-chemical analysis performed by SEM has shown that the microstructures contain NiSi2. This was approved by presence of LO phonon line in Raman back scattering spectrum. The control of micro-cone shape and height was achieved by changing the laser intensity and number of pulses.

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Evans, Neal J., Lee G. Mundy, John H. Davis e Paul Vanden Bout. "Sub-Millimeter Spectral Line Observations in Very Dense Regions". Symposium - International Astronomical Union 115 (1987): 173. http://dx.doi.org/10.1017/s0074180900095322.

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In a search for very high density (n ≳ 107 cm−3) regions, the Millimeter Wave Observatory 5-m telescope was used to observe several submillimeter lines. The regions studied were Orion A, M17, S140, and NGC2024. The lines were CS(J=7-6), H2CO(JK-1K1=515→414), and HCN(J=4-3). These data are combined with data at millimeter wavelengths to derive the volume density and the results are compared to those deduced from millimeter lines alone (Snell et al. 1984). In NGC2024, higher densities (≳ 107 cm−3) are clearly indicated by the sub-mm lines than were derived by Snell et al. In M17, derived densities are also higher, but uncertainties overlap the Snell et al. solutions. The range of densities derived from CS and HCN are consistent. The sub-millimeter lines of these species appear to be good probes of the highest densities present in regions of active star formation.

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Štěpán, J. "Three-dimensional simulations of scattering polarization and the Hanle effect in MHD chromospheric models". Proceedings of the International Astronomical Union 10, S305 (dicembre 2014): 360–67. http://dx.doi.org/10.1017/s1743921315005050.

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AbstractScattering line polarization and the Hanle effect are among the most important mechanisms for diagnostics of the solar and stellar atmospheres. The fact that real stellar atmospheres are horizontally inhomogeneous makes the spectral synthesis and interpretation very challenging because the effect of thermodynamic fluctuations on spectral line polarization is entangled with the action of magnetic fields. This applies to the spatially resolved as well as to the averaged spectra. The necessary step towards the interpretation of such spectra is to study the line formation in sufficiently realistic 3D MHD models and compare the synthetic spectra with observations. This paper gives an overview of recent progress in the field of 3D NLTE synthesis of polarized spectral lines resulting from investigations with the radiative transfer code PORTA.

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Roth, M., A. Herrero, R. H. Mendez, R. P. Kudritzki, K. Butler e H. G. Groth. "The Metal-Line Spectra of Central Stars of Planetary Nebulae". Symposium - International Astronomical Union 131 (1989): 317. http://dx.doi.org/10.1017/s0074180900138653.

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We present spectral descriptions based on high-resolution spectrograms of central stars of planetary nebulae, obtained with the ESO 3,6-m telescope + CASPEC (Cassegrain Echelle Spectrograph). We make preliminary determinations of stellar photospheric metal abundances, using non-LTE model atmospheres and non-LTE line formation calculations.

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Beuther, H., J. C. Mottram, A. Ahmadi, F. Bosco, H. Linz, Th Henning, P. Klaassen et al. "Fragmentation and disk formation during high-mass star formation". Astronomy & Astrophysics 617 (settembre 2018): A100. http://dx.doi.org/10.1051/0004-6361/201833021.

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Context. High-mass stars form in clusters, but neither the early fragmentation processes nor the detailed physical processes leading to the most massive stars are well understood. Aims. We aim to understand the fragmentation, as well as the disk formation, outflow generation, and chemical processes during high-mass star formation on spatial scales of individual cores. Methods. Using the IRAM Northern Extended Millimeter Array (NOEMA) in combination with the 30 m telescope, we have observed in the IRAM large program CORE the 1.37 mm continuum and spectral line emission at high angular resolution (~0.4″) for a sample of 20 well-known high-mass star-forming regions with distances below 5.5 kpc and luminosities larger than 104 L⊙. Results. We present the overall survey scope, the selected sample, the observational setup, and the main goals of CORE. Scientifically, we concentrated on the mm continuum emission on scales on the order of 1000 AU. We detect strong mm continuum emission from all regions, mostly due to the emission from cold dust. The fragmentation properties of the sample are diverse. We see extremes where some regions are dominated by a single high-mass core whereas others fragment into as many as 20 cores. A minimum-spanning-tree analysis finds fragmentation at scales on the order of the thermal Jeans length or smaller suggesting that turbulent fragmentation is less important than thermal gravitational fragmentation. The diversity of highly fragmented vs. singular regions can be explained by varying initial density structures and/or different initial magnetic field strengths. Conclusions. A large sample of high-mass star-forming regions at high spatial resolution allows us to study the fragmentation properties of young cluster-forming regions. The smallest observed separations between cores are found around the angular resolution limit which indicates that further fragmentation likely takes place on even smaller spatial scales. The CORE project with its numerous spectral line detections will address a diverse set of important physical and chemical questions in the field of high-mass star formation.

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Frémat, Y., J. Zorec, A. M. Hubert, M. Floquet, N. Leister, R. Levenhagen, J. Chauville e D. Ballereau. "Fast Rotating Stars: Effect of the Aspect Angle on Line Profiles". Symposium - International Astronomical Union 215 (2004): 23–24. http://dx.doi.org/10.1017/s0074180900195117.

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Fast rotation is expected to flatten the star and to produce non uniform temperature and density distributions (i.e. gravitational darkening). While the flattening mostly increases the absolute flux level of the energy distribution, gravitational darkening makes an equator-on star apparently cooler than a star seen through the pole. Both effects (Collins et al. 1991) influence the colours and the location of the star in the HR diagram but also, in a more subtle way, its spectral line profiles. More particularly, in early B type stars, gravitational darkening tends to privilege at the poles the formation of the ions with the highest ionization potentials and directly affects line formation. Consequently, most spectral line shapes - and especially the weakest ones - become aspect angle dependent which in several cases may play a role in the fundamental parameter determination procedures or even in the determination of stellar chemical abundances.

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Koribalski, B. S. "Overview on Spectral Line Source Finding and Visualisation". Publications of the Astronomical Society of Australia 29, n. 3 (2012): 359–70. http://dx.doi.org/10.1071/as12030.

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AbstractHere I will outline successes and challenges for finding spectral line sources in large data cubes that are dominated by noise. This is a 3D challenge as the sources we wish to catalog are spread over several spatial pixels and spectral channels. While 2D searches can be applied, e.g. channel by channel, optimal searches take into account the 3-dimensional nature of the sources. In this overview I will focus on Hi 21-cm spectral line source detection in extragalactic surveys, in particular HIPASS, the Hi Parkes All-Sky Survey and WALLABY, the ASKAP Hi All-Sky Survey. I use the original HIPASS data to highlight the diversity of spectral signatures of galaxies and gaseous clouds, both in emission and absorption. Among others, I report the discovery of a 680 km s−1 wide Hi absorption trough in the megamaser galaxy NGC 5793. Issues such as source confusion and baseline ripples, typically encountered in single-dish Hi surveys, are much reduced in interferometric Hi surveys. Several large Hi emission and absorption surveys are planned for the Australian Square Kilometre Array Pathfinder (ASKAP): here we focus on WALLABY, the 21-cm survey of the sky (δ < + 30°; z < 0.26) which will take about one year of observing time with ASKAP. Novel phased array feeds (‘radio cameras’) will provide 30 deg2 instantaneous field-of-view. WALLABY is expected to detect more than 500 000 galaxies, unveil their large-scale structures and cosmological parameters, detect their extended, low-surface-brightness disks as well as gas streams and filaments between galaxies. It is a precursor for future Hi surveys with SKA Phase I and II, exploring galaxy formation and evolution. The compilation of highly reliable and complete source catalogs will require sophisticated source-finding algorithms as well as accurate source parametrisation.

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38

Marziani, Paola, Edi Bon, Natasa Bon, Ascension del Olmo, Mary Martínez-Aldama, Mauro D’Onofrio, Deborah Dultzin, C. Negrete e Giovanna Stirpe. "Quasars: From the Physics of Line Formation to Cosmology". Atoms 7, n. 1 (4 febbraio 2019): 18. http://dx.doi.org/10.3390/atoms7010018.

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Quasars accreting matter at very high rates (known as extreme Population A (xA) or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars can radiate at a stable, extreme luminosity-to-mass ratio. This in turn translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the main optical and UV spectral properties of extreme Population A quasars that make them easily identifiable in large spectroscopic surveys at low- ( z ≲ 1 ) and intermediate-z (2 ≲ z ≲ 2.6), and the physical conditions that are derived for the formation of their emission lines. Ultimately, the analysis supports the possibility of identifying a virial broadening estimator from low-ionization line widths, and the conceptual validity of the redshift-independent luminosity estimates based on virial broadening for a known luminosity-to-mass ratio.

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39

Toriumi, Shin, Vladimir S. Airapetian, Kosuke Namekata e Yuta Notsu. "Universal Scaling Laws for Solar and Stellar Atmospheric Heating: Catalog of Power-law Index between Solar Activity Proxies and Various Spectral Irradiances". Astrophysical Journal Supplement Series 262, n. 2 (30 settembre 2022): 46. http://dx.doi.org/10.3847/1538-4365/ac8b15.

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Abstract The formation of extremely hot outer atmospheres is one of the most prominent manifestations of magnetic activity common to late-type dwarf stars, including the Sun. It is widely believed that these atmospheric layers, the corona, transition region, and chromosphere, are heated by the dissipation of energy transported upwards from the stellar surface by the magnetic field. This is signified by the spectral line fluxes at various wavelengths, scaled with power-law relationships against the surface magnetic flux over a wide range of formation temperatures, which are universal to the Sun and Sunlike stars of different ages and activity levels. This study describes a catalog of power-law indices between solar activity proxies and various spectral line fluxes. Compared to previous studies, we expanded the number of proxies, which now includes the total magnetic flux, total sunspot number, total sunspot area, and the F10.7 cm radio flux, and further enhanced the number of spectral lines by a factor of 2. This provides the data to study in detail the flux–flux scaling laws from the regions specified by the temperatures of the corona (log(T/K) = 6–7) to those of the chromosphere (log(T/K) ∼ 4), as well as the reconstruction of various spectral line fluxes of the Sun in the past, F-, G-, and K-type dwarfs, and the modeled stars.

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40

Mordini, Sabrina, Luigi Spinoglio e Juan Antonio Fernández-Ontiveros. "Calibration of mid- to far-infrared spectral lines in galaxies". Astronomy & Astrophysics 653 (settembre 2021): A36. http://dx.doi.org/10.1051/0004-6361/202140696.

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Context. Mid- to far-infrared (IR) lines are suitable in the study of dust-obscured regions in galaxies because dust extinction strongly decreases with wavelength, and therefore IR spectroscopy allows us to explore the most hidden regions of galaxies, where heavily obscured star formation as well as accretion onto supermassive black holes at the nuclei of galaxies occur. This is mostly important for the so-called cosmic noon (i.e. at redshifts of 1 < z < 3), at which point most of the baryonic mass in galaxies has been assembled. Aims. Our goal is to provide reliable calibrations of the mid- to far-IR ionic fine-structure lines, the brightest H2 pure rotational lines, and the polycyclic aromatic hydrocarbon (PAH) features, which we used to analyse current and future observations in the mm-submm range from the ground, as well as mid-IR spectroscopy from the upcoming James Webb Space Telescope. Methods. We used three samples of galaxies observed in the local Universe: star-forming galaxies (SFGs, 196), active galactic nuclei (AGN; 90−150 for various observables), and low-metallicity dwarf galaxies (40). For each population, we derive different calibrations of the observed line luminosities versus the total IR luminosities. Results. Through the resulting calibrations, we derive spectroscopic measurements of the star formation rate (SFR) and of the black hole accretion rate (BHAR) in galaxies using mid- and far-IR fine-structure lines, H2 pure rotational lines and PAH features. In particular, we derive robust star formation tracers based on the following: the [CII]158 μm line; the sum of the two far-IR oxygen lines, the [OI]63 μm line, and the [OIII]88 μm line; a combination of the neon and sulfur mid-IR lines; the bright PAH features at 6.2 and 11.3 μm; as well as – for the first time – the H2 rotational lines at 9.7, 12.3, and 17 μm. We propose the [CII]158 μm line, the combination of the two neon lines ([NeII]12.8 μm and [NeIII]15.5 μm), and, for solar-like metallicity galaxies that may harbour an AGN, the PAH 11.3 μm feature as the best SFR tracers. On the other hand, a reliable measure of the BHAR can be obtained using the [OIV]25.9 μm and the [NeV]14.3 and 24.3 μm lines. For the most commonly observed fine-structure lines in the far-IR, we compare our calibration with the existing ALMA observations of high-redshift galaxies. We find an overall good agreement for the [CII]158 μm line for both AGN and SFGs, while the [OIII]88 μm line in high-z galaxies is in better agreement with the low-metallicity local galaxies (dwarf galaxy sample) than with the SFGs, suggesting that high-z galaxies might have strong radiation fields due to low metal abundances, as expected.

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41

Dionatos, Odysseas, Tom Ray e Manuel Güdel. "Herschel spectral-line mapping of the HH211 protostellar system". Astronomy & Astrophysics 616 (agosto 2018): A84. http://dx.doi.org/10.1051/0004-6361/201833057.

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Context. Mid- and far-infrared observations of the environment around embedded protostars reveal a plethora of high-excitation molecular and atomic emission lines. A number of different mechanisms for the origin of these lines have been proposed, including shocks induced by protostellar jets and radiation by the embedded protostar interacting with its immediate surroundings. Aims. We employ extended spectral-line maps that spatially resolve regions where diverse excitation processes appear to dominate. Studying the morphology and excitation of the most important molecular and atomic coolants, we aim to constrain the physical conditions around the embedded protostellar system HH 211-mm. Methods. Spectro-imaging observations with Herschel/PACS provide emission from major molecular (CO, H2O and OH) and atomic coolants (e.g. [O I]). Emission line maps reveal the morphology of the observed emissions and allow associations between the different species. Comparisons are also made with mid-infrared line maps from Spitzer and sub-mm interferometers. The excitation conditions of the detected molecular species along with the ortho-to-para ratio of water are assessed through Boltzmann diagrams. Further investigations focus on constraining the CO/H2 ratio in shocks and the mass flux of the atomic jet as traced by [O I]. Results. Molecular lines are exited mainly at the terminal bowshocks of the outflow and around the position of the protostar. All lines show maxima at the SE bowshock with the exception of water emission that peaks around the central source. Excitation analysis in all positions shows that CO and H2O are mainly thermally excited at Tex ~ 350 and 90 K respectively, with the CO showing a second temperature component at 750 K towards the SE peak. Excitation analysis breaks down in the case of OH at the blue-shifted bowshock, indicating that the molecule is non-thermally excited. Comparisons between the CO and H2 column densities suggest that the X[CO] value in shocks can be up to an order of magnitude lower than the canonical value of 10−4. The water ortho-to-para ratio around the protostar is only 0.65, indicating low-temperature water ice formation followed by non-distructive photodesorption from the dust grains. The two-sided total atomic mass flux estimated from the [O I] jet sums to 1.65 × 10−6 M⊙ yr−1, a value that is very close to the mass flux previously estimated for the SiO jet and the H2Outflow. Conclusions. The bulk of the cooling from CO, OH and [O I] is associated with gas excited in outflow shocks, with the blue-shifted (SE) outflow showing evidence of a shock-induced UV field responsible for the OH emission. Water lines around the protostar reveal a very low ortho-to-para ratio that can be interpreted in terms of formation from a primordial gas reservoir in the envelope. Finally comparison of the [O I] jet mass flux with the mass fluxes derived for SiO and H2 renders HH 211 the first embedded system where an atomic jet is demonstrably shown to possess enough momentum to drive the observed molecular jets and large-scale outflows.

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42

DerKacy, James M., E. Baron, David Branch, Peter Hoeflich, Peter Hauschildt, Peter J. Brown e Lifan Wang. "Ultraviolet Line Identifications and Spectral Formation Near Max Light in Type Ia Supernova 2011fe". Astrophysical Journal 901, n. 1 (24 settembre 2020): 86. http://dx.doi.org/10.3847/1538-4357/abae67.

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43

Nikoghossian, A. G. "Effect of Continuum Scattering on the Statistical and Temporal Characteristics of Spectral Line Formation". Astrophysics 64, n. 3 (settembre 2021): 345–54. http://dx.doi.org/10.1007/s10511-021-09694-z.

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44

Belyaev, Andrey K. "Inelastic Collision Processes for Formation of Spectral Line Shapes in Stellar Atmospheres. Reprojection method". Journal of Physics: Conference Series 397 (6 dicembre 2012): 012052. http://dx.doi.org/10.1088/1742-6596/397/1/012052.

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45

Greve, T. R., I. Leonidaki, E. M. Xilouris, A. Weiß, Z. Y. Zhang, P. van der Werf, S. Aalto et al. "STAR FORMATION RELATIONS AND CO SPECTRAL LINE ENERGY DISTRIBUTIONS ACROSS THEJ-LADDER AND REDSHIFT". Astrophysical Journal 794, n. 2 (6 ottobre 2014): 142. http://dx.doi.org/10.1088/0004-637x/794/2/142.

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46

van den Broeke, J., P. S. Ross, A. W. C. van der Helm, E. T. Baars e L. C. Rietveld. "Use of on-line UV/Vis-spectrometry in the measurement of dissolved ozone and AOC concentrations in drinking water treatment". Water Science and Technology 57, n. 8 (1 aprile 2008): 1169–75. http://dx.doi.org/10.2166/wst.2008.137.

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Abstract (sommario):

The concentrations of dissolved ozone and assimilable organic carbon (AOC) are important performance parameters in drinking water production. For the measurement of ozone, a spectral algorithm was developed that allows quantification in situ using a UV/Vis spectrometer probe. Furthermore, a strong correlation between the change in the absorption spectrum after individual treatment steps and the formation or removal of AOC in that treatment step was observed. This allowed the development of a spectral algorithm that predicts AOC formation during ozonation and subsequent removal in further treatment steps. This method has been verified at one pilot plant of the Amsterdam drinking water supply.

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47

Couston, Laurent, Dominique Pouyat, Christophe Moulin e Pierre Decambox. "Speciation of Uranyl Species in Nitric Acid Medium by Time-Resolved Laser-Induced Fluorescence". Applied Spectroscopy 49, n. 3 (marzo 1995): 349–53. http://dx.doi.org/10.1366/0003702953963553.

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The aim of this work is the development of an on-line analytical procedure for uranyl trace determination in the nuclear fuel reprocessing process using time-resolved laser-induced fluorescence. Because the uranyl fluorescence spectrum is strongly affected by the nitrate concentration, knowledge of composition of the medium is necessary to normalize measurements. This paper reports the assumptions made on the spectral distortion, leading to a spectral deconvolution model. Uranyl complex formation constants are obtained from the spectral deconvolution and validate the method. In this way, spectral distortion allows the determination of the nitrate concentration with good accuracy.

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48

Beuther, H., Y. Wang, J. Soler, H. Linz, J. Henshaw, E. Vazquez-Semadeni, G. Gomez et al. "Dynamical cloud formation traced by atomic and molecular gas". Astronomy & Astrophysics 638 (giugno 2020): A44. http://dx.doi.org/10.1051/0004-6361/202037950.

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Context. Atomic and molecular cloud formation is a dynamical process. However, kinematic signatures of these processes are still observationally poorly constrained. Aims. We identify and characterize the cloud formation signatures in atomic and molecular gas. Methods. Targeting the cloud-scale environment of the prototypical infrared dark cloud G28.3, we employed spectral line imaging observations of the two atomic lines HI and [CI] as well as molecular lines observations in 13CO in the 1–0 and 3–2 transitions. The analysis comprises investigations of the kinematic properties of the different tracers, estimates of the mass flow rates, velocity structure functions, a histogram of oriented gradients (HOG) study, and comparisons to simulations. Results. The central infrared dark cloud (IRDC) is embedded in a more diffuse envelope of cold neutral medium traced by HI self-absorption and molecular gas. The spectral line data as well as the HOG and structure function analysis indicate a possible kinematic decoupling of the HI from the other gas compounds. Spectral analysis and position–velocity diagrams reveal two velocity components that converge at the position of the IRDC. Estimated mass flow rates appear rather constant from the cloud edge toward the center. The velocity structure function analysis is consistent with gas flows being dominated by the formation of hierarchical structures. Conclusions. The observations and analysis are consistent with a picture where the IRDC G28.3 is formed at the center of two converging gas flows. While the approximately constant mass flow rates are consistent with a self-similar, gravitationally driven collapse of the cloud, external compression (e.g., via spiral arm shocks or supernova explosions) cannot be excluded yet. Future investigations should aim at differentiating the origin of such converging gas flows.

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49

Marco, Amparo, e Ignacio Negueruela. "Triggered massive star formation in the open cluster NGC 1893". Symposium - International Astronomical Union 212 (2003): 562–63. http://dx.doi.org/10.1017/s0074180900212862.

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We have carried out a search for emission line pre-main sequence (PMS) stars in the area of the star-forming young open cluster NGC 1893 by means of slitless spectroscopy. We find 19 emission line stars with spectral types spanning the range from early B-type to G-type. All the PMS stars are confined to two small regions: the outer rim of the molecular cloud associated with the H ii region IC 410 and the vicinity of the bright emission cometary nebulae Sim 129 and Sim 130. The overall spatial distribution of PMS stars strongly suggests, that present day star formation in NGC 1893 is triggered by the O-type stars in the cluster.

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50

Giraud, E., J. Melnick, Q. S. Gu, H. Quintana, F. Selman, I. Toledo e P. Zelaya. "Galaxy Evolution in a Pilot Survey up toz=1and CDM Halos". Advances in Astronomy 2011 (2011): 1–13. http://dx.doi.org/10.1155/2011/508381.

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We study spectral evolution of galaxies in a magnitude limited sample of 550 galaxies fromz=1down toz=0.3on a pencil beam of≈10′×10′. We concentrate on the large apparent cosmological structures along the line of sight, and we bin our individual galaxy spectra to obtain representative high S/N spectra based upon these structures. We divide the resulting average spectra in three groups to facilitate the analysis:galaxies with pure absorption line spectra, galaxies with emission lines and blue continua, and galaxies with emission lines and red continua. We revisit the question of downsizing in emission-line galaxies betweenz=0.9andz=0.45in our pencil-beam and find the following results: strong star formation in emission line galaxies, aging in emission line galaxies, and aging in absorption systems, are shifting from bright to faint systems as cosmological time increases. Each redshift bin is repopulated in new starbursts. Therefore at redshiftsz⩽1galaxy formation is downsizing both in luminosity and number density. Our observations indicate that atz⩽1star formation and hierarchical structure formation of CDM halos are not in phase.

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