scholarly journals STiC: A multiatom non-LTE PRD inversion code for full-Stokes solar observations

2019 ◽  
Vol 623 ◽  
pp. A74 ◽  
Author(s):  
J. de la Cruz Rodríguez ◽  
J. Leenaarts ◽  
S. Danilovic ◽  
H. Uitenbroek
Keyword(s):  
Grid Point ◽  
Model Atmosphere ◽  
Field Vector ◽  
Oscillatory Behavior ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Solar Chromosphere ◽  
Thermodynamical Equilibrium ◽  
Partial Redistribution ◽  
Regularization Techniques

The inference of the underlying state of the plasma in the solar chromosphere remains extremely challenging because of the nonlocal character of the observed radiation and plasma conditions in this layer. Inversion methods allow us to derive a model atmosphere that can reproduce the observed spectra by undertaking several physical assumptions. The most advanced approaches involve a depth-stratified model atmosphere described by temperature, line-of-sight velocity, turbulent velocity, the three components of the magntic field vector, and gas and electron pressure. The parameters of the radiative transfer equation are computed from a solid ground of physical principles. In order to apply these techniques to spectral lines that sample the chromosphere, nonlocal thermodynamical equilibrium effects must be included in the calculations. We developed a new inversion code STiC (STockholm inversion Code) to study spectral lines that sample the upper chromosphere. The code is based on the RH forward synthesis code, which we modified to make the inversions faster and more stable. For the first time, STiC facilitates the processing of lines from multiple atoms in non-LTE, also including partial redistribution effects (PRD) in angle and frequency of scattered photons. Furthermore, we include a regularization strategy that allows for model atmospheres with a complex depth stratification, without introducing artifacts in the reconstructed physical parameters, which are usually manifested in the form of oscillatory behavior. This approach takes steps toward a node-less inversion, in which the value of the physical parameters at each grid point can be considered a free parameter. In this paper we discuss the implementation of the aforementioned techniques, the description of the model atmosphere, and the optimizations that we applied to the code. We carry out some numerical experiments to show the performance of the code and the regularization techniques that we implemented. We made STiC publicly available to the community.

scholarly journals Spectropolarimetric NLTE inversion code SNAPI

2018 ◽  
Vol 617 ◽  
pp. A24 ◽  
Author(s):  
I. Milić ◽  
M. van Noort
Keyword(s):  
Magnetic Field ◽  
Model Atmosphere ◽  
Field Vector ◽  
Spectral Lines ◽  
Local Thermal Equilibrium ◽  
Solar Chromosphere ◽  
Atmospheric Parameters ◽  
Academic Problem ◽  
Specific Implementation ◽  
The Magnetic Field

Context. Inversion codes are computer programs that fit a model atmosphere to the observed Stokes spectra, thus retrieving the relevant atmospheric parameters. The rising interest in the solar chromosphere, where spectral lines are formed by scattering, requires developing, testing, and comparing new non-local thermal equilibrium (NLTE) inversion codes. Aims. We present a new NLTE inversion code that is based on the analytical computation of the response functions. We named the code SNAPI, which is short for spectropolarimetic NLTE analytically powered inversion. Methods. SNAPI inverts full Stokes spectrum in order to obtain a depth-dependent stratification of the temperature, velocity, and the magnetic field vector. It is based on the so-called node approach, where atmospheric parameters are free to vary in several fixed points in the atmosphere, and are assumed to behave as splines in between. We describe the inversion approach in general and the specific choices we have made in the implementation. Results. We test the performance on one academic problem and on two interesting NLTE examples, the Ca II 8542 and Na I D spectral lines. The code is found to have excellent convergence properties and outperforms a finite-difference based code in this specific implementation by at least a factor of three. We invert synthetic observations of Na lines from a small part of a simulated solar atmosphere and conclude that the Na lines reliably retrieve the magnetic field and velocity in the range −3 <  logτ <  −0.5.

scholarly journals Comparison of theoretical and observed Ca II 8542 Stokes profiles in quiet regions at the centre of the solar disc

2018 ◽  
Vol 619 ◽  
pp. A60 ◽  
Author(s):  
J. Jurčák ◽  
J. Štěpán ◽  
J. Trujillo Bueno ◽  
M. Bianda
Keyword(s):  
Radiative Transfer ◽  
3D Model ◽  
Model Atmosphere ◽  
Spectral Lines ◽  
Stokes Parameters ◽  
Solar Disc ◽  
Solar Chromosphere ◽  
Line Profiles ◽  
Forward Modelling ◽  
Radiation Magnetohydrodynamics

Context. Interpreting the Stokes profiles observed in quiet regions of the solar chromosphere is a challenging task. The Stokes Q and U profiles are dominated by the scattering polarisation and the Hanle effect, and these processes can only be correctly quantified if 3D radiative transfer effects are taken into account. Forward-modelling of the intensity and polarisation of spectral lines using a 3D model atmosphere is a suitable approach in order to statistically compare the theoretical and observed line profiles. Aims. Our aim is to present novel observations of the Ca II 8542 Å line profiles in a quiet region at the centre of the solar disc and to quantitatively compare them with the theoretical Stokes profiles obtained by solving the problem of the generation and transfer of polarised radiation in a 3D model atmosphere. We aim at estimating the reliability of the 3D model atmosphere, excluding its known lack of dynamics and/or insufficient density, using not only the line intensity but the full vector of Stokes parameters. Methods. We used data obtained with the ZIMPOL instrument at the Istituto Ricerche Solari Locarno (IRSOL) and compared the observations with the theoretical profiles computed with the PORTA radiative transfer code, using as solar model atmosphere a 3D snapshot taken from a radiation-magnetohydrodynamics simulation. The synthetic profiles were degraded to match the instrument and observing conditions. Results. The degraded theoretical profiles of the Ca II 8542 line are qualitatively similar to the observed ones. We confirm that there is a fundamental difference in the widths of all Stokes profiles: the observed lines are wider than the theoretical lines. We find that the amplitudes of the observed profiles are larger than those of the theoretical ones, which suggests that the symmetry breaking effects in the solar chromosphere are stronger than in the model atmosphere. This means that the isosurfaces of temperature, velocity, and magnetic field strength and orientation are more corrugated in the solar chromosphere than in the currently available 3D radiation-magnetohydrodynamics simulation.

Non-L.T.E. Analysis of Spectral Lines

1970 ◽  
Vol 1 (7) ◽  
pp. 296-301
Author(s):  
D. Mugglestone
Keyword(s):  
Optical Depth ◽  
Solar Atmosphere ◽  
Model Atmosphere ◽  
Gas Pressure ◽  
Stellar Atmospheres ◽  
Basic Theory ◽  
Spectral Lines ◽  
Absorption Lines ◽  
Physical Parameters ◽  
Electron Pressure

At a previous meeting of the Society I well remember Paul Wild saying, in a humorous vein of course, that until recently he had always thought that an H-R diagram was a plot of H against R. It occurs to me that the same kind of vagueness, although perhaps not to the same degree, might be present with astronomers not directly concerned with the theory of stellar atmospheres in regard to ‘L.T.E.’ and ‘Non-L.T.E.’ analysis of spectral lines. In the present paper, I would like to point out some of the important features of non-L.T.E. analysis, to indicate how the basic theory may be developed, and to show what effect this has on the theoretically produced absorption lines. I will make particular reference to the solar atmosphere and here we take the ‘model atmosphere’ approach where all the physical parameters such as gas pressure, electron pressure, temperature etc., are all specified as functions of optical depth.

scholarly journals Solar spectral irradiance variability of some chromospheric emission lines through the solar activity cycles 21-23

2017 ◽  
pp. 71-86
Author(s):  
Ü.D. Göker ◽  
M.Sh. Gigolashvili ◽  
N. Kapanadze
Keyword(s):  
Solar Activity ◽  
Chemical Elements ◽  
Wave Length ◽  
Spectral Lines ◽  
Spectral Irradiance ◽  
Close Connection ◽  
Solar Chromosphere ◽  
Solar Spectral Irradiance ◽  
Activity Cycles ◽  
Solar Activity Cycles

A study of variations of solar spectral irradiance (SSI) in the wave-length ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. We used various data for ultraviolet (UV) spectral lines and international sunspot number (ISSN) from interactive data centers such as SME (NSSDC), UARS (GDAAC), SORCE (LISIRD) and SIDC, respectively. We reduced these data by using the MATLsoftware package. In this respect, we revealed negative correlations of intensities of UV (289.5 nm-300.5 nm) spectral lines originating in the solar chromosphere with the ISSN index during the unusually prolonged minimum between the solar activity cycles (SACs) 23 and 24. We also compared our results with the variations of solar activity indices obtained by the ground-based telescopes. Therefore, we found that plage regions decrease while facular areas are increasing in SAC 23. However, the decrease in plage regions is seen in small sunspot groups (SGs), contrary to this, these regions in large SGs are comparable to previous SACs or even larger as is also seen in facular areas. Nevertheless, negative correlations between ISSN and SSI data indicate that these variations are in close connection with the classes of sunspots/SGs, faculae and plage regions. Finally, we applied the time series analysis of spectral lines corresponding to the wavelengths 121.5 nm-300.5 nm and made comparisons with the ISSN data. We found an unexpected increase in the 298.5 nm line for the Fe II ion. The variability of Fe II ion 298.5 nm line is in close connection with the facular areas and plage regions, and the sizes of these solar surface indices play an important role for the SSI variability, as well. So, we compared the connection between the sizes of faculae and plage regions, sunspots/SGs, chemical elements and SSI variability. Our future work will be the theoretical study of this connection and developing of a corresponding model.

scholarly journals INTERSTELLAR MEDIUM AND DECAMETER RADIO SPECTROSCOPY

2021 ◽  
Vol 26 (4) ◽  
pp. 314-325
Author(s):  
S. V. Stepkin ◽  
◽  
O. O. Konovalenko ◽  
Y. V. Vasylkivskyi ◽  
D. V. Mukha ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Low Frequency ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Recombination Mechanism ◽  
Radio Recombination Lines ◽  
Radio Spectroscopy ◽  
Correlation Spectrum

Purpose: The analytical review of the main results of research in the new direction of the low-frequency radio astronomy, the interstellar medium radio spectroscopy at decameter waves, which had led to astrophysical discovery, recording of the radio recombination lines in absorption for highly excited states of interstellar carbon atoms (more than 600). Design/methodology/approach: The UTR-2 world-largest broadband radio telescope of decameter waves optimally connected with the digital correlation spectrum analyzers has been used. Continuous modernization of antenna system and devices allowed increasing the analysis band from 100 kHzto 24 MHz and a number of channels from 32 to 8192. The radio telescope and receiving equipment with appropriate software allowed to have a long efficient integration time enough for a large line series simultaneously with high resolution, noise immunity and relative sensitivity. Findings: A new type of interstellar spectral lines has been discovered and studied, the interstellar carbon radio recombination lines in absorption for the record high excited atoms with principal quantum numbers greater than 1000. The line parameters (intensity, shape, width, radial velocity) and their relation ship with the interstellar medium physical parameters have been determined. The temperature of line forming regions is about 100 K, the electron concentration up to 0.1 cm–3 and the size of a line forming region is about 10 pc. For the first time, radio recombination lines were observed in absorption. They have significant broadening and are amplified by the dielectronic-like recombination mechanism and are also the lowest frequency lines in atomic spectroscopy. Conclusions: The detected low-frequency carbon radio recombination lines and their observations have become a new highly effective tool for the cold partially ionized interstellar plasma diagnostics. Using them allows obtaining the information which is not available with the other astrophysical methods. For almost half a century of their research, a large amount of hardware-methodical and astrophysical results have been obtained including a record number of Galaxy objects, where there levant lines have been recorded. The domestic achievements have stimulated many theoretical and experimental studies in other countries, but the scientific achievements of Ukrainian scientists prove the best prospects for further development of this very important area of astronomical science. Key words: low-frequency radio astronomy; radio telescope; interstellar medium; radio recombination lines; carbon; hydrogen; spectral analyzer

scholarly journals Diagnostics for spectropolarimetry and magnetography

2010 ◽  
Vol 6 (S273) ◽  
pp. 37-43
Author(s):  
Jose Carlos del Toro Iniesta ◽  
Valentín Martínez Pillet
Keyword(s):  
Analytical Approach ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Instrumental Effects ◽  
Response Functions

AbstractAn assessment on the capabilities of modern spectropolarimeters and magnetographs is in order since most of our astrophysical results rely upon the accuracy of the instrumentation and on the sensitivity of the observables to variations of the sought physical parameters. A contribution to such an assessment will be presented in this talk where emphasis will be made on the use of the so-called response functions to gauge the probing capabilities of spectral lines and on an analytical approach to estimate the uncertainties in the results in terms of instrumental effects. The Imaging Magnetograph eXperiment (IMaX) and the Polarimetric and Helioseismic Imager (PHI) will be used as study cases.

scholarly journals UV core dimming in coronal streamer belt and the projection effects

2019 ◽  
Vol 623 ◽  
pp. A95 ◽  
Author(s):  
L. Abbo ◽  
S. Giordano ◽  
L. Ofman
Keyword(s):  
Magnetic Structure ◽  
Heavy Ions ◽  
Solar Minimum ◽  
Heavy Ion ◽  
Spectral Lines ◽  
Slow Solar Wind ◽  
Physical Parameters ◽  
Streamer Belt ◽  
Coronal Streamer ◽  
Tilted Dipole

During solar minimum activity, the coronal structure is dominated by a tilted streamer belt, associated with the sources of the slow solar wind. It is known that some UV coronal spectral observations show a quite evident core dimming in heavy ions emission in quiescent streamers. In this paper, our purpose is to investigate this phenomenon by comparing observed and simulated UV coronal ion spectral line intensities. First, we computed the emissivities and the intensities of HI Lyα and OVI spectral lines starting from the physical parameters of a time-dependent 3D three-fluid MHD model of the coronal streamer belt. The model is applied to a tilted dipole (10°) solar minimum magnetic structure. Next, we compared the results obtained from the model in the extended corona (from 1.5 to 4 R⊙) to the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO during the minimum of solar activity (1996). We investigate the line-of-sight integration and projection effects in the UV spectroscopic observations, disentangled by the 3D multifluid model. The results demonstrate that the core dimming in heavy ions is produced by the physical processes included in the model (i.e., combination of the effects of heavy ion gravitational settling, and energy exchange of the preferentially heated heavy ions through the interaction with electrons and protons) but it is visible only in some cases where the magnetic structure is simple, such as a (tilted) dipole.

Lyman-alpha rocket spectra and models of the quiet and active solar chromosphere based on partial redistribution diagnostics

1979 ◽  
Vol 230 ◽  
pp. 924 ◽  
Author(s):  
G. S. Basri ◽  
J. L. Linsky ◽  
J.-D. F. Bartoe ◽  
G. Brueckner ◽  
M. E. van Hoosier
Keyword(s):  
Solar Chromosphere ◽  
Lyman Alpha ◽  
Partial Redistribution

Non-local thermodynamical equilibrium abundance analysis of singly ionized praseodymium for the Sun

2020 ◽  
Vol 496 (4) ◽  
pp. 5361-5371
Author(s):  
Abdelrazek M K Shaltout ◽  
Ali G A Abdelkawy ◽  
M M Beheary
Keyword(s):  
Spectral Lines ◽  
Oscillator Strengths ◽  
Atomic Data ◽  
Dimensional Model ◽  
Thermodynamical Equilibrium ◽  
Solar Abundance ◽  
One Dimensional ◽  
Microturbulent Velocity ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

ABSTRACT Determinations of the solar abundance of praseodymium (Pr) depend critically on the local thermodynamical equilibrium (LTE) and non-local thermodynamical equilibrium (NLTE) techniques beyond the capabilities of a classical one-dimensional model atmosphere. Here, in this analysis, we adopt an atomic model atom of Pr consisting of 105 energy levels and 14 bound–bound transitions of singly ionized praseodymium (Pr ii) and the ground state of the Pr iii continuum limit. We briefly analyse the solar abundance of Pr taking the solar model atmospheres of Holweger & Müller (1974, Solar Physics, 39, 19) with the measured equivalent linewidths and invoking a microturbulent velocity treatment. We succeed in accurately selecting nearby clear sections of the spectrum for 14 spectral lines of Pr ii with the improved atomic data of high-quality oscillator strengths available from the laboratory measurements of several possible sources as well as accurate damping constants successfully determined from the literature. We find a Pr abundance revised to be downwards log ϵPr(NLTE) = 0.75 ± 0.09, which is in good agreement with the meteoritic value (log ϵPr = 0.76 ± 0.03). A comparison of the NLTE abundance corrections with the standard LTE analysis, log ϵPr(LTE) = 0.74 ± 0.08, reveals a positive correction of  +0.01 dex, estimated from the selected solar Pr ii lines. The Pr abundance value is clearly superior following the classical one-dimensional model atmospheres of Holweger & Müller, the absolute scales of gf-values, the microturbulent velocity and the adopted equivalent linewidths.

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