scholarly journals Physical properties of bright Ca II K fibrils in the solar chromosphere

2020 ◽  
Vol 637 ◽  
pp. A1 ◽  
Author(s):  
Sepideh Kianfar ◽  
Jorrit Leenaarts ◽  
Sanja Danilovic ◽  
Jaime de la Cruz Rodríguez ◽  
Carlos José Díaz Baso
Keyword(s):  
Physical Properties ◽  
Local Thermodynamic Equilibrium ◽  
Broad Band ◽  
Active Regions ◽  
Line Of Sight ◽  
Solar Chromosphere ◽  
Line Profiles ◽  
Surrounding Atmosphere ◽  
Plage Region ◽  
Non Local

Context. Broad-band images of the solar chromosphere in the Ca II H&K line cores around active regions are covered with fine bright elongated structures called bright fibrils. The mechanisms that form these structures and cause them to appear bright are still unknown. Aims. We aim to investigate the physical properties, such as temperature, line-of-sight velocity, and microturbulence, in the atmosphere that produces bright fibrils and to compare those to the properties of their surrounding atmosphere. Methods. We used simultaneous observations of a plage region in Fe I 6301-2 Å, Ca II 8542 Å, Ca II K, and Hα acquired by the CRISP and CHROMIS instruments on the Swedish 1 m Solar Telescope. We manually selected a sample of 282 Ca II K bright fibrils. We compared the appearance of the fibrils in our sample to the Ca II 8542 Å and Hα data. We performed non-local thermodynamic equilibrium inversions using the inversion code STiC on the Fe I 6301-2 Å, Ca II 8542 Å, and Ca II K lines to infer the physical properties of the atmosphere. Results. The line profiles in bright fibrils have a higher intensity in their K2 peaks compared to profiles formed in the surrounding atmosphere. The inversion results show that the atmosphere in fibrils is on average  −100 K hotter at an optical depth log(τ500 nm) = −4.3 compared to their surroundings. The line-of-sight velocity at chromospheric heights in the fibrils does not show any preference towards upflows or downflows. The microturbulence in the fibrils is on average 0.5 km s−1 higher compared to their surroundings. Our results suggest that the fibrils have a limited extent in height, and they should be viewed as hot threads pervading the chromosphere.

scholarly journals The influence of NLTE effects in Fe I lines on an inverted atmosphere

2020 ◽  
Vol 633 ◽  
pp. A157 ◽  
Author(s):  
H. N. Smitha ◽  
R. Holzreuter ◽  
M. van Noort ◽  
S. K. Solanki
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Solar Physics ◽  
Accurate Determination ◽  
Line Of Sight ◽  
Line Pair ◽  
Line Profiles ◽  
Magnetic Elements ◽  
Non Local ◽  
Magnetohydrodynamic Simulation

Context. Ultraviolet overionisation of iron atoms in the solar atmosphere leads to deviations in their level populations based on Saha-Boltzmann statistics. This causes their line profiles to form in non-local thermodynamic equilibrium (NLTE) conditions. When inverting such profiles to determine atmospheric parameters, the NLTE effects are often neglected and other quantities are tweaked to compensate for deviations from the LTE. Aims. We investigate how the routinely employed LTE inversion of iron lines formed in NLTE underestimates or overestimates atmospheric quantities, such as temperature (T), line-of-sight velocity (vLOS), magnetic field strength (B), and inclination (γ) while the earlier papers have focused mainly on T. Our findings has wide-ranging consequences since many results derived in solar physics are based on inversions of Fe I lines carried out in LTE. Methods. We synthesized the Stokes profiles of Fe I 6301.5 Å and 6302.5 Å lines in both LTE and NLTE using a snapshot of a 3D magnetohydrodynamic simulation. The profiles were then inverted in LTE. We considered the atmosphere inferred from the inversion of LTE profiles as the fiducial model and compared it to the atmosphere resulting from the inversion of NLTE profiles. The observed differences have been attributed to NLTE effects. Results. Neglecting the NLTE effects introduces errors in the inverted atmosphere. While the errors in T can go up to 13%, in vLOS and B, the errors can go as high as 50% or above. We find these errors to be present at all three inversion nodes. Importantly, they survive degradation from the spatial averaging of the profiles. Conclusions. We provide an overview of how neglecting NLTE effects influences the values of T, vLOS, B, and γ that are determined by inverting the Fe I 6300 Å line pair, as observed, for example, by Hinode/SOT/SP. Errors are found at the sites of granules, intergranular lanes, magnetic elements, and basically in every region susceptible to NLTE effects. For an accurate determination of the atmospheric quantities and their stratification, it is, therefore, important to take the NLTE effects into account.

scholarly journals 2D non-LTE modelling of a filament observed in the Hα line with the DST/IBIS spectropolarimeter

2019 ◽  
Vol 631 ◽  
pp. A146 ◽  
Author(s):  
P. Schwartz ◽  
S. Gunár ◽  
J. M. Jenkins ◽  
D. M. Long ◽  
P. Heinzel ◽  
...  
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Line Of Sight ◽  
Solar Telescope ◽  
Line Profiles ◽  
Forward Modelling ◽  
Dynamic Nature ◽  
Synthetic Spectra ◽  
Quiescent Stage ◽  
2D Model ◽  
Quiescent Filament

Context. We study a fragment of a large quiescent filament observed on May 29, 2017 by the Interferometric BIdimensional Spectropolarimeter (IBIS) mounted at the Dunn Solar Telescope. We focus on its quiescent stage prior to its eruption. Aims. We analyse the spectral observations obtained in the Hα line to derive the thermodynamic properties of the plasma of the observed fragment of the filament. Methods. We used a 2D filament model employing radiative transfer computations under conditions that depart from the local thermodynamic equilibrium. We employed a forward modelling technique in which we used the 2D model to produce synthetic Hα line profiles that we compared with the observations. We then found the set of model input parameters, which produces synthetic spectra with the best agreement with observations. Results. Our analysis shows that one part of the observed fragment of the filament is cooler, denser, and more dynamic than its other part that is hotter, less dense, and more quiescent. The derived temperatures in the first part range from 6000 K to 10 000 K and in the latter part from 11 000 K to 14 000 K. The gas pressure is 0.2–0.4 dyn cm−2 in the first part and around 0.15 dyn cm−2 in the latter part. The more dynamic nature of the first part is characterised by the line-of-sight velocities with absolute values of 6–7 km s−1 and microturbulent velocities of 8–9 km s−1. On the other hand, the latter part exhibits line-of-sight velocities with absolute values 0–2.5 km s−1 and microturbulent velocities of 4–6 km s−1.

scholarly journals Chromospheric heating during flux emergence in the solar atmosphere

2018 ◽  
Vol 612 ◽  
pp. A28 ◽  
Author(s):  
Jorrit Leenaarts ◽  
Jaime de la Cruz Rodríguez ◽  
Sanja Danilovic ◽  
Göran Scharmer ◽  
Mats Carlsson
Keyword(s):  
Linear Polarization ◽  
Active Regions ◽  
Spatial And Temporal Variation ◽  
Solar Chromosphere ◽  
Gas Temperature ◽  
Horizontal Magnetic Field ◽  
Magnetic Elements ◽  
Spatially Extended ◽  
Non Local ◽  
Radiative Losses

Context. The radiative losses in the solar chromosphere vary from 4 kW m−2 in the quiet Sun, to 20 kW m−2 in active regions. The mechanisms that transport non-thermal energy to and deposit it in the chromosphere are still not understood. Aim. We aim to investigate the atmospheric structure and heating of the solar chromosphere in an emerging flux region. Methods. We have used observations taken with the CHROMIS and CRISP instruments on the Swedish 1-m Solar Telescope in the Ca II K , Ca II 854.2 nm, Hα, and Fe I 630.1 nm and 630.2 nm lines. We analysed the various line profiles and in addition perform multi-line, multi-species, non-local thermodynamic equilibrium (non-LTE) inversions to estimate the spatial and temporal variation of the chromospheric structure. Results. We investigate which spectral features of Ca II K contribute to the frequency-integrated Ca II K brightness, which we use as a tracer of chromospheric radiative losses. The majority of the radiative losses are not associated with localised high-Ca II K-brightness events, but instead with a more gentle, spatially extended, and persistent heating. The frequency-integrated Ca II K brightness correlates strongly with the total linear polarization in the Ca II 854.2 nm, while the Ca II K profile shapes indicate that the bulk of the radiative losses occur in the lower chromosphere. Non-LTE inversions indicate a transition from heating concentrated around photospheric magnetic elements below log τ500 = −3 to a more space-filling and time-persistent heating above log τ500 = −4. The inferred gas temperature at log τ500 = −3.8 correlates strongly with the total linear polarization in the Ca II 854.2 nm line, suggesting that that the heating rate correlates with the strength of the horizontal magnetic field in the low chromosphere.

Structuring, Motions and Shapes of Corona Emission Line Profiles

1994 ◽  
Vol 144 ◽  
pp. 421-426
Author(s):  
N. F. Tyagun
Keyword(s):  
Emission Line ◽  
Filling Factor ◽  
Direct Relationship ◽  
Coronal Plasma ◽  
Line Of Sight ◽  
Line Profiles ◽  
The Difference ◽  
Yellow Line ◽  
Red Line

AbstractThe interrelationship of half-widths and intensities for the red, green and yellow lines is considered. This is a direct relationship for the green and yellow line and an inverse one for the red line. The difference in the relationships of half-widths and intensities for different lines appears to be due to substantially dissimilar structuring and to a set of line-of-sight motions in ”hot“ and ”cold“ corona regions.When diagnosing the coronal plasma, one cannot neglect the filling factor - each line has such a factor of its own.

Diagnosing Fe Plasma In Non-Local Thermodynamic Equilibrium

2013 ◽  
Vol 82 (2) ◽  
pp. 024501
Author(s):  
Xiao-Ying Han ◽  
Fei-Lu Wang ◽  
Ze-Qing Wu ◽  
Jun Yan ◽  
Gang Zhao
Keyword(s):  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Non Local

scholarly journals The Influence of Chemi-Ionization and Recombination Processes on Spectral Line Shapes in Stellar Atmospheres

2011 ◽  
Vol 20 (4) ◽  
Author(s):  
Anatolij A. Mihajlov ◽  
Ljubinko M. Ignjatović ◽  
Vladimir A. Srécković ◽  
Milan S. Dimitrijević
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Rydberg Atom ◽  
Stellar Atmospheres ◽  
Line Shapes ◽  
Red Dwarfs ◽  
Recombination Processes ◽  
Weakly Ionized ◽  
Non Local ◽  
Factors Of Influence ◽  
Ionization Processes

AbstractThe chemi-ionization processes in atom - Rydberg atom collisions, as well as the corresponding chemi-recombination processes, are considered as factors of influence on the atom exited-state populations in weakly ionized layers of stellar atmospheres. The presented results are related to the photospheres of the Sun and some M red dwarfs, as well as weakly ionized layers of DB white dwarf atmospheres. It has been found that the mentioned chemi-ionization and recombination processes dominate over the concurrent electron-atom and electron-ion ionization and recombination processes in all parts of the considered stellar atmospheres. The obtained results demonstrate the fact that the considered processes must have significant influence on the optical properties of stellar atmospheres. It is shown that these processes and their importance for non-local thermodynamic equilibrium (non-LTE) modeling of the solar atmospheres should be investigated further.

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