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Context. Rigorous modeling of the ion{Ba}{ii} ${lambda}4554$ formation is potentially interesting since this strongly polarized line forms in the solar chromosphere where the magnetic field is rather poorly known. Aims. To investigate the role of isotropic collisions with neutral hydrogen in the formation of the polarized ion{Ba}{ii} ${lambda}4554$ line and, thus, in the determination of the magnetic field. Methods. Multipole relaxation and transfer rates of the $d$ and p-states of ion{Ba}{ii} by isotropic collisions with neutral hydrogen are calculated. We consider a plane parallel layer of ion{Ba}{ii} situated at the low chromosphere and anisotropically illuminated from below which produces linear polarization in the ${lambda}4554$ line by scattering processes. To compute that polarization, we solve the statistical equilibrium equations for ion{Ba}{ii} levels including collisions, radiation and magnetic field effects. Results. Variation laws of the relaxation and transfer rates with hydrogen number density $n_{textrm {scriptsize H}}$ and temperature are deduced. The polarization of the ${lambda}4554$ line is clearly affected due to isotropic collisions with neutral hydrogen although the collisional depolarization of its upper level $^2P_{3/2}$ is negligible. This is because the alignment of the metastable levels $^2D_{3/2}$ and $^2D_{5/2}$ of the ion{Ba}{ii} are vulnerable to collisions. At the height of formation of the ${lambda}4554$ line where $n_{textrm {scriptsize H}} sim 2 times 10^{14}$ cm$^{-3}$, we find that the neglecting of the collisions induces inaccuracy of $sim$ 25% on the calculation of the polarization and $sim$ 35 % inaccuracy on microturbulent magnetic field determination.
This work aims to provide key elements to gain better understanding of the formation of the second solar spectrum of the Sr II $lambda$4078 line. We show that in a certain range of hydrogen density, the effect of isotropic collisions between Sr II io
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The structure and energy balance of the solar chromosphere remain poorly known. We have used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Halpha and Ca II 854.2 nm over a sizab
We present joint observations of the Sun by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). The observations were made of a solar active region on 2015 December 18 as part of the ALMA scie
Low-temperature specific heat (SH) is measured on Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ single crystals in a wide doping region under different magnetic fields. For the overdoped sample, we find the clear evidence for the presence of $T^2$ term in the dat