arXiv subjects

Tanausú del Pino Alemán

Publications and source records attributed to Tanausú del Pino Alemán.

At least 19 recordsLinked to original sources

arXiv2026

Observational insights into Sr I 4607 Å scattering polarization with DKIST/ViSP

Scattering polarization signals in the Sr I 4607 Å spectral line are among the strongest originating from the solar photosphere, offering a powerful diagnostic of tangled magnetic fields in the 3--300 G range via the Hanle effect. However, measuring them with sub-arcsec resolution remains a significant challenge. We analyze spatially resolved quiet-Sun observations of these signals performed with the Visible Spectropolarimeter (ViSP) at the Daniel K. Inouye Solar Telescope (DKIST) and identify its current observational limits. We present high-resolution, high-precision spectropolarimetric observations in a spectral window including the Sr I 4607 Å line at various limb distances. We apply consistent instrumental corrections across all spectral lines, enabling the adjacent lines to serve as reliable references. At a limb distance of $μ= 0.74$, the signal-to-noise ratio is low but sufficient in the total linear polarization map to directly reveal sub-arcsec structures in the Sr I line for the first time, which can be attributed to scattering polarization. Disk-center measurements are still dominated by noise related to the current limitations of the observational setup. By combining high spatio-temporal and spectral resolution with exceptional polarimetric precision, DKIST enables measurements of solar photospheric scattering polarization at fine scales. However, current signal-to-noise limitations still hinder direct detection of disk-center scattering polarization and must be addressed before further progress can be made.

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arXiv2026

3D radiative transfer modeling of scattering polarization with partial frequency redistribution I. Verification and disk-center results for the solar Ca I 4227 Å line

Several strong solar resonance lines show observable linear scattering polarization signals, holding a great potential for investigating the magnetism of the outer solar atmosphere. Accurately modeling these signals requires solving the radiative transfer (RT) problem for polarized radiation in comprehensive 3D models of the solar atmosphere, in non-local thermodynamic equilibrium, accounting for partial frequency redistribution (PRD) effects. This problem has so far been computationally inaccessible. We present the first scientific application of TRIP, a novel software for the massively parallel solution of the 3D non-LTE RT problem for polarized radiation, including scattering polarization and PRD. We aim to verify the code and explore the combined action of PRD and the 3D structure of the solar atmosphere on scattering polarization. We run TRIP to synthesize the Stokes profiles of the Ca I line at 4227 Å in a 3D model of the solar atmosphere extracted from a radiation magneto-hydrodynamic simulation. We efficiently solve the resulting large-scale problem, with up to $4 \times 10^{10}$ degrees of freedom, with a state-of-the-art preconditioned Krylov method, using up to 20 thousand parallel CPUs. After including verification tests, we find that the joint impact of PRD effects and the detailed 3D structure of the atmospheric model produce disk-center scattering polarization signals in the line wings. These signals are sensitive to the magnetic field, via magneto-optical effects, and to bulk velocity gradients. We also show that the CRD approximation underestimates the amplitude of disk-center line-core signals. This achievement represents a crucial step forward for diagnosing the magnetism of the solar chromosphere and transition region through the quantitative comparisons of synthetic and observational data.

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arXiv2025

Inferring Solar Magnetic fields From the Polarization of the Mg II h and k Lines

The polarization of the Mg II h and k lines holds significant diagnostic potential for measuring chromospheric magnetic fields, which are crucial for understanding the physical processes governing the energy transport and dissipation in the solar upper atmosphere, as well as the subsequent heating of the chromosphere and corona. The Chromospheric Layer Spectropolarimeter was launched twice in 2019 and 2021, successfully acquiring spectropolarimetric observations across the Mg II h and k lines. The analysis of these observations confirms the capability of these lines for inferring magnetic fields in the upper chromosphere. In this review, we briefly introduce the physical mechanisms behind the polarization of the Mg II h and k lines, including the joint action of the Zeeman and Hanle effects, the magneto-optical effect, partial frequency redistribution, and atomic level polarization. We also provide an overview of recent progress in the interpretation of the Stokes profiles of the Mg II h and k lines.

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arXiv2025

DKIST resolves sub-arcsec photospheric scattering polarization

Scattering polarization signals offer a unique diagnostics of the physical conditions in the solar atmosphere, in particular magnetic fields via the Hanle effect. However, their spatial structure remains poorly constrained due to the difficulty of achieving high spatial resolution and polarimetric sensitivity simultaneously. We present the first direct observation of sub-arcsecond structuring in the linear scattering polarization of the photospheric Sr i 4607 Å\, line near the solar disk center ($μ$ = 0.74), obtained with the Visible Spectro- Polarimeter (ViSP) at the Daniel K. Inouye Solar Telescope (DKIST). The data achieve about 0".2 resolution with 30 s integration and sufficient sensitivity to detect fine-scale patterns in the total linear polarization, which are evident in Sr i but absent in a nearby Fe i line that is simultaneously observed. Since this Fe i line is more Zeeman-sensitive than the Sr i 4607 Å\, this disparity confirms that the signals in the Sr i 4607 Å\, line arise from scattering. These data provide the first spatially resolved two-dimensional maps of photospheric scattering polarization at sub-arcsecond scales, enabled by the capabilities of a 4-meter solar telescope.

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arXiv2025

Determining the magnetic field of active region plages using the whole CLASP2/2.1 spectral window

The Chromospheric LAyer SpectroPolarimeter missions, CLASP2 and CLASP2.1, demonstrated that the near-UV spectral region between 279.30 and 280.68 nm is suitable for studying the magnetism of the solar chromosphere. In particular, the spectropolarimetric observations in the Mg II h and k resonant doublet, Mn I 279.91 and 280.19 nm resonant lines, and Fe II 279.79 and 280.66 nm lines acquired by these suborbital space experiments have been proven useful for inferring the magnetic field stratification in the solar chromosphere. However, several lines of the CLASP2/2.1 spectral region with significant circular polarization signals had remained unexplored. After identifying two Ni I (279.95 and 280.59 nm), one Mn II (280.62 nm), and one Fe I (280.53 nm) lines, here we apply the Weak Field Approximation (WFA) to the spectropolarimetric observations of active region plages by CLASP2 and CLASP2.1. By comparing the results with previous studies, we are able to estimate the formation heights of these CLASP2/2.1 additional spectral lines and to demonstrate their suitability to determine the magnetic field stratification from the photosphere to the upper chromosphere.

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arXiv2025

Determining the Magnetic Field in the Atmosphere of a Solar Active Region Observed by the CLASP2.1 Sounding Rocket Experiment

We determine magnetic fields from the photosphere to the upper chromosphere combining data from the Hinode satellite and the CLASP2.1 sounding rocket experiment. CLASP2.1 provided polarization profiles of the Mg~{|sc ii} $h$ and $k$ lines, as well as of the Mn~{|sc i} lines around 2800~{|AA}, across various magnetic structures in an active region, containing a plage, a pore, and the edges of a sunspot penumbra. By applying the Weak-Field Approximation (WFA) to the circular polarization profiles of these spectral lines, we obtain a longitudinal magnetic field map at three different heights in the chromosphere (lower, middle, and upper). This is complemented by data from Hinode (photospheric magnetic field), IRIS, and SDO (high-spatial-resolution observations of the chromosphere and corona). We quantify the height expansion of the plage magnetic fields and find that the magnetic fields expand significantly in the middle chromosphere, shaping the moss observed above in the transition region and corona. We identified an area with polarity reversal at the upper chromosphere around the edge of the pore, suggesting the presence of a magnetic discontinuity in the upper chromosphere. Transient and recurrent jet-like events are observed in this region, likely driven by magnetic reconnection. Around the penumbral edge, we find large-scale magnetic fields corresponding to the superpenumbral fibrils seen in the upper chromosphere. In the superpenumbral fibrils, we find Zeeman-induced linear polarization signals, suggesting the presence of a significantly inclined magnetic field, as strong as 1000~G in the upper chromosphere.

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arXiv2025

A numerical approach for modelling the polarisation signals of strong resonance lines with partial frequency redistribution. Numerical applications to two-term atoms and plane-parallel atmospheres

Aims. The main goal of this paper is to present an accurate and efficient numerical strategy for solving the radiative transfer problem for polarised radiation in strong resonance lines forming out of local thermodynamic equilibrium, taking angle-dependent (AD) partial frequency redistribution (PRD) effects and J-state interference into account. We consider the polarisation produced both by the Zeeman effect and by the scattering of anisotropic radiation, along with its sensitivity to the Hanle and magneto-optical effects. Methods. We introduce a formalism that allows treating both a two-level and a two-term atom in the presence of arbitrary magnetic and bulk velocity fields. The problem is formulated by treating the population of the lower level/term as a fixed input parameter. This approach makes the problem linear with respect to the radiation field, enabling the application of efficient matrix-free preconditioned iterative methods for its solution. Additionally, the computation of the scattering emissivity in the comoving frame, together with a careful choice of the angular and spectral quadrature nodes, allow us to speed up the calculations by reducing the number of evaluations of the redistribution functions. Results. The proposed solution strategy is applied to synthesise the Stokes profiles of the Mg ii h&k doublet and the H i Ly-α line in 1D semi-empirical models. The results demonstrate that the method is both fast and accurate. A comparison with calculations from HanleRT-TIC displays an overall good agreement, thereby validating our solution strategy. Moreover, for the wavelength-integrated polarisation profiles of the H i Ly-α line, we find an excellent agreement between the results obtained including PRD effects in their general AD description and those obtained considering the angle-averaged simplifying approximation.

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arXiv2025

P-CORONA: A New Tool for Calculating the Intensity and Polarization of Coronal Lines in 3D Models of the Solar Corona

The critical need to study the magnetic field in the solar corona is highlighted by recent observational facilities, such as DKIST and Aditya-L1. A powerful tool for probing the magnetism of the solar corona is forward modeling of the intensity and polarization of coronal emission lines in three-dimensional (3D) magnetohydrodynamic models. Here we present P-CORONA, a new spectral synthesis code designed to calculate the intensity and polarization of coronal lines in 3D models of the solar corona, taking into account the symmetry breaking induced by magnetic and velocity fields. P-CORONA allows the calculation of the on-disk and off-limb intensity and polarization of forbidden and permitted coronal lines, thus facilitating a wide range of investigations. Applying the quantum theory of atom-photon interactions, P-CORONA accounts for the spectral line polarization caused by anisotropic radiation pumping and the Hanle and Zeeman effects, making it a valuable tool for investigating coronal magnetic fields. This paper details the code's theoretical formulation, the implementation, and illustrative results of calculations in different 3D coronal models (MURaM and Predictive Science Inc.), including the impact of the Zeeman effect from the transverse magnetic field component on selected coronal forbidden lines. P-CORONA is now accessible to the research community on GitLab and Zenodo, providing a resource to facilitate research aimed at advancing our understanding of coronal magnetism and dynamics.

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arXiv2024

Full Stokes-vector inversion of the solar Mg II h & k lines

The polarization of the Mg II h & k resonance lines is the result of the joint action of scattering processes and the magnetic field induced Hanle, Zeeman, and magneto-optical effects, thus holding significant potential for the diagnostic of the magnetic field in the solar chromosphere. The Chromospheric LAyer Spectro-Polarimeter sounding rocket experiment, carried out in 2019, successfully measured at each position along the 196 arcsec spectrograph slit the wavelength variation of the four Stokes parameters in the spectral region of this doublet around 280 nm, both in an active region plage and in a quiet region close to the limb. We consider some of these CLASP2 Stokes profiles and apply to them the recently-developed HanleRT Tenerife Inversion Code, which assumes a one-dimensional model atmosphere for each spatial pixel under consideration (i.e., it neglects the effects of horizontal radiative transfer). We find that the non-magnetic causes of symmetry breaking, due to the horizontal inhomogeneities and the gradients of the horizontal components of the macroscopic velocity in the solar atmosphere, have a significant impact on the linear polarization profiles. By introducing such non-magnetic causes of symmetry breaking as parameters in our inversion code, we can successfully fit the Stokes profiles and provide an estimation of the magnetic field vector. For example, in the quiet region pixels, where no circular polarization signal is detected, we find that the magnetic field strength in the upper chromosphere varies between 1 and 20 gauss.

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arXiv2024

Mapping the longitudinal magnetic field in the atmosphere of an active region plage from the inversion of the near-ultraviolet CLASP2.1 spectropolarimetric data

We apply the HanleRT Tenerife Inversion Code to the spectro-polarimetric observations obtained by the Chromospheric LAyer SpectroPolarimeter. This suborbital space experiment measured the variation with wavelength of the four Stokes parameters in the near-ultraviolet spectral region of the Mg II h & k lines over a solar disk area containing part of an active region plage and the edge of a sunspot penumbra. We infer the stratification of the temperature, the electron density, the line of-sight velocity, the micro-turbulent velocity, and the longitudinal component of the magnetic field from the observed intensity and circular polarization profiles. The inferred model atmosphere shows larger temperature and electron density in the plage and the superpenumbra regions than in the quiet regions. The shape of the plage region in terms of its brightness is similar to the pattern of the inferred longitudinal component of the magnetic field in the chromosphere, as well as to that of the overlying moss observed by AIA in the 171 A band, which suggests a similar magnetic origin for the heating in both the plage and the moss region. Moreover, this heating is particularly significant in the regions with larger inferred magnetic flux. In contrast, in the superpenumbra, the regions with larger electron density and temperature are usually found in between these regions with larger magnetic flux, suggesting that the details of the heating mechanism in the chromosphere of the superpenumbra may be different to those in the plage, but with the magnetic field still playing a key role.

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arXiv2024

Magnetic field diagnostics of prominences with the Mg II k line: 3D Stokes inversions versus traditional methods

The Mg II k resonance line is commonly used for diagnosing the solar chromosphere. We theoretically investigated its intensity and polarization in solar prominences, taking 3D radiative transfer and Hanle and Zeeman effects into account. We used an optically thick 3D model representative of a solar prominence and applied several inversion methods to the synthetic Stokes profiles, clarifying their pros and cons for inferring prominence magnetic fields. We conclude that the self-consistent 3D inversion with radiative transfer is necessary to determine the magnetic field vector, although its geometry cannot be inferred with full fidelity. We also demonstrate that more traditional methods, such as those based on the weak field approximation or the constant-property slab assumption, can offer useful information under certain conditions.

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arXiv2024

Accurate PRD modeling of the forward-scattering Hanle effect in the chromospheric CaI 4227 Å line

Measurable linear scattering polarization signals have been predicted and detected at the solar disk center in the core of chromospheric lines. These forward-scattering polarization signals, which are of high interest for magnetic field diagnostics, have always been modeled either under the assumption of complete frequency redistribution (CRD), or taking partial frequency redistribution (PRD) effects into account under the angle-averaged (AA) approximation. This work aims at assessing the suitability of the CRD and PRD-AA approximations for modeling the forward-scattering polarization signals produced by the presence of an inclined magnetic field, the so-called forward-scattering Hanle effect, in the chromospheric CaI 4227 A line. Radiative transfer calculations are performed in semi-empirical 1D solar atmospheres, out of local thermodynamic equilibrium (LTE). A two-step solution strategy is applied: the non-LTE RT problem is first solved considering a multilevel atom and neglecting polarization phenomena. The same problem is then solved including polarization, considering a two-level atom and keeping fixed the lower-level population calculated at the previous step. The emergent linear polarization signals calculated under the CRD and PRD-AA approximations are analyzed and compared to those obtained by modeling PRD effects in their general angle-dependent (AD) formulation. With respect to the PRD-AD case, the CRD and PRD-AA calculations significantly underestimate the amplitude of the line-center polarization signals produced by the forward-scattering Hanle effect. The results of this work suggest that a PRD-AD modeling is required in order to develop reliable diagnostic techniques exploiting the forward-scattering polarization signals observed in the CaI 4227 A line. These results need to be confirmed by full 3D calculations including non-magnetic symmetry-breaking effects.

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arXiv2024

Observation and Modeling of the circular polarization of the Cr I magnetic field induced transition at 533.03 nm

We study the circular polarization of the magnetic field induced transition (MIT) between the $3d^5(^6S)4d\ ^7D_2$ and $3d^5(^6S)4p\ ^7P_4^\circ$ states of \ion{Cr}{1} at 533.03~nm (wavelength in air). The fractional circular polarization $V/I$ of this spectral line resulting from the solution of the radiation transfer problem in a sunspot model permeated by a homogeneous magnetic field of 3~kG shows amplitudes of about $2\%$. Spectro-polarimetric observations of two sunspots were obtained with the Zurich Imaging Polarimeter-3 at the Istituto ricerche solari Aldo e Cele Daccò (IRSOL) observatory observatory in Locarno, Switzerland. The observed $V/I$ profiles show approximately anti-symmetrical shapes with an amplitude of around $0.1\%$ and $0.2\%$ for the two sunspots. The center of this profile coincides with the wavelengths predicted for the above-mentioned MIT. We apply an inversion code to the spectro-polarimetric data of the \ion{Cr}{1} permitted lines at 532.91 and 532.98~nm, as well as to the MIT line at 533.03~nm, to infer a stratification of the emitting atmosphere. We compare the $V/I$ profiles synthesized in the inferred atmosphere models with the observations, showing that the observed signal likely corresponds to the MIT line.

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arXiv2024

Comparing Observed with Simulated Solar Disk Center Scattering Polarization in the Sr I 4607 Å line

Solar magnetic fields alter scattering polarization in spectral lines like Sr I at 4607 Å via the Hanle effect, making it a potential diagnostic for small-scale mixed-polarity photospheric magnetic fields. Recently, observational evidence for scattering polarization in the Sr I 4607 Å at the solar disk center was found. Here, we investigate the reliability of the reconstruction method making possible this detection. To this end, we apply it to linear polarization profiles of the Sr I 4607 Å line radiation emerging at the disk center obtained from a detailed 3D radiative transfer calculation in a magneto-hydrodynamic simulation snapshot with a small-scale dynamo contribution. The reconstruction method systematically reduces the scattering amplitudes by up to a factor of two, depending on the noise level. We demonstrate that the decrease can be attributed to two systematic errors: first, the physical constraint that underlies our assumptions regarding the dependence of scattering polarization on the quadrupolar moment of the radiation field, and second, the limitations of our method in accurately determining the sign of the radiation field tensor from the observed intensity image. However, consistently applying the reconstruction process and after taking into account image degradation effects due to the temporally variable image quality, such as imposed by seeing, observed and synthesized polarization signals show remarkable agreement. We thus conclude that the observed scattering polarization at solar disk center is consistent with that emerging from magneto-hydrodynamic model of the solar photosphere with an average magnetic field of 170 G at the visible surface.

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arXiv2023

The impact of angle-dependent partial frequency redistribution on the scattering polarization of the solar Na i D lines

The long-standing paradox of the linear polarization signal of the Na i D1 line was recently resolved by accounting for the atom's hyperfine structure and the detailed spectral structure of the incident radiation field. That modeling relied on the simplifying angle-averaged (AA) approximation for partial frequency redistribution (PRD) in scattering, which potentially neglects important angle-frequency couplings. This work aims at evaluating the suitability of a PRD-AA modeling for the D1 and D2 lines through comparisons with general angle-dependent (AD) PRD calculations, both in the absence and presence of magnetic fields. We solved the radiative transfer problem for polarized radiation in a one-dimensional semi-empirical atmospheric model with microturbulent and isotropic magnetic fields, accounting for PRD effects, comparing PRD-AA and PRD-AD modelings. The D1 and D2 lines are modeled separately as two-level atomic system with hyperfine structure. The numerical results confirm that a spectrally structured radiation field induces linear polarization in the D1 line. However, the PRD-AA approximation greatly impacts the Q/I shape, producing an antisymmetric pattern instead of the more symmetric PRD-AD one, while presenting a similar sensitivity to magnetic fields between 10 and 200 G. Under the PRD-AA approximation, the Q/I profile of the D2 line presents an artificial dip in its core, which is not found for the PRD-AD case. We conclude that accounting for PRD-AD effects is essential to suitably model the scattering polarization of the Na i D lines. These results bring us closer to exploiting the full diagnostic potential of these lines for the elusive chromospheric magnetic fields.

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arXiv2023

Magnetic field information in the near-ultraviolet Fe II lines of the CLASP2 space experiment

We investigate theoretically the circular polarization signals induced by the Zeeman effect in the Fe II lines of the 279.3-280.7 nm spectral range of the CLASP2 space experiment and their suitability to infer solar magnetic fields. To this end, we use a comprehensive Fe II atomic model to solve the problem of the generation and transfer of polarized radiation in semi-empirical models of the solar atmosphere, comparing the region of formation of the Fe II spectral lines with those of the Mg II h and k and the Mn I resonance lines. These are present in the same near ultraviolet (near-UV) spectral region and allowed the mapping of the longitudinal component of the magnetic field ($B_{\rm L}$) through several layers of the solar chromosphere in an active region plage. We compare our synthetic intensity profiles with observations from the IRIS and CLASP2 missions, proving the suitability of our model atom to characterize these Fe II spectral lines. The CLASP2 observations show two Fe II spectral lines at 279.79 and 280.66 nm with significant circular polarization signals. We demonstrate the suitability of the Weak-Field Approximation (WFA) applied to the Stokes $I$ and $V$ profiles of these Fe II lines to infer $B_{\rm L}$ in the plage atmosphere. We conclude that the near-UV spectral region of CLASP2 allows to determine $B_{\rm L}$ from the upper photosphere to the top of the chromosphere of active region plages.

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arXiv2023

The magnetic sensitivity of the (250-278nm) Fe II polarization spectrum

This paper presents a theoretical investigation on the polarization and magnetic sensitivity of the near-ultraviolet (near-UV) solar spectral lines of Fe II between 250 and 278 nm. In recent years, UV spectropolarimetry has become key to uncover the magnetism of the upper layers of the solar chromosphere. The unprecedented data obtained by the CLASP2 suborbital space experiment across the Mg II h and k lines around 280 nm are a clear example of the capabilities of near-UV spectropolarimetry for the magnetic field diagnostics throughout the whole solar chromosphere. Recent works have pointed out the possible complementary diagnostic potential of the many Fe II lines in the unexplored spectral region between 250 and 278 nm, but no quantitative analysis of the polarization and magnetic sensitivity of those spectral lines has been carried out yet. To study the polarization signals in these spectral lines, we create a comprehensive atomic model including all the atomic transitions resulting in strong spectral lines. We then study the magnetic sensitivity of the linear and circular polarization profiles in a semi-empirical model representative of the quiet sun. We present a selection of Fe II spectral lines with significant linear and circular polarization signals and evaluate their diagnostic capabilities by studying their formation heights and magnetic sensitivity through the action of the Hanle and Zeeman effects. We conclude that when combined with the CLASP2 spectral region these Fe II lines are of interest for the inference of magnetic fields throughout the solar chromosphere, up to near the base of the corona.

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arXiv2023

Evidence for the Operation of the Hanle and Magneto-Optical Effects in the Scattering Polarization Signals Observed by CLASP2 Across the Mg II h and k Lines

Radiative transfer investigations of the solar Mg II h and k resonance lines around 280~nm showed that, while their circular polarization (Stokes V) signals arise from the Zeeman effect, the linear polarization profiles (Stokes Q and U) are dominated by the scattering of anisotropic radiation and the Hanle and magneto-optical (MO) effects. Using the unprecedented observations of the Mg II and Mn I resonance lines obtained by the Chromospheric LAyer Spectro-Polarimeter (CLASP2), here we investigate how the linear polarization signals at different wavelengths (i.e., at the center, and at the near and far wings of the k line) vary with the longitudinal component of the magnetic field ($B_{L}$) at their approximate height of formation. The $B_{L}$ is estimated from the V signals in the aforementioned spectral lines. Particular attention is given to the following quantities that are expected to be influenced by the presence of magnetic fields through the Hanle and MO effects: the sign of the U signals, the total linear polarization amplitude ($LP$) and its direction ($χ$) with respect to a reference direction. We find that at the center and near wings of the $k$ line, the behavior of these quantities is significantly different in the observed quiet and plage regions, and that both $LP$ and $χ$ seem to depend on $B_{L}$. These observational results are indicative of the operation of the Hanle effect

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