Chromospheric polarimetry through multi-line observations of the 850 nm spectral region

Future solar missions and ground-based telescopes aim to understand the magnetism of the solar chromosphere. We performed a supporting study in Quintero Noda et al. (2016) focused on the infrared Ca II 8542 A line and we concluded that is one of the best candidates because it is sensitive to a large range of atmospheric heights, from the photosphere to the middle chromosphere. However, we believe that it is worth to try improving the results produced by this line observing additional spectral lines. In that regard, we examined the neighbour solar spectrum looking for spectral lines that could increase the sensitivity to the atmospheric parameters. Interestingly, we discovered several photospheric lines that greatly improve the photospheric sensitivity to the magnetic field vector. Moreover, they are located close to a second chromospheric line that also belongs to the Ca II infrared triplet, i.e. the Ca II 8498 A line, and enhances the sensitivity to the atmospheric parameters at chromospheric layers. We conclude that the lines in the vicinity of the Ca II 8542 A line not only increase its sensitivity to the atmospheric parameters at all layers, but also they constitute an excellent spectral window for chromospheric polarimetry.Comment: 11 pages, 8 figures, 1 tabl

Solar polarimetry through the K I lines at 770 nm

We characterize the K I D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca II infrared triplet lines and several Zeeman sensitive photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in different atmospheric parameters, and the spatial distribution of Zeeman polarization signals employing a realistic magnetohydrodynamic simulation. The results show that these lines form in the upper photosphere at around 500 km and that they are sensitive to the line of sight velocity and magnetic field strength at heights where neither the photospheric lines nor the Ca II infrared lines are. However, at the same time, we found that their sensitivity to the temperature essentially comes from the photosphere. Then, we conclude that the K I lines provide a complement to the lines in the 850 nm window for the determination of atmospheric parameters in the upper photosphere, especially for the line of sight velocity and the magnetic field.Comment: 10 pages, 9 figures, main journal publicatio

Study of the polarization produced by the Zeeman effect in the solar Mg I b lines

The next generation of solar observatories aim to understand the magnetism of the solar chromosphere. Therefore, it is crucial to understand the polarimetric signatures of chromospheric spectral lines. For this purpose, we here examine the suitability of the three Fraunhofer Mg I b1, b2, and b4 lines at 5183.6, 5172.7, and 5167.3 A, respectively. We start by describing a simplified atomic model of only 6 levels and 3 line transitions for computing the atomic populations of the 3p-4s (multiplet number 2) levels involved in the Mg I b line transitions assuming non-local thermodynamic conditions and considering only the Zeeman effect using the field-free approximation. We test this simplified atom against more complex ones finding that, although there are differences in the computed profiles, they are small compared with the advantages provided by the simple atom in terms of speed and robustness. After comparing the three Mg I lines, we conclude that the most capable one is the b2 line as b1 forms at similar heights and always show weaker polarization signals while b4 is severely blended with photospheric lines. We also compare Mg I b2 with the K I D1 and Ca II 8542 A lines finding that the former is sensitive to the atmospheric parameters at heights that are in between those covered by the latter two lines. This makes Mg I b2 an excellent candidate for future multi-line observations that aim to seamlessly infer the thermal and magnetic properties of different features in the lower solar atmosphere.Comment: 14 pages, 11 figures, and 5 table

Chromospheric polarimetry through multi-line observations of the 850 nm spectral region II: A magnetic flux tube scenario

In this publication we continue the work started in Quintero Noda et al. (2017) examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the physical phenomena that take place in it, in particular, the magnetic pumping, leaves a specific imprint on the examined spectral lines. We find that the profiles from the interior of the flux tube are periodically dopplershifted following an oscillation pattern that is also reflected in the amplitude of the circular polarization signals. In addition, we analyse the properties of the Stokes profiles at the edges of the flux tube discovering the presence of linear polarization signals for the Ca II lines, although they are weak with an amplitude around 0.5% of the continuum intensity. Finally, we compute the response functions to perturbations in the longitudinal field and we estimate the field strength using the weak field approximation. Our results indicate that the height of formation of the spectral lines changes during the magnetic pumping process which makes the interpretation of the inferred magnetic field strength and its evolution more difficult. These results complement those from previous works demonstrating the capabilities and limitations of the 850 nm spectrum for chromospheric Zeeman polarimetry in a very dynamic and complex atmosphere.Comment: 12 pages, 12 figures, 0 tables, MNRAS main journal publicatio

Chromospheric polarimetry through multi-line observations of the 850 nm spectral region III: Chromospheric jets driven by twisted magnetic fields

We investigate the diagnostic potential of the spectral lines at 850 nm for understanding the magnetism of the lower atmosphere. For that purpose, we use a newly developed 3D simulation of a chromospheric jet to check the sensitivity of the spectral lines to this phenomenon as well as our ability to infer the atmospheric information through spectropolarimetric inversions of noisy synthetic data. We start comparing the benefits of inverting the entire spectrum at 850 nm versus only the Ca II 8542 A spectral line. We found a better match of the input atmosphere for the former case, mainly at lower heights. However, the results at higher layers were not accurate. After several tests, we determined that we need to weight more the chromospheric lines than the photospheric ones in the computation of the goodness of the fit. The new inversion configuration allows us to obtain better fits and consequently more accurate physical parameters. Therefore, to extract the most from multi-line inversions, a proper set of weights needs to be estimated. Besides that, we conclude again that the lines at 850 nm, or a similar arrangement with Ca II 8542 A plus Zeeman sensitive photospheric lines, poses the best observing configuration for examining the thermal and magnetic properties of the lower solar atmosphere.Comment: 14 pages, 11 figure

Increasing the Fine Structure Visibility of the Hinode SOT Ca II H Filtergrams

We present the improved so-called Madmax (OMC) operator selecting maxima of convexities computed in multiple directions around each pixel rewritten in MatLab and shown to be very efficient for pattern recognition. The aim of the algorithm is to trace the bright hair-like features (for ex. chromospheric thin jets or spicules) of solar ultimate observations polluted by a noise of different origins. This popular spatial operator uses the second derivative in the optimally selected direction for which its absolute value has a maximum value. Accordingly, it uses the positivity of the resulting intensity signal affected by a superposed noise. The results are illustrated using a test artificially generated image and real SOT (Hinode) images are also used, to make your own choice of the sensitive parameters to use in improving the visibility of images.Comment: 12 pages, 3 figurs, submitted in Solar Physic

Study of the polarization produced by the Zeeman effect in the solar MgI b lines

The next generation of solar observatories aim to understand the magnetism of the solar chromosphere. Therefore, it is crucial to understand the polarimetric signatures of chromospheric spectral lines. For this purpose, we here examine the suitability of the three Fraunhofer MgI b1, b2, and b4 lines at 5183.6, 5172.7, and 5167.3 Å, respectively. We start by describing a simplified atomic model of only six levels and three line transitions for computing the atomic populations of the 3p-4s (multiplet number 2) levels involved in the Mg I b line transitions assuming non-local thermodynamic conditions and considering only the Zeeman effect using the field-free approximation. We test this simplified atom against more complex ones finding that, although there are differences in the computed profiles, they are small compared with the advantages provided by the simple atom in terms of speed and robustness. After comparing the three MgI lines, we conclude that the most capable one is the b2 line as b1 forms at similar heights and always shows weaker polarization signals, while b4 is severely blended with photospheric lines. We also compare Mg I b2 with the KI D1 and Ca II 8542 Å lines finding that the former is sensitive to the atmospheric parameters at heights that are in between those covered by the latter two lines. This makes MgI b2 an excellent candidate for future multiline observations that aim to seamlessly infer the thermal and magnetic properties of different features in the lower solar atmosphere. © 2018 The Author(s).We appreciate the help of the anonymous referee that, during the revision process, provided us comments and suggestions that allowed improving the manuscript. CQN acknowledges the support of the ISAS/JAXA International Top Young Fellowship and the JSPS KAKENHI grant number 18K13596. The SUNRISE-3 project is supported in Japan by the funding from ISAS/JAXA for the smallscale program for novel solar observations and the JSPS KAKENHI grant numbers 18H03723 and 18H05234. This research was supported by the Research Council of Norway through its Centres of Excellence scheme, project number 262622. This work has also been supported by Spanish Ministry of Economy and Competitiveness through the project ESP-2016-77548-C5-1-R. DOS also acknowledges financial support through the Ramon y Cajal fellowships

A Study of the PDGF Signaling Pathway with PRISM

In this paper, we apply the probabilistic model checker PRISM to the analysis of a biological system -- the Platelet-Derived Growth Factor (PDGF) signaling pathway, demonstrating in detail how this pathway can be analyzed in PRISM. We show that quantitative verification can yield a better understanding of the PDGF signaling pathway.Comment: In Proceedings CompMod 2011, arXiv:1109.104