Fernando Moreno Insertis, Javier Trujillo Bueno, Elena Khomenko, Iñigo Arregui Uribe-Echevarria, Beatrice Popescu Brailenau, Valeriia Liakh, Nikolas Vitas, Daniel E. Nóbrega Siverio, Ángel de Vicente Garrido, Tobias Felipe García, Pedro A. González Morales
K. Galsgaard (Niels Bohr Institute/Univ Copenhague), J. Martínez Sykora (Lockheed Martin Solar and Astrophysical Laboratory), V. Hansteen (Univ. Oslo); E. Priest (Univ St Andrews), N. Shchukina (Obs. Kiev); J. Stepan (Astronomical Institute ASCR, Ondrejov), Maria Madjarska (Max Planck Institute for Solar System Research, Gottingen), L. Belluzzi (Obs Locarno), T. del Pino (HAO), V. Olshevsky (Katholic Univ. Leuven); P. Cally, S. Shelyag (Monash Univ. Melbourne); M. Stangalini (Univ. Tor Vergata, Roma), I. Calvo Santamaria (Katholieke Univ. Leuven), J. Klimchuk (NASA Goddard); T. Kucera, K. Muglach, H. Gilbert, J. Karpen (NASA Goddard Space Flight Center), B. Schmieder (LESIA, Paris), Dr. Ramesh Chandra (Kumaun University, Nainita).
The general aim of this project is the investigation of astrophysical processes through the use of state-of-the-art numerical codes on massively parallel computers. More specifically, the research in many astrophysical fields requires understanding of gas dynamical, magnetic, radiative transfer and gravitational phenomena phenomena not accessible to purely theoretical analysis. In the framework of this project calculations aimed at understanding the multidimensional structure and evolution of magnetic fields in stellar atmospheres and interiors are carried out, including magnetohydrodynamical aspects, radiative transfer and spectral line polarization. Special emphasis is placed on the comparison of the theoretical/numerical results with observational data.
1.- Solar surges are ejective episodes detected in the low atmosphere often related to the emergence of magnetized plasma from the solar interior. Traditionally, they have been observed in chromospheric lines such as Hα 6563 A and Ca II 8542 A. However, whether there is a response to the surge appearance and evolution in transition region lines, like Si IV 1402, had not been studied. Those lines are important to understand the periphery of the surges, as well as their origin and evolution. In our work, a simultaneous episode of appearance of an Hα surge and a Si IV burst has been analyzed that occurred on 2016 September 03 in active region AR 12585. We used coordinated observations from the Interface Region Imaging Spectrograph satellite (IRIS) and from the Swedish 1-m Solar Telescope installed on the Roque de los Muchachos Observatory in La Palma. In our work, the appearance of Si IV emission within the observed domain of the surge is reported for the first time, finding profiles that are brighter and broader than the average, having also identified the location of the brightest Si IV patches in the region near the surge's footpoints. To understand the relation between the surges and the emission in transition region lines like Si IV, we have carried out 2.5D radiative-MHD experiments of magnetic flux emergence episodes using the Bifrost code and including the nonequilibrium ionization of silicon. Through spectral synthesis of the model data, we could show that the presence of Si IV emission patches within the surge, their location near the surge footpoints and various observed spectral features are a natural consequence of the emergence of magnetized plasma from the interior to the atmosphere and the ensuing reconnection processes.
Fig.1 Si IV emission image (left) and image taken with the Hα filter (right) that show the simultaneous occurrence of a surge (dark regions in the right panel) and of Si IV brightenings. (A) Slit-jaw image (SJI) in the Si IV 1400 Å passband taken by the IRIS satellite. (B) SST/CRISP image in the blue wing the Hα line at −46 km / s. Bright regions in the SJI 1400 image are overplotted as green contours in the two panels, while the bright and dark structures of the Hα blue wing scan are superimposed in red and blue, respectively, to facilitate the identification. The arrows R1 and R2 point to the studied surge, and the SiIV burst, respectively. From Nóbrega-Siverio et al, 2017, ApJ 850, 153
2.- We follow the eruption of two related intermediate filaments observed in Hα (from GONG) and EUV (from Solar Dynamics Observatory SDO/Atmospheric Imaging assembly AIA; see Fig. 2(a)) and the resulting large-amplitude longitudinal oscillations of the plasma in the filament channels (Fig. 2(b)). The events occurred in and around the decayed active region AR12486 on 2016 January 26. Our detailed study of the oscillation reveals that the periods of the oscillations are about one hour. In Hα, the period decreases with time and exhibits strong damping. The analysis of 171 Å images shows that the oscillation has two phases: an initial long-period phase and a subsequent oscillation with a shorter period. In this wavelength, the damping appears weaker than in Hα. The velocity is the largest ever detected in a prominence oscillation, approximately 100 km/s (see Fig. 2(c). Using SDO/HMI magnetograms, we reconstruct the magnetic field of the filaments, modeled as flux ropes by using a flux-rope insertion method (see Fig. 2(d)). Applying seismological techniques, we determine that the radii of curvature of the field lines in which cool plasma is condensed are in the range 75-120 Mm, in agreement with the reconstructed field. In addition, we infer a field strength of ≥7 to 30 Gauss, depending on the electron density assumed, that is also in agreement with the values from the reconstruction (8-20 Gauss). The poloidal flux is zero and the axis flux is on the order of 1020 to 1021 Mx, confirming the high shear existing even in a non-active filament.
Fig. 2 In (a) the AIA image is shown in 171Å where the filament studied appears in absopción in the central part. S1, S2 and S3 indicate the artificial slits used to study the movement. In (b) the time-distance diagram of S1 is shown. In (c) the measured velocity that is perpendicular to the line of sight is shown. The large amplitude is shown with more than 100 km/s. In (d) the reconstructed magnetic field is shown that agrees with that obtained by seismology. From Luna et al., 2017, ApJ, 850, 143.