Elena Khomenko, Iñigo Arregui Uribe-Echevarria, María Montes Solís, Basilio Ruiz Cobo, Tobias Felipe García, Manuel Collados Vera, Andrés Asensio Ramos, Carlos Westendorp Plaza, Carlos José Díaz Baso
Colaboradores del IAC: Héctor Socas Navarro, Manuel Luna Bennasar, Ana Belén Griñón Marín
L.R. Bellot Rubio, J.C. del Toro Iniesta (IAA, Spain); R. Kostik, N. Shchukina (Main Astronomical Observatory); V. Olshevsky (Katholic Univ. Leuven); A. Sainz Dalda (Stanford University); W. Schmidt, D. Soltau, Th. Berkefeld, S.K. Solanki, A. Gandorfer (MPI fur Sonnesystemforschung); P. Cally, S. Shelyag (Monash Univ. Melbourne); M. Stangalini (Univ. Tor Vergata); C. Beck (National Solar Observatory); C. Kuckein (Astronomical Institut Potsdam); C. Quintero Noda (Japan Aerospace Exploration Agency); I. Calvo Santamaria (Katholic University); C. González Fernández (Cambridge University); J.de la Cruz Rodríguez (Stockholm University); M. Leitzinger (Graz University); A. Pastor Yabar (Kiepenheuer Institute for Solar Physics); A. López Ariste (CNRS); Franco Leone (Universidad de Catania); R. Manso Sainz (Max Planck Institute for Solar System Research)
Magnetic fields are at the base of star formation and stellar structure and evolution. When stars are born, magnetic fields brake the rotation during the collapse of the molecular cloud. In the end of the life of a star, magnetic fields can play a key role in the form of the strong winds that lead to the last stages of stellar evolution. During the whole adult life of a star, magnetic fields are the origin of stellar activity. Our Sun has magnetic fields that give rise to such spectacular activity that impacts the climate on Earth. The magnetic activity in other stars is, in some cases, of orders of magnitude more intense than the solar one, influencing – often drastically – the transport of chemical species and angular momentum, as well as affecting the possible planetary systems around them.
The aim of this project is the study of the diverse manifestations of the magnetic field that can be observed in the solar atmosphere and in other stars. These include distinct structures as sunspots, weak quiet-sun fields or chromospheric and coronal features such as filaments and prominences. The following research topics have been gradually faced:
1. Structure and evolution of Sunspot magnetic fields.
2. Structure and evolution of quiet Sun magnetic fields.
3. Structure and evolution of the magnetism of the chromosphere and of chromospheric structures (prominences, spicules,..)
4. Structure and evolution or coronal loops.
5. Structure and evolution of the Sun's global field. Studies of the activity cycle.
6. Empirical study of propagation of magnetohydrodynamic waves in magnetic structures.
7. Empirical study of energy transfer mechanisms related with the heating of the external atmospheric layers.
8. Empirical study of the influence of partial ionisation in the dynamics of the solar atmosphere. 9. Participation in the European Solar Telescope project.
1. Development of numerical tools to diagnose stellar magnetic fields, both in the surface and in the chromosphere.
2. Study of magnetic fields in stellar prominences.
3. Study of the role of magnetic fields in the late stages of stellar evolution.
1) Observational Detection of Drift Velocity between Ionized and Neutral Species in Solar Prominences. Lead author: Elena Khomenko
In this paper, the authors report the detection of differences in the ion and neutral velocities in prominences using high-resolution spectroscopy obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). This observational result is a confirmation that such non-ideal magnetohydrodynamical effects do take place in the upper solar atmosphere.
2) Inference of the chromospheric magnetic field orientation in the Ca II 8542 A line fibrils. Lead author: Andrés Asensio Ramos
In this study, the authors use a statistical approach to study if the magnetic field in the solar chromosphere is aligned with the fibrils visible in the intensity images of this layer. It is found that fibrils are often well aligned with the magnetic field azimuth. Despite this alignment, the analysis also shows that there is a non-negligible dispersion, especially in penumbral filaments.
3) Active region filaments might harbor weak magnetic fields. Lead author: Carlos José Díaz Baso
In this paper, we solve the apparent controversial results on the magnetism of active region filaments. Some works have suggested that the magnetic fields in these structures are strong (500-600 G), in contrast to the weak fields found in quiet region filaments (10 G). We show that with a two component model, which includes scattering polarisation, the observed profiles can be fitted assuming a strong field in the lower atmosphere of the filament, and a weak field in the upper layers.
4) Synthetic polarimetric spectra from stellar prominences. Lead author: Tobías Felipe
In this paper, the polarised spectrum coming from stellar prominences is synthesized. It is shown that, taking values of the parameters from observed cool star prominences, the polarisation signals are detectable using the MIRADAS instrument with integration times of few minutes. The numerical code has been made available to the community through the github platform.