María Jesús Martínez González, María Montes Solis, Elena Khomenko, Iñigo Arregui Uribe-Echevarria, Basilio Ruiz Cobo, Manuel Collados Vera, Andrés Asensio Ramos, Carlos Westendorp Plaza, Carlos José Díaz Baso, Juan Carlos Trelles Arjona
IAC Collaborators: Héctor Socas Navarro, Manuel Luna Bennasar, Ana Belén Griñón Marín
R. Bellot Rubio, J.C. del Toro Iniesta (IAA, Granada); R. Kostik, N. Shchukina (Main Astronomical Observatory, Ucrania); V. Olshevsky (Katholic Univ. Leuven, Bélgica); A. Sainz Dalda (Stanford University, EEUU); W. Schmidt, D. Soltau, Th. Berkefeld, S.K. Solanki, A. Gandorfer (MPI fur Sonnesystemforschung, Alemania); P. Cally, S. Shelyag (Monash Univ. Melbourne, Australia); M. Stangalini (Univ. Tor Vergata, Italia); C. Beck (National Solar Observatory, EEUU); C. Kuckein (Astronomical Institut Potsdam, Alemania); C. Quintero Noda (Japan Aerospace Exploration Agency, Japón); I. Calvo Santamatia (Katholic University, Bélgica); Carlos González Fernández (Cambridge University, RU); Jaime de la Cruz Rodríguez (Stockholm University, Secia); Martin Leitzinger (Graz University, Austria); Adur Pastor Yabar (Kiepenheuer Institute for Solar Physics, Alemania); Arturo López Ariste (CNRS, Francia); Franco Leone (Universidad de Catania, Italia); Rafael Manso Sainz (Max Planck Institute for Solar System Research, Alemania)
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 mollecular 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.
Numerical simulations of quiet Sun magnetic fields seeded by the Biermann battery
Khomenko, E., Vitas, N., Collados, M., de Vicente, A. 2017, A&A, 604, 66
The magnetic fields of the quiet Sun cover at any time more than 90% of its surface and their magnetic energy budget is crucial to explain the thermal structure of the solar atmosphere. One of the possible origins of these fields is the action of the local dynamo in the upper convection zone of the Sun. Existing simulations of the local solar dynamo require an initial seed field and sufficiently high spatial resolution in order to achieve the amplification of the seed field to the observed values in the quiet Sun. In this work, we report an alternative model of seeding based on the action of the Bierman battery effect. This effect generates a magnetic field due to the local imbalances in electron pressure in the partially ionized solar plasma. We show that the battery effect self-consistently creates from zero an initial seed field of a strength of the order of micro G, and together with dynamo amplification allows the generation of quiet Sun magnetic fields of a similar strength to those from solar observations.
DeepVel: Deep learning for the estimation of horizontal velocities at the solar surface
Asensio Ramos, A., Requerey, I. S., Vitas, N. 2017, A&A, 604, 11
Many phenomena taking place in the solar photosphere are controlled by plasma motions. Although the line-of-sight component of the velocity can be estimated using the Doppler effect, we do not have direct spectroscopic access to the components that are perpendicular to the line of sight. These components are typically estimated using methods based on local correlation tracking. We have designed DeepVel, an end-to-end deep neural network that produces an estimation of the velocity at every single pixel, every time step, and at three different heights in the atmosphere from just two consecutive continuum images. We confront DeepVel with local correlation tracking, pointing out that they give very similar results in the time and spatially averaged cases. We use the network to study the evolution in height of the horizontal velocity field in fragmenting granules, supporting the buoyancy-braking mechanism for the formation of integranular lanes in these granules. We also show that DeepVel can capture very small vortices, so that we can potentially expand the scaling cascade of vortices to very small sizes and durations.