Ministerio de Economía y Competitividad Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

Astrophysics Research Projects

The Sun and Solar System

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Magnetism, Polarization and Radiative Transfer in Astrophysics (P/300725)

J TRUJILLO BUENO

Andrés Asensio Ramos, Fernando Moreno Insertis, Héctor Socas Navarro, Ernest Alsina Ballester, Ana Belén Griñón Marín, Melania Cubas Armas, Nikolas Vitas, Reza Rezaei

Colaboradores del IAC: María Jesús Martínez González, Iñigo Arregui Uribe-Echevarria, Cristina Ramos Almeida, Carlos Allende Prieto, Manuel Collados Vera, Basilio Ruiz Cobo

M. Bianda, R. Ramelli, L. Belluzzi (Istituto Solari Ricerche); R. Casini, R. Centeno, J. Cernicharo (CAB, Spain); J. de la Cruz (University of Stockholm); E. Landi Degl'Innocenti (Univ. Florencia); N. Shchukina (Main Astronomical Observatory; Kiev); H. Uitenbroek (NSO); D. Mckenzie (University of Alabama); R. Ishikawa, R. Kano (NAOJ); J. Stepan (Astronomical Institute Czech Republic)

Introduction

Magnetic fields pervade all astrophysical plasmas and govern most of the variability in the Universe at intermediate time scales. They are present in stars across the whole Hertzsprung-Russell diagram, in galaxies, and even perhaps in the intergalactic medium. Polarized light provides the most reliable source of information at our disposal for the remote sensing of astrophysical magnetic fields, including those on the Sun. In particular, the diagnostics of solar and stellar magnetic fields requires the measurement and physical interpretation of polarization signatures in spectral lines, which are induced by various physical mechanisms taking place at the atomic level. In addition to the familiar Zeeman effect, polarization can also be generated by various other physical processes, such as atomic level polarization induced by anisotropic pumping mechanisms, quantum interferences between fine-structured or hyperfine-structured energy levels, the Hanle effect, etc. Interestingly, the polarization produced by such mechanisms is sensitive to the physical conditions of the astrophysical plasma under consideration and, in particular, to the presence of magnetic fields in a parameter domain that goes from field intensities as small as 1 micro-G to many thousands of Gauss.

The main aim of this project is to explore in depth the physics and origin of polarized radiation in astrophysical plasmas as well as its diagnostic use for understanding cosmical magnetic fields, with emphasis on the magnetism of the extended solar atmosphere. Our investigations deal with:

- the theoretical understanding of relevant polarization physics, which requires new insights into the quantum theory of polarized light scattering in the presence of magnetic and electric fields.

- the development of plasma diagnostic tools for the investigation of astrophysical magnetic fields, with emphasis on the magnetism of the extended solar atmosphere, circumstellar envelopes and planetary nebulae.

- spectropolarimetric observations and their physical interpretation.

- radiative transfer in three-dimensional models of stellar atmospheres, resulting from magneto-hydrodynamical simulations.

- atomic and molecular spectroscopy and spectro-polarimetry, with applications in several fields of astrophysics.

This research project is formed by a group of scientists convinced of the importance of complementing theoretical and observational investigations in order to face some of the present challenges of 21st century Astrophysics.

Milestones

Investigations on the thermal, dynamic and magnetic structure of several solar plasma structures, like sunspots, penumbrae, light bridges and the quiet Sun.

Demonstration that it is possible to measure polarization with a polarimeter in spite of measuring at frequencies well below the seeing variations with a slow camera.

Development of a radiative transfer code that takes into account Partial Frequency Redistribution (PRD) and the joint action of the Hanle and Zeeman effects. Its application has allowed to discover a new physical mechanism that introduces an interesting magnetic sensitivity in the wings of the linear polarization profiles of strong chromospheric lines, such as the Mg II k line.

Extension of the group's inversion codes, which will improve further the interpretation of spectro-polarimetric observations.

The interpretation with our code HAZEL of observations of active region filaments has led to a new model with two atmospheric components along the line of sight.

The inversions suggest that one component has hG magnetic fields and the other very week fields.

Improvement of the NICOLE inversion and synthesis code, which is being used by various groups worldwide.

Novel studies on the solar chemical abundances.

Analysis of HMI data which sheds light on a new dynamical phenomenon in the penumbrae of sunspots.

Development of a NLTE inversion code taking into account PRD effects.

Applications of our PORTA radiative transfer code for doing, with the MareNostrum supercomputer, novel investigations on the generation and transfer of polarized radiation in the IR triplet of Ca II using 3D models of the solar chromosphere resulting from MHD simulations.

In collaboration with groups in Japan, USA and Europe, preparation and submission to NASA of the CLASP-2 sounding rocket project, in order to measure the polarization caused by the joint action of the Hanle and Zeeman effects in the Mg II h & k lines around 2800 Angstroms. This project was accepted for funding by NASA in December 2016. Its launch is foreseen for 2019.

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