Optical tomography of a sunspot. Three-dimensional structure of the magnetic field strength. Only three layers of given optical depths are displayed.

Small area of 148”x74” showing the magnetic field strengths (top) and inclinations (middle) inferred from the inversion. Network and internetwork areas can be easily identified. Black areas correspond to noninverted pixels. The field strength color bar has been clipped at 1000 G (white).

Internal structure of the Sun, planetary torque, and the solar tachocline.

During the last five years, the scientific activities of the group have focused on the study and characterization of the sunspot and quiet Sun magnetic fields through spectroscopic and spectropolarimetric measurements with high spatial and temporal resolution. One of the main objectives of this period has been the analysis of the evolution of sunspot penumbrae magnetic field evolution and the emergence processes in the quiet Sun. The intensification mechanisms of the magnetic field in network elements have been studied as well. Likewise, studies about the solar atmosphere coupling through magnetic flux cancellation in the surroundings of sunspots have started.

More theoretical works have been carried out in parallel about radiative transfer of polarized light in stellar atmospheres in order to develop new tools that allow us to accurately retrieve the physical properties of solar plasma. In this context, we have investigated the sensitivity of spectral lines to the various atmospheric parameters and analytic expressions have been obtained for the response functions of Stokes profiles in Milne-Eddington atmospheres. Magnetohydrodynamic studies of flux tube storage have been carried out, as well as analysis of the origin of the solar cycle and qualitative analysis on polarity changes of the Earth's magnetic field. We have developed two inversion codes of the radiative transfer equation. The MILOS code implements a Milne-Eddington, one-component model atmosphere. The SIRJUMP code is able to deal with sharp discontinuities in the stratification of atmospheric parameters. Both codes are being successfully used for the analysis of observations with the Hinode satellite. Recently, we have opened a new line of research for the development of numerical tools necessary for building an electronic inverter of the radiative transfer equation, based on FPGA (Field Programmable Gate Array) devices. This electronic inverter will fly in the ESA’s Solar Orbiter mission, being in charge of the on-board scientific data analysis for the PHI (Polarimetric and Helioseismic Imager) instrument.

Last, but not least, several theoretical studies about the variability of the solar irradiance and about the structure and instabilities of solar flux tubes have been carried out as well.

INSTRUMENTAL ACTIVITIES

The Solar Physics Group at IAA is involved in the design and development of state-of-the-art solar instrumentation for both ground-based and (balloon-) space-borne telescopes. We have built, together with the Kiepenheuer-Institut für Sonnenphysik (KIS, Freiburg, Germany), the Visible Imaging Polarimeter (VIP), a polarimeter based on liquid crystals variable retarders for the TESOS spectrometer operating at the Vacuum Tower Telescope (Observatorio del Teide).

The SPG has participated in the scientific and technical definition of the Imaging Magnetograph eXperiment (IMaX) that flew in June, 2009 and in June, 2013 within the stratospheric balloon mission Sunrise. Our group was responsible of the whole electronics and control software for IMaX. The instrument was made by a Spanish consortium including the Instituto de Astrofísica de Canarias (IAC, La Laguna, Tenerife), the Instituto Nacional de Técnica Aeroespacial (INTA, Torrejón de Ardoz, Madrid), and the Grupo de Astronomía y Ciencias del Espacio (GACE, Universidad de Valencia). Our group currently leads the IMaX consortium.

We participate as co-PI institution in the development of the PHI instrument for the ESA’s Solar Orbiter mission, together with the Max Plank Institut für Sonnensystem-forschung (MPS, Göttingen, Germany). The international consortium also includes the KIS, the Institut für Datentechnik und Kommuni-kationsnetze (IDA, Braunschweig, Germany), the Institut d’Astrophysque Spatiale (IAS, Orsay, France), the IAC, the INTA, the GACE, the Instituto Ignacio da Riva (IDR, Universidad Politécnica de Madrid), and the Universitat de Barcelona (UB). We are responsible for the electronic box and harness and for the electronic inverter of the instrument and contribute to the definition of scientific requirements and the techniques that will be employed for data analysis.

OBSERVATIONAL ACTIVITIES 

The SPG at IAA conducts one or two observational campaigns per year in average using several ground-based telescopes. Such a performance led us to participate in fairly significant achievements, namely, the first spectropolarimetric observations simultaneously in the visible and the near infrared (obtained at the Vacuum Tower Telescope of the Observatorio del Teide) and the first spectroscopic observations at a spatial resolution of 0.2 arcsec (obtained with the New Swedish one-meter Solar Tower of the Observatorio de El Roque de los Muchachos). The team members have expertise in several observational techniques like imaging, spectroscopy, and spectropolarimetry, both with Fabry-Pérot interferometers and with slit spectrographs. The group maintains close collaboration with the Japanese researchers of the Hinode mission. Several scientific exchanges have been made with the National Astronomical Observatory of Japan and the University of Kyoto during the last years. Moreover, we belong to the Science Working Group of the mission. This ensures our access to satellite observing time, either through open calls or collaboration with the Japanese scientists.

Finally, our participation in the IMaX instrument, enables the group to use the very high spatial resolution polarimetric measurements made with it during its two stratospheric flights. After a long and difficult data reduction and analysis process, the observations are being exploited scientifically.