Start year
2007
Organizational Unit
Organizing institutions
General
Description
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 interference 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 objective 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.
Members
Principal investigator
Tanausú del
Pino Alemán
Project staff
Andrés
Asensio Ramos
Javier
Trujillo Bueno
Héctor David
Socas Navarro
Nikola
Vitas
Andrii
Sukhorukov
Ángel Manuel de
Vicente Garrido
Fernando
Moreno Insertis
Supriya
Hebbur Dayananda
Sara
Esteban Pozuelo
Edgar Samuel
Carlín Ramírez
Collaborators
Carlos
Allende Prieto
Íñigo
Arregui Uribe-Echevarría
Cristina
Ramos Almeida
Dr.
M. Bianda
Dr.
R. Ramelli
Dr.
L. Belluzzi
Dr.
R. Casini
Dr.
R. Centeno
Dr.
J. de la Cruz
Dr.
N. Shchukina
Dr.
H. Uitenbroek
Dr.
D. Mckenzie
Dr.
R. Ishikawa
Basilio
Ruiz Cobo
María Jesús
Martínez González
Results
- We applied deep learning techniques to the analysis of observations. Using convolutional neural networks, we developed techniques for the deconvolution of observational data. These techniques were also used to accelerate the deconvolution process of ground-based observations, achieving a cadence of around a hundred images processed per second.
- We developed an inference technique based on bayesian statistics in order to interpret the observations provided by the CLASP international experiment. By parametrizing a state-of-the-art magneto-hydrodynamical model of the solar atmosphere, we found that the geometrical complexity of the transition region must be much more complex than the one provided by the model.
- We solved the problem of polarized radiation transfer in magneto-convection simulations that account for small-scale dynamo action for the Sr I line at 460.7 nm. We found that the model with most of the convection zone magnetized close to the equipartition and a surface mean field strength of 170G is compatible with the available observations.
- We studied the magnetic sensitivity of the Ca I line at 422.7nm. The linear polarization at the core is sensitive to the Hanle effect, while the linear polarization in the wings is sensitive to the magneto-optical effects, as a consequence of the newly found effect resulting from the joint action of partial redistribution and the Zeeman effects.
- We studied the formation of the H-alpha, Mg II h-k, and Ca II H-K and 845.2nm in a model atmosphere of a flaring bipolar active region, solving the radiation transfer problem taking into account partial redistribution in full 3D geometry and out of local thermodynamical equilibrium. We succeeded in reproducing common observational features of such flaring regions.
Scientific activity
Related publications
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Isotropic inelastic and superelastic collisional rates in a multiterm atomThe spectral line polarization of the radiation emerging from a magnetized astrophysical plasma depends on the state of the atoms within the medium, whose determination requires considering the interactions between the atoms and the magnetic field, between the atoms and photons (radiative transitions), and between the atoms and other materialTrujillo-Bueno, J. et al.
Advertised on:
32013 -
The Filling Factor-Radius Relation for 58 H II Regions across the Disk of NGC 6946Using the OSIRIS tunable narrowband imager on the 10.4 m GTC (La Palma), we have mapped the SAB(rs)cd galaxy NGC 6946 over a ~7.3 × 7.5 arcmin2 field in the emission lines of the [S II] λλ6717, 6731 doublet, and in Hα. From these maps we have produced catalogs of the Hα luminosities and effective radii of 557 H II regions across the disk, andAlfaro, Emilio J. et al.
Advertised on:
32013 -
Bayesian Analysis of Multiple Harmonic Oscillations in the Solar CoronaThe detection of multiple mode harmonic kink oscillations in coronal loops enables us to obtain information on coronal density stratification and magnetic field expansion using seismology inversion techniques. The inference is based on the measurement of the period ratio between the fundamental mode and the first overtone and theoretical resultsDíaz, A. J. et al.
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32013 -
Temporal Evolution of the Scattering Polarization of the Ca II IR Triplet in Hydrodynamical Models of the Solar ChromosphereVelocity gradients in a stellar atmospheric plasma have an effect on the anisotropy of the radiation field that illuminates each point within the medium, and this may in principle influence the scattering line polarization that results from the induced atomic level polarization. Here, we analyze the emergent linear polarization profiles of the CaCarlin, E. S. et al.
Advertised on:
22013 -
Returning magnetic flux in sunspot penumbraeAims: We study the presence of reversed polarity magnetic flux in sunspot penumbra. Methods: We applied a new regularized method to deconvolve spectropolarimetric data observed with the spectropolarimeter SP onboard Hinode. The new regularization is based on a principal component decomposition of the Stokes profiles. The resulting Stokes profilesAsensio-Ramos, A. et al.
Advertised on:
12013 -
Constraining clumpy dusty torus models using optimized filter setsRecent success in explaining several properties of the dusty torus around the central engine of active galactic nuclei has been gathered with the assumption of clumpiness. The properties of such clumpy dusty tori can be inferred by analysing spectral energy distributions (SEDs), sometimes with scarce sampling given that large aperture telescopesRamos-Almeida, C. et al.
Advertised on:
12013 -
Scattering polarization of hydrogen lines from electric-induced atomic alignmentWe consider a gas of hydrogen atoms illuminated by a broadband unpolarized radiation with zero anisotropy. In the absence of external fields, atomic J-levels are thus isotropically populated. While this condition persists in the presence of a magnetic field, we show instead that electric fields can induce the alignment of these levels. We also showManso Sainz, R. et al.
Advertised on:
42008 -
Evidence for Rotational Motions in the Feet of a Quiescent Solar ProminenceWe present observational evidence of apparent plasma rotational motions in the feet of a solar prominence. Our study is based on spectroscopic observations taken in the He I 1083.0 nm multiplet with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope. We recorded a time sequence of spectra with 34 s cadence placing theOrozco Suárez, D. et al.
Advertised on:
122012 -
Power Spectra of Velocities and Magnetic Fields on the Solar Surface and their Dependence on the Unsigned Magnetic Flux DensityWe have performed power spectral analysis of surface temperatures, velocities, and magnetic fields, using spectropolarimetric data taken with the Hinode Solar Optical Telescope. When we make power spectra in a field of view covering the supergranular scale, kinetic and thermal power spectra have a prominent peak at the granular scale while theKatsukawa, Y. et al.
Advertised on:
102012 -
The Hanle Effect of Lyα in a Magnetohydrodynamic Model of the Solar Transition RegionIn order to understand the heating of the solar corona it is crucial to obtain empirical information on the magnetic field in its lower boundary (the transition region). To this end, we need to measure and model the linear polarization produced by scattering processes in strong UV lines, such as the hydrogen Lyα line. The interpretation of theŠtěpán, J. et al.
Advertised on:
102012 -
LEMUR: Large European module for solar Ultraviolet Research. European contribution to JAXA's Solar-C missionThe solar outer atmosphere is an extremely dynamic environment characterized by the continuous interplay between the plasma and the magnetic field that generates and permeates it. Such interactions play a fundamental role in hugely diverse astrophysical systems, but occur at scales that cannot be studied outside the solar system. Understanding thisTeriaca, Luca et al.
Advertised on:
102012 -
Unusual Stokes V profiles during flaring activity of a delta sunspotAims: We analyze a set of full Stokes profile observations of the flaring active region NOAA 10808. The region was recorded with the Vector-Spectromagnetograph of the Synoptic Optical Long-term Investigations of the Sun facility. The active region produced several successive X-class flares between 19:00 UT and 24:00 UT on September 13, 2005 and weFischer, C. E. et al.
Advertised on:
112012 -
Signal detection for spectroscopy and polarimetryThe analysis of high spectral resolution spectroscopic and spectropolarimetric observations constitutes a very powerful way of inferring the dynamical, thermodynamical, and magnetic properties of distant objects. However, these techniques starve photons, making it difficult to use them for all purposes. A common problem is not being able to detectAsensio-Ramos, A. et al.
Advertised on:
112012 -
Anomalous Circular Polarization Profiles in the He I 1083.0 nm Multiplet from Solar SpiculesWe report Stokes vector observations of solar spicules and a prominence in the He I 1083 nm multiplet carried out with the Tenerife Infrared Polarimeter. The observations show linear polarization profiles that are produced by scattering processes in the presence of a magnetic field. After a careful data reduction, we demonstrate the existence ofMartínez-González, M. J. et al.
Advertised on:
112012 -
Hanle Effect for Stellar Dipoles and QuadrupolesWe derive exact expressions for the degree of lineal polarization over a resolved or integrated stellar disc due to resonance scattering and the Hanle effect from a dipolar or quadrupolar distribution of magnetic fields. We apply the theory of scattering polarization within the formalism of the spherical tensors representation for the densityManso-Sainz, R. et al.
Advertised on:
112012 -
VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic ImagerIn this paper we describe in detail the implementation and main properties of a new inversion code for the polarized radiative transfer equation (VFISV: Very Fast Inversion of the Stokes Vector). VFISV will routinely analyze pipeline data from the Helioseismic and Magnetic Imager (HMI) on-board of the Solar Dynamics Observatory (SDO). It willBorrero, J. M. et al.
Advertised on:
102011 -
The Horizontal Magnetic Flux of the Quiet-Sun Internetwork as Observed with the Hinode Spectro-PolarimeterObservations of very quiet Sun using the Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft reveal that the quiet internetwork regions are pervaded by horizontal magnetic flux. The spatial average horizontal apparent flux density derived from wavelength-integrated measures of Zeeman-induced linear polarization isLites, B. W. et al.
Advertised on:
12008 -
Spectro-polarimetry in the era of large solar telescopesThis paper discusses some of the challenges of spectro-polarimetric observations with a large aperture solar telescope such as the ATST or the EST. The observer needs to reach a compromise between spatial and spectral resolution, time cadence, and signal-to-noise ratio, as only three of those four parameters can be pushed to the limit. TunableSocas-Navarro, H.
Advertised on:
62010 -
Non-local thermodynamic equilibrium inversions from a 3D magnetohydrodynamic chromospheric modelContext. The structure of the solar chromosphere is believed to be governed by magnetic fields, even in quiet-Sun regions that have a relatively weak photospheric field. During the past decade inversion methods have emerged as powerful tools for analyzing the chromosphere of active regions. The applicability of inversions to infer thede la Cruz Rodríguez, J. et al.
Advertised on:
72012 -
Direct Imaging of Fine Structure in the Chromosphere of a Sunspot UmbraHigh-resolution imaging observations from the Hinode spacecraft in the Ca II H line are employed to study the dynamics of the chromosphere above a sunspot. We find that umbral flashes and other brightenings produced by the oscillation are extremely rich in fine structure, even beyond the resolving limit of our observations (0farcs22). The umbra isSocas-Navarro, H. et al.
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52009
