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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DeepVel: Deep learning for the estimation of horizontal velocities at the solar surfaceMany 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 basedAsensio Ramos, A. et al.
Advertised on:
72017 -
Search for torsional oscillations in isolated sunspotsIn this work we seek evidence for global torsional oscillations in alpha sunspots. We have used long time series of continuum intensity and magnetic field vector maps from the Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO) spacecraft. The time series analysed here span the total disk passage of 25Griñón-Marín, A. B. et al.
Advertised on:
72017 -
Numerical simulations of quiet Sun magnetic fields seeded by the Biermann batteryThe 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 solarKhomenko, E. et al.
Advertised on:
82017 -
A Hot Downflowing Model Atmosphere for Umbral Flashes and the Physical Properties of Their Dark FibrilsWe perform non-LTE inversions in a large set of umbral flashes, including the dark fibrils visible within them, and in the quiescent umbra by using the inversion code NICOLE on a set of full Stokes high-resolution Ca ii λ8542 observations of a sunspot at disk center. We find that the dark structures have Stokes profiles that are distinct from thoseHenriques, V. M. J. et al.
Advertised on:
82017 -
CLASP/SJ Observations of Rapid Time Variations in the Lyα Emission in a Solar Active RegionThe Chromospheric Lyα SpectroPolarimeter (CLASP) is a sounding rocket experiment launched on 2015 September 3 to investigate the solar chromosphere and transition region. The slit-jaw (SJ) optical system captured Lyα images with a high time cadence of 0.6 s. From the CLASP/SJ observations, many variations in the solar chromosphere and transitionIshikawa, Sh.-N. et al.
Advertised on:
92017 -
The Physics and Diagnostic Potential of Ultraviolet SpectropolarimetryThe empirical investigation of the magnetic field in the outer solar atmosphere is a very important challenge in astrophysics. To this end, we need to identify, measure and interpret observable quantities sensitive to the magnetism of the upper chromosphere, transition region and corona. This paper provides an overview of the physics and diagnosticTrujillo Bueno, J. et al.
Advertised on:
92017 -
Design of an adaptable Stokes polarimeter for exploring chromospheric magnetismThe chromosphere is a highly complex and dynamic layer of the Sun, that serves as a conduit for mass and energy supply between two, very distinct regions of the solar atmosphere, namely, the photosphere and corona. Inferring magnetic fields in the chromosphere, has thus become an important topic, that can be addressed with large-aperture solarLouis, R. E. et al.
Advertised on:
102017 -
Chromospheric impact of an exploding solar granuleContext. Observations of multi-wavelength and therefore height-dependent information following events throughout the solar atmosphere and unambiguously assigning a relation between these rapidly evolving layers are rare and difficult to obtain. Yet, they are crucial for our understanding of the physical processes that couple the different regimesRezaei, R. et al.
Advertised on:
62017 -
Discovery of Scattering Polarization in the Hydrogen Lyα Line of the Solar Disk RadiationThere is a thin transition region (TR) in the solar atmosphere where the temperature rises from 10,000 K in the chromosphere to millions of degrees in the corona. Little is known about the mechanisms that dominate this enigmatic region other than the magnetic field plays a key role. The magnetism of the TR can only be detected by polarimetricKano, R. et al.
Advertised on:
42017 -
Penumbral thermal structure below the visible surfaceContext. The thermal structure of the penumbra below its visible surface (i.e., τ5 ≥ 1) has important implications for our present understanding of sunspots and their penumbrae: their brightness and energy transport, mode conversion of magneto-acoustic waves, sunspot seismology, and so forth. Aims: We aim at determining the thermal stratificationBorrero, J. M. et al.
Advertised on:
52017 -
Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm LinesThe Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provided the first successful measurement of the linear polarization produced by scattering processes in the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In this paper, we report that the Si iii line at 120.65 nm also shows scatteringIshikawa, R. et al.
Advertised on:
52017 -
The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk CenterBefore using three-dimensional (3D) magnetohydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundanceBeck, C. et al.
Advertised on:
62017 -
The dusty tori of nearby QSOs as constrained by high-resolution mid-IR observationsWe present mid-infrared (MIR; 7.5-13.5 μm) imaging and spectroscopy observations obtained with the CanariCam (CC) instrument on the 10.4-m Gran Telescopio CANARIAS for a sample of 20 nearby, MIR bright and X-ray luminous quasi-stellar objects (QSOs). We find that for the majority of QSOs the MIR emission is unresolved at angular scales ∼0.3 arcsecMartínez-Paredes, M. et al.
Advertised on:
62017 -
Uncertainties in the solar photospheric oxygen abundanceAims: The purpose of this work is to better understand the confidence limits of the photospheric solar oxygen abundance derived from three-dimensional models using the forbidden [OI] line at 6300 Å, including correlations with other parameters involved. Methods: We worked with a three-dimensional empirical model and two solar intensity atlasesCubas Armas, M. et al.
Advertised on:
32017 -
The Physical Origin and Magnetic Sensitivity of the Scattering Polarization Observed in the O i IR Triplet at 777 nmThe linearly polarized solar limb spectrum caused by the absorption and scattering of anisotropic radiation has a very rich diagnostic potential, given its sensitivity to the thermal, dynamic, and magnetic structure of the solar atmosphere. A crucial first step toward its scientific exploitation is understanding the physical origin of the observeddel Pino Alemán, T. et al.
Advertised on:
42017 -
Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight CalibrationThe Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding rocket instrument designed to measure for the first time the linear polarization of the hydrogen Lyman-{α} line (121.6 nm). The instrument was successfully launched on 3 September 2015 and observations were conducted at the solar disc center and close to the limb during the five-minutesGiono, G. et al.
Advertised on:
42017 -
The Transfer of Resonance Line Polarization with Partial Frequency Redistribution in the General Hanle–Zeeman RegimeThe spectral line polarization encodes a wealth of information about the thermal and magnetic properties of the solar atmosphere. Modeling the Stokes profiles of strong resonance lines is, however, a complex problem both from a theoretical and computational point of view, especially when partial frequency redistribution (PRD) effects need to beAlsina Ballester, E. et al.
Advertised on:
22017 -
Inference of the chromospheric magnetic field orientation in the Ca ii 8542 Å line fibrilsContext. Solar chromospheric fibrils, as observed in the core of strong chromospheric spectral lines, extend from photospheric field concentrations suggesting that they trace magnetic field lines. These images have been historically used as proxies of magnetic fields for many purposes. Aims: Use statistical analysis to test whether the associationAsensio Ramos, A. et al.
Advertised on:
32017 -
First Detection of Sign-reversed Linear Polarization from the Forbidden [O I] 630.03 nm LineWe report on the detection of linear polarization of the forbidden [O i] 630.03 nm spectral line. The observations were carried out in the broader context of the determination of the solar oxygen abundance, an important problem in astrophysics that still remains unresolved. We obtained spectro-polarimetric data of the forbidden [O i] line at 630.03de Wijn, A. G. et al.
Advertised on:
22017 -
Synthetic polarimetric spectra from stellar prominencesStellar prominences detected in rapidly rotating stars serve as probes of the magnetism in the corona of cool stars. We have synthesized the temporal evolution of the Stokes profiles generated in the He I 10 830 and 5876 Å triplets during the rotation of a prominence around a star. The synthesis was performed with the HAZEL code using a cloud modelFelipe, T. et al.
Advertised on:
22017
