General
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
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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A Novel Investigation of the Small-scale Magnetic Activity of the Quiet Sun via the Hanle Effect in the Sr I 4607 Å Line
One of the key research problems in stellar physics is to decipher the small-scale magnetic activity of the quiet solar atmosphere. Recent magneto-convection simulations that account for small-scale dynamo action have provided three-dimensional (3D) models of the solar photosphere characterized by a high degree of small-scale magnetic activity
del Pino Alemán, T. et al.Advertised on:
82018 -
Enhancing SDO/HMI images using deep learning
Context. The Helioseismic and Magnetic Imager (HMI) provides continuum images and magnetograms with a cadence better than one per minute. It has been continuously observing the Sun 24 h a day for the past 7 yr. The trade-off between full disk observations and spatial resolution means that HMI is not adequate for analyzing the smallest-scale events
Díaz Baso, C. J. et al.Advertised on:
62018 -
Inversions of synthetic umbral flashes: Effects of scanning time on the inferred atmospheres
Context. The use of instruments that record narrowband images at selected wavelengths is a common approach in solar observations. They allow scanning of a spectral line by sampling the Stokes profiles with two-dimensional images at each line position, but require a compromise between spectral resolution and temporal cadence. The interpretation and
Felipe, T. et al.Advertised on:
62018 -
High-resolution imaging and near-infrared spectroscopy of penumbral decay
Aims: Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us to scrutinize the velocity and magnetic fields of sunspots and their surroundings. Methods: Active region NOAA 12597 was observed on 2016 September 24 with the 1.5-meter GREGOR solar telescope using high-spatial
Verma, M. et al.Advertised on:
62018 -
Small-scale Magnetic Flux Emergence in the Quiet Sun
Small bipolar magnetic features are observed to appear in the interior of individual granules in the quiet Sun, signaling the emergence of tiny magnetic loops from the solar interior. We study the origin of those features as part of the magnetoconvection process in the top layers of the convection zone. Two quiet-Sun magnetoconvection models
Moreno-Insertis, F. et al.Advertised on:
62018 -
The Magnetic Response of the Solar Atmosphere to Umbral Flashes
Chromospheric observations of sunspot umbrae offer an exceptional view of magnetoacoustic shock phenomena and the impact they have on the surrounding magnetically dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine fluctuations
Houston, S. J. et al.Advertised on:
62018 -
Alfvén wave dissipation in the solar chromosphere
Magnetohydrodynamic Alfvén waves1 have been a focus of laboratory plasma physics2 and astrophysics3 for over half a century. Their unique nature makes them ideal energy transporters, and while the solar atmosphere provides preferential conditions for their existence4, direct detection has proved difficult as a result of their evolving and dynamic
Grant, Samuel D. T. et al.Advertised on:
52018 -
On the Importance of the Nonequilibrium Ionization of Si IV and O IV and the Line of Sight in Solar Surges
Surges are ubiquitous cool ejections in the solar atmosphere that often appear associated with transient phenomena like UV bursts or coronal jets. Recent observations from the Interface Region Imaging Spectrograph show that surges, although traditionally related to chromospheric lines, can exhibit enhanced emission in Si IV with brighter spectral
Nóbrega-Siverio, D. et al.Advertised on:
52018 -
The magnetic nature of umbra-penumbra boundary in sunspots
Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of
Jurčák, J. et al.Advertised on:
32018 -
Possible Photometric Signatures of Moderately Advanced Civilizations: The Clarke Exobelt
This paper puts forward a possible new indicator of the presence of moderately advanced civilizations on transiting exoplanets. The idea is to examine the region of space around a planet where potential geostationary or geosynchronous satellites would orbit (hereafter, the Clarke exobelt). Civilizations with a high density of devices and/or space
Socas-Navarro, H.Advertised on:
32018 -
High-resolution Observations of Hα Spectra with a Subtractive Double Pass
High-resolution imaging spectroscopy in solar physics has relied on Fabry-Pérot interferometers (FPIs) in recent years. FPI systems, however, become technically challenging and expensive for telescopes larger than the 1 m class. A conventional slit spectrograph with a diffraction-limited performance over a large field of view (FOV) can be built at
Beck, C. et al.Advertised on:
22018 -
Magneto-optical Effects in the Scattering Polarization Wings of the Ca I 4227 Å Resonance Line
The linear polarization pattern produced by scattering processes in the Ca I 4227 Å resonance line is a valuable observable for probing the solar atmosphere. Via the Hanle effect, the very significant Q/I and U/I line-center signals are sensitive to the presence of magnetic fields in the lower chromosphere with strengths between 5 and 125 G
Alsina Ballester, E. et al.Advertised on:
22018 -
Center-to-limb variation of the continuum intensity and linear polarization of stars with transiting exoplanets
Not Available
Shchukina, N. G. et al.Advertised on:
72017 -
The First Post-Kepler Brightness Dips of KIC 8462852
We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in 2015 October, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth
Boyajian, T. S. et al.Advertised on:
12018 -
Structure of sunspot light bridges in the chromosphere and transition region
Context. Light bridges (LBs) are elongated structures with enhanced intensity embedded in sunspot umbra and pores. Aims: We studied the properties of a sample of 60 LBs observed with the Interface Region Imaging Spectrograph (IRIS). Methods: Using IRIS near- and far-ultraviolet spectra, we measured the line intensity, width, and Doppler shift
Rezaei, R.Advertised on:
12018 -
Ca II 8542 Å brightenings induced by a solar microflare
Aims: We study small-scale brightenings in Ca II 8542 Å line-core images to determine their nature and effect on localized heating and mass transfer in active regions. Methods: High-resolution two-dimensional spectroscopic observations of a solar active region in the near-infrared Ca II 8542 Å line were acquired with the GREGOR Fabry-Pérot
Kuckein, C. et al.Advertised on:
122017 -
Signatures of the impact of flare-ejected plasma on the photosphere of a sunspot light bridge
Aims: We investigate the properties of a sunspot light bridge, focusing on the changes produced by the impact of a plasma blob ejected from a C-class flare. Methods: We observed a sunspot in active region NOAA 12544 using spectropolarimetric raster maps of the four Fe I lines around 15 655 Å with the GREGOR Infrared Spectrograph, narrow-band
Felipe, T. et al.Advertised on:
122017 -
The Temperature - Magnetic Field Relation in Observed and Simulated Sunspots
Observations of the relation between continuum intensity and magnetic field strength in sunspots have been made for nearly five decades. This work presents full-Stokes measurements of the full-split (g = 3) line Fe i 1564.85 nm with a spatial resolution of 0.5^'' obtained with the GREGOR Infrared Spectrograph in three large sunspots. The continuum
Sobotka, M. et al.Advertised on:
122017 -
Comparison of Solar Fine Structure Observed Simultaneously in Lyα and Mg ii h
The Chromospheric Lyman Alpha Spectropolarimeter (CLASP) observed the Sun in H i Lyα during a suborbital rocket flight on 2015 September 3. The Interface Region Imaging Telescope (IRIS) coordinated with the CLASP observations and recorded nearly simultaneous and co-spatial observations in the Mg ii h and k lines. The Mg ii h and Lyα lines are
Schmit, D. et al.Advertised on:
102017 -
A Si I atomic model for NLTE spectropolarimetric diagnostics of the 10 827 Å line
Aims: The Si i 10 827 Å line is commonly used for spectropolarimetric diagnostics of the solar atmosphere. First, we aim at quantifying the sensitivity of the Stokes profiles of this line to non-local thermodynamic equilibrium (NLTE) effects. Second, we aim at facilitating NLTE diagnostics of the Si i 10 827 Å line. To this end, we propose the use
Shchukina, N. G. et al.Advertised on:
72017
