Solar and Stellar Magnetism

    General
    Description

    Magnetic fields are at the base of star formation and stellar structure and evolution. When stars are born, magnetic fields brake the rotation during the collapse of the mollecular cloud. In the end of the life of a star, magnetic fields can play a key role in the form of the strong winds that lead to the last stages of stellar evolution. During the whole adult life of a star, magnetic fields are the origin of stellar activity. Our Sun has magnetic fields that give rise to such spectacular activity that impacts the climate on Earth. The magnetic activity in other stars is, in some cases, of orders of magnitude more intense than the solar one, influencing – often drastically – the transport of chemical species and angular momentum, as well as affecting the possible planetary systems around them.

    The aim of this project is the study of the diverse manifestations of the magnetic field that can be observed in the solar atmosphere and in other stars. These include distinct structures as sunspots, weak quiet-sun fields or chromospheric and coronal features such as filaments and prominences. The following research topics have been gradually faced:

    Solar magnetism

    1. Structure and evolution of Sunspot magnetic fields.

    2. Structure and evolution of quiet Sun magnetic fields.

    3. Structure and evolution of the magnetism of the chromosphere and of chromospheric strcutures (promiences, spicules,...)

    4. Structure and evolution or coronal loops.

    5. Structure and evolution of the Sun's global field. Studies of the activity cycle.

    6. Empirical study of propagation of magnetohydrodynamic waves in magnetic structures.

    7. Empirical study of energy transfer mechanisms related with the heating of the external atmospheric layers.

    8. Empirical study of the influence of partial ionisation in the dynamics of the solar atmosphere.

    9. Participation in the European Solar Telescope project.

    Stellar magnetism

    1. Development of numerical tools to diagnose stellar magnetic fields, both in the surface and in the chromsphere.

    2. Study of magnetic fields in stellar prominences.

    3. Study of the role of magnetic fields in the late stages of stellar evolution.

    Principal investigator
    Project staff
    1. Spiral waves in sunspots: They have been interpreted as magnetoacoustic waves propagating from the interior to the atmosphere following the direction of the magnetic field. We have characterized the magnetic field topology, dismissing the twist of the field lines as the cause of the spiral shape (Felipe et al. 2019).
    2. Magnetic response to umbral flashes: Simultaneous spectropolarimetric observations of the chromospheric He I 10830 and Ca II 8542 lines have been used to estimate the fluctuations of the magnetic field associated to shock waves. The shocks cause expansion of the magnetic field lines (Houston et al. 2018, including A. Asensio Ramos).

    Related publications

    • An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities
      This paper describes an adaptation of the Optimally Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere, assuming that the atmosphere and radiation field are
      Agrawal, Piyush et al.

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      2
      2023
      Citations
      0
    • Exploring Magnetic Loops and Serpentine Fields in the Quiet Sun with the GRIS-IFU
      Synthetic observations produced from radiative magnetohydrodynamic simulations have predicted that higher polarization fractions in the quiet solar photosphere would be revealed by increasing the total integration time of observations at GREGOR resolutions. We present recently acquired disk center observations of the Fe I 15648.5 Å line obtained
      Collados, Manuel et al.

      Advertised on:

      2
      2023
      Citations
      1
    • The role of cooling induced by mixing in the mass and energy cycles of the solar atmosphere
      In many astrophysical systems, mixing between cool and hot temperature gas/plasma through Kelvin-Helmholtz-instability-driven turbulence leads to the formation of an intermediate temperature phase with increased radiative losses that drive efficient cooling. The solar atmosphere is a potential site for this process to occur with interaction between
      Hillier, Andrew et al.

      Advertised on:

      4
      2023
      Citations
      6
    • Impact of opacity effects on chromospheric oscillations inferred from NLTE inversions
      Context. Spectropolarimetric inversions are a fundamental tool for diagnosing the solar atmosphere. Chromospheric inferences rely on the interpretation of spectral lines that are formed under nonlocal thermodynamic equilibrium (NLTE) conditions. In the presence of oscillations, changes in the opacity impact the response height of the spectral lines
      Felipe, T. et al.

      Advertised on:

      2
      2023
      Citations
      5
    • Solar-cycle and Latitude Variations in the Internetwork Magnetism
      The importance of the quiet-Sun magnetism is that it is always there to a greater or lesser extent, being a constant provider of energy, independently of the solar cycle phase. The open questions about the quiet-Sun magnetism include those related to its origin. Most people claim that the local dynamo action is the mechanism that causes it. This
      Trelles Arjona, J. C. et al.

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      2
      2023
      Citations
      1
    • Magnetic field amplification and structure formation by the Rayleigh-Taylor instability
      We report our results from a set of high-resolution, two-fluid, non-linear simulations of the magnetized Rayleigh Taylor instability (RTI) at the interface between a solar prominence and the corona. These data follow results reported earlier on linear and early non-linear RTI dynamics in this environment. This paper is focused on the generation and
      Popescu Braileanu, B. et al.

      Advertised on:

      2
      2023
      Citations
      10
    • Vortex Motions in the Solar Atmosphere
      Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the
      Tziotziou, K. et al.

      Advertised on:

      2
      2023
      Citations
      13
    • Towards the Identification and Classification of Solar Granulation Structures Using Semantic Segmentation
      Solar granulation is the visible signature of convective cells at the solar surface. The granulation cellular pattern observed in the continuum intensity images is characterised by diverse structures e.g., bright individual granules of hot rising gas or dark intergranular lanes. Recently, the access to new instrumentation capabilities has given us
      Díaz Castillo, S. M. et al.

      Advertised on:

      6
      2022
      Citations
      1
    • Optical design of an image-slicer integral field unit with two output slits
      The optical design of an integral field unit (IFU) based on image-slicers represents an interesting design exercise because of the small size of the components and the critical parameters to reduce optical aberrations. When the IFU to be designed is also intended to substitute an IFU prototype that is already integrated into a spectropolarimeter
      Vaz Cedillo, Jacinto J. et al.

      Advertised on:

      1
      2022
      Citations
      0
    • Polarimetric characterization of segmented mirrors
      We study the impact of the loss of axial symmetry around the optical axis on the polarimetric properties of a telescope with segmented primary mirror when each segment is present in a different aging stage. The different oxidation stage of each segment as they are substituted in time leads to non-negligible crosstalk terms. This effect is
      Collados, M. et al.

      Advertised on:

      6
      2022
      Citations
      1
    • Large Ion-neutral Drift Velocities and Plasma Heating in Partially Ionized Coronal Rain Blobs
      In this paper we present a numerical study of the dynamics of partially ionized coronal rain blobs. We use a two-fluid model to perform a high-resolution 2D simulation that takes into account the collisional interaction between the charged and neutral particles contained in the plasma. We follow the evolution of a cold plasma condensation as it
      Martínez-Gómez, David et al.

      Advertised on:

      12
      2022
      Citations
      7
    • FarNet-II: An improved solar far-side active region detection method
      Context. Activity on the far side of the Sun is routinely studied through the analysis of the seismic oscillations detected on the near side using helioseismic techniques such as phase-shift sensitive holography. Detections made through those methods are limited to strong active regions due to the need for a high signal-to-noise ratio. Recently
      Broock, E. G. et al.

      Advertised on:

      11
      2022
      Citations
      1
    • Observational and numerical characterization of a recurrent arc-shaped front propagating along a coronal fan
      Context. Recurrent, arc-shaped intensity disturbances were detected by extreme-ultraviolet channels in an active region. The fronts were observed to propagate along a coronal loop bundle rooted in a small area within a sunspot umbra. Previous works have linked these intensity disturbances to slow magnetoacoustic waves that propagate from the lower
      Sieyra, M. V. et al.

      Advertised on:

      11
      2022
      Citations
      2
    • Ambipolar Diffusion in the Lower Solar Atmosphere: Magnetohydrodynamic Simulations of a Sunspot
      Magnetohydrodynamic (MHD) simulations of the solar atmosphere are often performed under the assumption that the plasma is fully ionized. However, in the lower solar atmosphere a reduced temperature often results in only the partial ionization of the plasma. The interaction between the decoupled neutral and ionized components of such a partially
      MacBride, Conor D. et al.

      Advertised on:

      10
      2022
      Citations
      4
    • Polarization Accuracy Verification of the Chromospheric LAyer SpectroPolarimeter
      We have developed an advanced UV spectropolarimeter called Chromospheric LAyer SpectroPolarimeter (CLASP2), aimed at achieving very high accuracy measurements (<0.1% at 3 σ ) of the linear (Q /I and U /I ) and circular (V /I ) polarizations of the Mg II h and k lines (280 nm). CLASP2 was launched on board a NASA sounding rocket on April 11, 2019
      Song, Donguk et al.

      Advertised on:

      10
      2022
      Citations
      3
    • Evidence of a flare ignited above a low-latitude spotted active region in the ultrafast rotator HK Aqr
      We study the magnetic activity in the ultrafast rotator dMe HK Aqr using tomography techniques with high-resolution spectroscopy. We aim to characterize how this magnetic activity appears in a regime of very fast rotation without external forces, given that HK Aqr is, very likely, a single star. We find dark spots located at low latitudes. We also
      Martínez González, María Jesús et al.

      Advertised on:

      11
      2022
      Citations
      1
    • The European Solar Telescope
      The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes
      Quintero Noda, C. et al.

      Advertised on:

      10
      2022
      Citations
      35
    • Quiet Sun Center to Limb Variation of the Linear Polarization Observed by CLASP2 Across the Mg II h and k Lines
      The CLASP2 (Chromospheric LAyer Spectro-Polarimeter 2) sounding rocket mission was launched on 2019 April 11. CLASP2 measured the four Stokes parameters of the Mg II h and k spectral region around 2800 Å along a 200″ slit at three locations on the solar disk, achieving the first spatially and spectrally resolved observations of the solar
      Rachmeler, L. A. et al.

      Advertised on:

      9
      2022
      Citations
      17
    • First Light of the Integral Field Unit of GRIS on the GREGOR Solar Telescope
      An Integral Field Unit (IFU) based on image slicers has been added to the GREGOR Infrared Spectrograph (GRIS). This upgrade to the instrument makes possible 2D spectropolarimetry in the near-infrared by simultaneously recording the full Stokes profiles of spectral lines (in a given spectral interval) at all the points in the field of view (FOV). It
      Dominguez-Tagle, C. et al.

      Advertised on:

      7
      2022
      Citations
      5
    • Doppler-velocity Drifts Detected in a Solar Prominence
      We analyzed multiline observations of a quiescent prominence from the slit spectrograph located at the Ondřejov Observatory. Dopplergrams and integrated intensity maps of the whole prominence were obtained from observations in six spectral lines: Ca II H, Hϵ, Hβ, He I D3, Hα, and Ca II IR. By combining integrated intensity maps with non-LTE
      Zapiór, Maciej et al.

      Advertised on:

      7
      2022
      Citations
      11

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