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

    • Helioseismic holography of simulated sunspots: dependence of the travel time on magnetic field strength and Wilson depression

      Improving methods for determining the subsurface structure of sunspots from their seismic signature requires a better understanding of the interaction of waves with magnetic field concentrations. We aim to quantify the impact of changes in the internal structure of sunspots on local helioseismic signals. We have numerically simulated the

      Felipe, T. et al.

      Advertised on:

      8
      2017
      Citations
      8
    • Zeeman effect in sulfur monoxide. A tool to probe magnetic fields in star forming regions

      Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral

      Cazzoli, G. et al.

      Advertised on:

      9
      2017
      Citations
      8
    • Comparison of Damping Mechanisms for Transverse Waves in Solar Coronal Loops

      We present a method to assess the plausibility of alternative mechanisms to explain the damping of magnetohydrodynamic transverse waves in solar coronal loops. The considered mechanisms are resonant absorption of kink waves in the Alfvén continuum, phase mixing of Alfvén waves, and wave leakage. Our methods make use of Bayesian inference and model

      Montes-Solís, M. et al.

      Advertised on:

      9
      2017
      Citations
      12
    • Chromospheric polarimetry through multiline observations of the 850-nm spectral region - II. A magnetic flux tube scenario

      In this publication, we continue the work started in Quintero Noda et al., examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the physical phenomena that take place in it, in particular, the magnetic pumping, leaves a specific imprint on the examined spectral lines. We find that the profiles

      Suematsu, Y. et al.

      Advertised on:

      11
      2017
      Citations
      14
    • Solar polarimetry through the K I lines at 770 nm

      We characterize the K I D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca II infrared triplet lines and several Zeeman sensitive photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in

      Suematsu, Y. et al.

      Advertised on:

      9
      2017
      Citations
      13
    • Discovery of Scattering Polarization in the Hydrogen Lyα Line of the Solar Disk Radiation

      There 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 polarimetric

      Kano, R. et al.

      Advertised on:

      4
      2017
      Citations
      46
    • Penumbral thermal structure below the visible surface

      Context. 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 stratification

      Borrero, J. M. et al.

      Advertised on:

      5
      2017
      Citations
      8
    • Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm Lines

      The 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 scattering

      Ishikawa, R. et al.

      Advertised on:

      5
      2017
      Citations
      16
    • The dusty tori of nearby QSOs as constrained by high-resolution mid-IR observations

      We 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 arcsec

      Martínez-Paredes, M. et al.

      Advertised on:

      6
      2017
      Citations
      25
    • Uncertainties in the solar photospheric oxygen abundance

      Aims: 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 atlases

      Cubas Armas, M. et al.

      Advertised on:

      3
      2017
      Citations
      5
    • Spectropolarimetric Evidence for a Siphon Flow along an Emerging Magnetic Flux Tube

      We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the sunrise balloon-borne solar observatory. We obtain the full vector magnetic field and the line of sight (LOS) velocity through inversions of the Fe i line

      Requerey, I. S. et al.

      Advertised on:

      3
      2017
      Citations
      5
    • Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration

      The 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-minutes

      Giono, G. et al.

      Advertised on:

      4
      2017
      Citations
      11
    • Inference of the chromospheric magnetic field orientation in the Ca ii 8542 Å line fibrils

      Context. 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 association

      Asensio Ramos, A. et al.

      Advertised on:

      3
      2017
      Citations
      32
    • Dependence of sunspot photospheric waves on the depth of the source of solar p-modes

      Photospheric waves in sunspots moving radially outward at speeds faster than the characteristic wave velocities have been recently detected. It has been suggested that they are the visual pattern of p-modes excited around 5 Mm beneath the sunspot's surface. Using numerical simulations, we performed a parametric study of the waves observed at the

      Felipe, T. et al.

      Advertised on:

      2
      2017
      Citations
      9
    • Observations of Ellerman bomb emission features in He i D3 and He i 10 830 Å

      Context. Ellerman bombs (EBs) are short-lived emission features, characterised by extended wing emission in hydrogen Balmer lines. Until now, no distinct signature of EBs has been found in the He i 10 830 Å line, and conclusive observations of EBs in He i D3 have never been reported. Aims: We aim to study the signature of EBs in neutral helium

      Libbrecht, T. et al.

      Advertised on:

      1
      2017
      Citations
      29
    • Synthetic polarimetric spectra from stellar prominences

      Stellar 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 model

      Felipe, T. et al.

      Advertised on:

      2
      2017
      Citations
      1
    • How to infer the Sun's global magnetic field using the Hanle effect

      We present a different approach to determine the characteristics of the global magnetic field of the Sun based on the study of the Hanle signals. The Hanle effect of a stellar dipole produces a surface asymmetric pattern of linear polarization that depends on the strength and geometry of this global field. Moreover, if the dipole is misaligned with

      Vieu, T. et al.

      Advertised on:

      3
      2017
      Citations
      1
    • Gyro-viscosity and linear dispersion relations in pair-ion magnetized plasmas

      A fluid theory has been developed by taking account of gyro-viscosity to study wave propagation characteristics in a homogeneous pair-ion magnetized plasma with a cylindrical symmetry. The exact dispersion relations derived by the Hankel-Fourier transformation are shown comparable with those observed in the experiment by Oohara and co-workers. The

      Kono, M. et al.

      Advertised on:

      11
      2015
      Citations
      0
    • Oscillations and Waves in Sunspots

      A magnetic field modifies the properties of waves in a complex way. Significant advances have been made recently in our understanding of the physics of sunspot waves with the help of high-resolution observations, analytical theories, as well as numerical simulations. We review the current ideas in the field, providing the most coherent picture of

      Khomenko, E. et al.

      Advertised on:

      11
      2015
      Citations
      77
    • Evershed flow observed in neutral and singly ionized iron lines

      The amplitudes of the Evershed flow are measured using pairs of carefully selected Fe i and Fe ii spectral lines that are close in wavelength and registered simultaneously. A sunspot belonging to the NOAA 11582 group was scanned using the spectrograph of the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). Velocities were extracted

      Khomenko, E. et al.

      Advertised on:

      12
      2015
      Citations
      10

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