Oscillations in the line-of-sight magnetic field strength in a pore observed by the GREGOR Infrared Spectrograph (GRIS)

C. J. Nelson*, R. J. Campbell, M. Mathioudakis

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Context. Numerous magnetohydrodynamic oscillations have been reported within solar pores over the past few decades, including in line-of-sight (LOS) velocities, intensities, and magnetic field strengths. Aims. Our aim is to identify whether high-amplitude oscillations in the LOS magnetic field strength can be detected within a pore located in Active Region 12748 and to investigate which physical mechanisms could be responsible for them. Methods. A solar pore was observed on 1 September 2019 using the GREGOR Infrared Spectrograph instrument for around one hour. Full-Stokes vectors were sampled in a 37 Å window containing the Fe I 15 648.52 Å line (effective Landé g factor of 3). The LOS magnetic field strength was inferred using the strong-field approximation. Additionally, the Stokes Inversion based on Response functions code was used to gain a more complete understanding of the physical properties of the solar atmosphere at the locations of these oscillations. Results. Oscillations of more than 100 G are observed in the LOS magnetic field in the period window between 600 and 1272 s at three localised (> 1″2) regions. These oscillations have coherence across individual regions, indicating that jitter cannot account for their occurrence. Longer-period amplitude variations, amplitudes over 200 G, are also detected, but they have periods outside of the cone-of-influence. Numerical inversions confirm both oscillations in the LOS magnetic field strength at optical depths of around log τ5000 =-0.5 (potentially caused by compression) and other effects (e.g. changes in the optical depth or the inclination of the magnetic field) may account for these changes. Conclusions. The oscillations in the separations of the Stokes-V lobes of the 15 648.52 Å line appear to be solar in nature. Future work will be required to understand whether these are truly oscillations in the magnetic field strength at a specific depth in the solar atmosphere or whether other effects are responsible for these signatures.

Original languageEnglish
Article numberA50
JournalAstronomy and Astrophysics
Volume654
DOIs
Publication statusPublished - 08 Oct 2021

Bibliographical note

Funding Information:
Acknowledgements. The authors are indebted to C. Dominguez-Tagle, J. Rendtel, and M. Collados for their help with data collection and reduction. C.J.N. and M.M. are thankful to the Science and Technology Facilities Council (STFC) for the support received to conduct this research through grant numbers ST/P000304/1 & ST/T00021X/1. This research data leading to the results obtained has been supported by SOLARNET project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no 824135. R.J.C. acknowledges support from the Northern Ireland Department for the Economy (DfE) for the award of a PhD studentship. Wavelet software was provided by C. Torrence and G. Compo, and is available at URL: http://atoc.colorado.edu/research/wavelets/. The 1.5-m GREGOR solar telescope was built by a German consortium under the leadership of the Leibniz-Institute for Solar Physics (KIS) in Freiburg with the Leibniz Institute for Astrophysics Potsdam, the Institute for Astrophysics Göttingen, and the Max Planck Institute for Solar System Research in Göttingen as partners, and with contributions by the Instituto de Astrofísica de Canarias and the Astronomical Institute of the Academy of Sciences of the Czech Republic. The redesign of the GREGOR AO and instrument distribution optics was carried out by KIS whose technical staff is gratefully acknowledged. SDO/HMI data are courtesy of NASA/SDO and the HMI science team.

Publisher Copyright:
© 2021 ESO.

Keywords

  • Sun: atmosphere
  • Sun: magnetic fields
  • Sun: oscillations
  • Sun: photosphere

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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