Magnetic field inference in active region coronal loops using coronal rain clumps

Kriginsky, M., Oliver, R., Antolin, Patrick, Kuridze, D. and Freij, N. (2021) Magnetic field inference in active region coronal loops using coronal rain clumps. Astronomy & Astrophysics, 650. A71. ISSN 0004-6361

2104.03089.pdf - Accepted Version

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Aims. We aim to infer information about the magnetic field in the low solar corona from coronal rain clumps using high-resolution spectropolarimetric observations in the Ca II 8542 Å line obtained with the Swedish 1 m Solar Telescope.

Methods. The weak-field approximation (WFA) provides a simple tool to obtain the line-of-sight component of the magnetic field from spectropolarimetric observations. We adapted a method developed in a previous paper in order to assess the different conditions that must be satisfied in order to properly use the WFA for the data at hand. We also made use of velocity measurements in order to estimate the plane-of-the-sky magnetic field component, so that the magnetic field vector could be inferred.

Results. We have inferred the magnetic field vector from a data set totalling 100 spectral scans in the Ca II 8542 Å line, containing an off-limb view of the lower portion of catastrophically cooled coronal loops in an active region. Our results, albeit limited by the cadence and signal-to-noise ratio of the data, suggest that magnetic field strengths of hundreds of Gauss, even reaching up to 1000 G, are omnipresent at coronal heights below 9 Mm from the visible limb. Our results are also compatible with the presence of larger magnetic field values such as those reported by previous works. However, for large magnetic fields, the Doppler width from coronal rain is not that much larger than the Zeeman width, thwarting the application of the WFA. Furthermore, we have determined the temperature, T, and microturbulent velocity, ξ, of coronal rain clumps and off-limb spicules present in the same data set, and we have found that the former ones have narrower T and ξ distributions, their average temperature is similar, and coronal rain has microturbulent velocities smaller than those of spicules.

Item Type: Article
Additional Information: Funding information: MK and RO acknowledge support from the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER funds through project AYA2017-85465-P. They are also grateful for the travel support received from the International Space Science Institute (Bern, Switzerland) as well as for discussions with members of the ISSI team on “Observed multi-scale variability of coronal loops as a probe of coronal heating”, led by C. Froment and P. Antolin. MK also acknowledges the support from the Vicepresidència i Conselleria d’Innovació, Recerca i Turisme del Govern de les Illes Balears and the Fons Social Europeu 2014-2020 de les Illes Balears. PA acknowledges funding from his STFC Ernest Rutherford Fellowship (No. ST/R004285/2). DK has received funding from the Sêr Cymru II scheme, part-funded by the European Regional Development Fund through the Welsh Government and from the Georgian Shota Rustaveli National Science Foundation project FR17 323. This research has made use of SunPy v1.1, an open-source and free community-developed solar data analysis Python package (The SunPy Community 2020). The Swedish 1 m Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics of Stockholm University in the Spanish Observato-rio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The Institute for Solar Physics is supported by a grant for research infrastructures of national importance from the Swedish Research Council (registration number 2017-00625). The authors would like to thank L. Rouppe van der Voort for his remarkable contribution to this work by performing the reduction of the raw data. Finally, the authors also acknowledge the very useful comments from the anonymous referee that helped to improve the work.
Uncontrolled Keywords: Sun: corona / Sun: magnetic fields
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
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Depositing User: Elena Carlaw
Date Deposited: 12 Aug 2021 10:38
Last Modified: 12 Aug 2021 10:45

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