Issue |
A&A
Volume 656, December 2021
Solar Orbiter First Results (Cruise Phase)
|
|
---|---|---|
Article Number | L4 | |
Number of page(s) | 11 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202140380 | |
Published online | 14 December 2021 |
Letter to the Editor
Extreme-UV quiet Sun brightenings observed by the Solar Orbiter/EUI
1
Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium
e-mail: david.berghmans@oma.be
2
Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
3
UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
4
Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
5
Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
6
ETH-Zürich, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
7
Adnet Systems Inc., NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771, USA
8
Institute of Applied Computing & Community Code, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
9
Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992 Moscow, Russia
10
Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK
11
Centre Spatial de Liège, Université de Liège, Av. du Pré-Aily B29, 4031 Angleur, Belgium
12
European Space Agency (ESA/ESTEC), Keplerlaan 1, PO Box 299 2200 AG Noordwijk, The Netherlands
13
Institute of Geodynamics of the Romanian Academy, Bucharest, Romania
Received:
19
January
2021
Accepted:
1
April
2021
Context. The heating of the solar corona by small heating events requires an increasing number of such events at progressively smaller scales, with the bulk of the heating occurring at scales that are currently unresolved.
Aims. The goal of this work is to study the smallest brightening events observed in the extreme-UV quiet Sun.
Methods. We used commissioning data taken by the Extreme Ultraviolet Imager (EUI) on board the recently launched Solar Orbiter mission. On 30 May 2020, the EUI was situated at 0.556 AU from the Sun. Its High Resolution EUV telescope (HRIEUV, 17.4 nm passband) reached an exceptionally high two-pixel spatial resolution of 400 km. The size and duration of small-scale structures was determined by the HRIEUV data, while their height was estimated from triangulation with simultaneous images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory mission. This is the first stereoscopy of small-scale brightenings at high resolution.
Results. We observed small localised brightenings, also known as ‘campfires’, in a quiet Sun region with length scales between 400 km and 4000 km and durations between 10 s and 200 s. The smallest and weakest of these HRIEUV brightenings have not been previously observed. Simultaneous observations from the EUI High-resolution Lyman-α telescope (HRILya) do not show localised brightening events, but the locations of the HRIEUV events clearly correspond to the chromospheric network. Comparisons with simultaneous AIA images shows that most events can also be identified in the 17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although they appear weaker and blurred. Our differential emission measure analysis indicated coronal temperatures peaking at log T ≈ 6.1 − 6.15. We determined the height for a few of these campfires to be between 1000 and 5000 km above the photosphere.
Conclusions. We find that ‘campfires’ are mostly coronal in nature and rooted in the magnetic flux concentrations of the chromospheric network. We interpret these events as a new extension to the flare-microflare-nanoflare family. Given their low height, the EUI ‘campfires’ could stand as a new element of the fine structure of the transition region-low corona, that is, as apexes of small-scale loops that undergo internal heating all the way up to coronal temperatures.
Key words: Sun: UV radiation / Sun: transition region / Sun: corona / instrumentation: high angular resolution
© ESO 2021
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