Issue |
A&A
Volume 687, July 2024
|
|
---|---|---|
Article Number | A138 | |
Number of page(s) | 10 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202449541 | |
Published online | 04 July 2024 |
The corona of a fully convective star with a near-polar flare
1
Leibniz Institute for Astrophysics Potsdam (AIP),
An der Sternwarte 16,
14482
Potsdam,
Germany
2
ASTRON, Netherlands Institute for Radio Astronomy,
Oude Hoogeveensedijk 4,
Dwingeloo,
7991
PD,
The Netherlands
e-mail: ilin@astron.nl
3
Institute for Physics and Astronomy, University of Potsdam,
Karl-Liebknecht-Strasse 24/25,
14476
Potsdam,
Germany
4
Institut für Astronomie & Astrophysik, Eberhard Karls Universität Tübingen,
Sand 1,
72076
Tübingen,
Germany
Received:
8
February
2024
Accepted:
6
May
2024
Context. In 2020, the Transiting Exoplanet Survey Satellite (TESS) observed a rapidly rotating M7 dwarf, TIC 277539431, producing a flare at 81° latitude, the highest latitude flare located to date. This is in stark contrast to solar flares that occur much closer to the equator, typically below 30°. The mechanisms that allow flares at high latitudes to occur are poorly understood.
Aims. We studied five sectors of TESS monitoring, and obtained 36 ks of XMM-Newton observations to investigate the coronal and flaring activity of TIC 277539431.
Methods. From the observations, we infer the optical flare frequency distribution; flare loop sizes and magnetic field strengths; the soft X-ray flux, luminosity, and coronal temperatures; as well as the energy, loop size, and field strength of a large flare in the XMM-Newton observations.
Results. We find that the corona of TIC 277539431 does not differ significantly from other low-mass stars on the canonical saturated activity branch with respect to coronal temperatures and flaring activity, but shows lower luminosity in soft X-ray emission by about an order of magnitude, consistent with other late M dwarfs.
Conclusions. The lack of X-ray flux, the high-latitude flare, the star’s viewing geometry, and the otherwise typical stellar corona taken together can be explained by the migration of flux emergence to the poles in rapid rotators like TIC 277539431 that drain the star’s equatorial regions of magnetic flux, but preserve its ability to produce powerful flares.
Key words: stars: coronae / stars: flare / stars: rotation
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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