10.5281/zenodo.4558124
https://zenodo.org/records/4558124
oai:zenodo.org:4558124
Sun, Xudong
Xudong
Sun
0000-0003-4043-616X
University of Hawaii
Török, Tibor
Tibor
Török
0000-0003-3843-3242
Predictive Science Inc
DeRosa, Marc
Marc
DeRosa
0000-0002-6338-0691
Lockheed Martin Solar and Astrophysics Laboratory
Torus-Stable Zone Above Starspots
Zenodo
2021
Cool Stars on the main sequence
The Sun and the Heliosphere
2021-02-23
Poster
10.5281/zenodo.4558123
https://zenodo.org/communities/coolstars20half
Creative Commons Attribution 4.0 International
The torus instability (TI) of current-carrying magnetic flux tubes is thought to drive many solar coronal mass ejections (CMEs). The background magnetic field provides the stabilizing force: if it decreases with height at a rate slower than a critical value, the TI may be suppressed. Here we estimate the vertical extent of a "torus-stable zone" above starspots using a scaled model for the Sun. For a potential-field model comprising a bipole (as a pair of starspots) in alignment with a global dipole, we show that the upper bound of this zone hc increases with the bipole size a, the dipole field with harmonic coefficient g10, and the source surface radius Rs where the magnetic field becomes radial. The value of hc, ranging from about 0.5a to a significant fraction of the stellar radius, depends on the interplay between the spot and dipole magnetic fields; its upper limit is set by Rs. Suppression of the TI may contribute to the lack of CME detection from active cool stars, as larger starspots, stronger dipole, and more closed magnetic topology significantly expand the torus-stable zone.
X. Sun is supported by NSF awards #1848250 and #1854760. T. Török is supported by NSF award ICER-1854790 (PREEVENTS) and by NASA award 80NSSC20K1274.