Invisibility of Solar Active Region Umbra-to-Umbra Coronal Loops: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal Heating
Abstract
How magnetic energy is injected and released in the solar corona, keeping it heated to several million degrees, remains elusive. The corona is shaped by the magnetic field that fills it and the heating of the corona generally increases with increasing strength of the field. For each of two bipolar solar active regions having one or more sunspots in each of the two main opposite-polarity domains of magnetic flux, from comparison of a nonlinear force-free model of the active region's three-dimensional coronal magnetic field to observed extreme-ultraviolet coronal loops, we find that (1) umbra-to-umbra loops, despite being rooted in the strongest magnetic flux at both ends, are invisible, and (2) the brightest loops have one foot in a sunspot umbra or penumbra and the other foot in another sunspot's penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidence that magnetoconvetion drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Broadly, our results indicate that depending on the field strength in both feet, the photospheric feet of a coronal loop on any convective star can either engender or quench coronal heating in the body of the loop.
This work was supported by funding from the Heliophysics Division of NASA's Science Mission Directorate, from NASA's Postdoctoral Program, and from the Austrian Science Fund. The results have been published in The Astrophysical Journal Letters (Tiwari, S. K., Thalmann, J. K., Panesar, N. K., Moore, R. L., & Winebarger, A. R. 2017, ApJ Letters, 843:L20).- Publication:
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American Astronomical Society Meeting Abstracts #234
- Pub Date:
- June 2019
- Bibcode:
- 2019AAS...23410603M