On the Unexpectedly Strong X-Ray Luminosity of Coronal Emission in Mid-M-type Dwarfs: Is Resonant Behavior Involved?

The mechanical energy flux F mech created by convective motions in the Sun is predominantly deposited into the chromosphere . The relatively weak coronal heating in the Sun seems to depend on whatever residual F mech is “left over” once the chromosphere has absorbed most of F mech . Data suggest that solar-like behavior (i.e., weakness of coronal heating relative to chromospheric heating) persists in stars over the broad spectral range F-G-K. However, a pronounced change in behavior occurs among M dwarfs: coronal emission becomes unexpectedly strong in comparison to chromospheric emission. In M dwarfs, the partitioning of F mech between chromosphere and corona appears different from solar partitioning. Certain theories have been proposed to account for this weak-to-strong transition in coronal heating (compared to chromospheric). Here, I suggest that a resonant process may be operating in M dwarfs: one such process was proposed by J. A. Ionson in his electrodynamic theory of coronal heating.