Magnetic structure in cool stars. XVI. Emissions from the outer atmospheres of M-type dwarfs.
Mewe, R.; Rutten, R. G. M.; Schrijver, C. J.; Duncan, D. K.; Zwaan, C.
Netherlands, United States
Abstract
Consideration is given to emission from the outer atmospheres of M-type dwarfs in several spectral lines originating from the chromosphere, the transition-region, and the soft X-ray emission from the corona. It is shown that M-type dwarfs systematically deviate from relations between flux densities in soft X-rays and chromospheric and transition-region emission lines. The quantitative relation between the equivalent width of H-alpha and the Ca II, H, and K emission index is determined. It is suggested that the emission in the Balmer spectrum may result from back heating by coronal soft X-rays.