Are Some Stellar Coronae Optically Thick?

Are stellar coronae optically thin in X-rays? A systematic investigation of opacity effects

The relevance of resonant scattering in the solar corona has always been discussed controversially. Ratios of emission lines from identical ions but different oscillator strengths have been used in order to estimate damping of resonance lines due to possible resonant scattering, i.e., absorption by photo-excitation and re-emission out of the line of sight. The analysis of stellar spectra in ana...

Physics of Stellar Coronae

Solar and Stellar Coronae

The existence of hot coronae throughout the HR diagram has been proved by the observations of the Einstein observatory since the late 1970's This nding has stimulated a new interest in the study of stellar activity. The general picture relating stellar activity in late type stars to the internal generation, photospheric emergence, and chromospheric and coronal dissipation of magnetic elds, was ...

Multiwavelength Aspects of Stellar Coronae

Coronae express different facets of their energy release processes in different wavelength regions. While soft X-ray and EUV emission dominates the radiative losses of the thermal plasma, hard X-ray emission (>10 keV) can be produced from non-thermal high-energy particles accelerated as a consequence of flare processes, and radio emission is often emitted from mildly relativistic electrons trap...

Flare Heating in Stellar Coronae

An open question in the field of solar and stellar astrophysics is the source of heating that causes stellar coronae to reach temperatures of millions of degrees. One possibility is that the coronae are heated by a large number of small flares. On the Sun, flares with energies as low as those of microflares are distributed with energy as a power law of the form dN dE ∝ E −α with α ≈ 1.8, and α ...