Quiescent and flaring lyman-α radiation of host stars and effects on exoplanets

Lyman-α radiation dominates the ultraviolet spectra of G, K, and M stars and is a major photodissociation source for H2O, CO2, and CH4 in the upper atmospheres of exoplanets. We obtain intrinsic Lyman-α line fluxes for late-type stars by correcting for interstellar absorption or by scaling from other spectroscopic observables. When stars flare, all emission lines brighten by large factors as shown by HST spectra. We describe photochemical models of the atmosphere of the mini-Neptune GJ 436b (Miguel et al. 2015) that show the effects of flaring Lyman-α fluxes on atmospheric chemical abundances.

Massive stars: flare activity due to infalls of comet-like bodies

Passages of comet-like bodies through the atmosphere/chromosphere of massive stars at velocities more than 600 km/s will be accompanied, due to aerodynamic effects as crushing and flattening, by impulse generation of hot plasma within a relatively very thin layer near the stellar surface/photosphere as well as “blast” shock wave, i.e., impact-generated photospheric stellar/solar flares. Observational manifestations of such high-temperature phenomena will be eruption of the explosive layer's hot plasma, on materials of the star and “exploding” comet nuclei, into the circumstellar environment and variable anomalies in chemical abundances of metal atoms/ions like Fe, Si etc. Interferometric and spectroscopic observations/monitoring of young massive stars with dense protoplanetary discs are of interest for massive stars physics/evolution, including identification of mechanisms for massive stars variability.