Origin of the Blue Continuum Radiation in the Flare Spectra of dMe stars

TL;DR

This paper investigates the origin of the blue continuum radiation in dMe star flares, showing it originates from near-photospheric layers, and concludes that shock wave models cannot fully explain the observed blackbody radiation at flare peaks.

Contribution

It provides a detailed calculation of hydrogen plasma emission spectra considering nonlinear effects, clarifying the source of blue continuum in stellar flares.

Findings

Blue continuum arises from near-photospheric layers during flares.

Shock wave models do not produce the observed blackbody radiation.

Nonlinear effects significantly influence emission spectra calculations.

Abstract

Calculations of the emission spectrum of a homogeneous plane layer of pure hydrogen plasma taking into account nonlinear effects (the influence of bremsstrahlung and recombination radiation of the layer itself on its Menzel factors) [Morchenko et al., Ap&SS, Vol. 357, article id. 119 (2015)] show that the blue component of the optical continuum during the impulsive phase of large flares on dMe stars originates from the near-photospheric layers [Grinin and Sobolev, Afz, Vol. 13, 587 (1977)]. The gas behind the front of a stationary radiative shock wave propagating in the red dwarf chromosphere toward the photosphere is not capable of generating the blackbody radiation observed at the maximum brightness of the flares.