Flare Induced Photospheric Velocity Diagnostics

TL;DR

This study uses radiative hydrodynamic simulations to analyze how electron beam heating during solar flares affects photospheric Fe I line profiles, revealing complex chromospheric contributions that can mislead velocity diagnostics.

Contribution

It demonstrates the importance of considering chromospheric emission effects when interpreting photospheric line profiles during solar flares.

Findings

Chromospheric emission can produce apparent redshifts in line profiles.

Line synthesis shows significant chromospheric contribution to photospheric lines.

Velocity signals during flares can be misinterpreted due to chromospheric effects.

Abstract

We present radiative hydrodynamic simulations of solar flares generated by the RADYN and RH codes to study the perturbations induced in photospheric Fe I lines by electron beam heating. We investigate how variations in the beam parameters result in discernible differences in the induced photospheric velocities. Line synthesis revealed a significant chromospheric contribution to the line profiles resulting in an apparent red asymmetry by as much as 40 m/s close to the time of maximum beam heating which was not reflective of the upflow velocities that arose from the radiative hydrodynamic simulations at those times. The apparent redshift to the overall line profile was produced by significant chromospheric emission that was blueshifted by as much as 400 m/s and fills in the blue side of the near stationary photospheric absorption profile. The velocity information that can be retrieved from photospheric line profiles during flares must therefore be treated with care to mitigate the effects of higher parts of the atmosphere providing an erroneous velocity signal.