Parameters of sensitivity of Fraunhofer lines to changes in the temperature, gas pressure, and microturbulent velocity in the solar photosphere

TL;DR

This paper introduces parameters to measure how Fraunhofer lines respond to changes in temperature, pressure, and microturbulence in the solar photosphere, aiding physical diagnostics of solar atmospheric conditions.

Contribution

It proposes new sensitivity parameters based on depression response functions calculated in LTE, providing a quantitative tool for solar atmosphere diagnostics.

Findings

Weak lines show greatest relative temperature sensitivity.

Moderate heavy atom lines are most sensitive to temperature.

Strong lines of heavy atoms respond best to microturbulent velocity.

Abstract

Parameters are proposed for measuring the sensitivity of Fraunhofer lines to the physical conditions in the solar atmosphere. The parameters are calculated based on depression response functions in the LTE approximation. The sensitivity of lines to the temperature, gas pressure, and microturbulent velocity depending on the line and atomic parameters is investigated. The greatest relative temperature sensitivity is shown by weak lines, while the greatest absolute sensitivity is displayed by moderate lines of abundant heavy atoms with low ionization and excitation potentials. The excitation potential and line strength are the crucial factors for the temperature sensitivity. The highest pressure sensitivity is observed for moderate lines of light atoms with very high excitation potentials (exceeding 6 eV), and strong photospheric lines (8 pm < W < 14 pm) of heavy atoms are the most responsive to the microturbulent velocity. The sensitivity parameters can be also used to advantage for physical diagnostics of the photosphere when the temperature, pressure, and microturbulent velocity fluctuations are no more than 8%, 50%, and 100%, respectively.