Fast inversion of solar Ca II spectra

TL;DR

This paper introduces a rapid inversion method for solar Ca II spectra using a precomputed spectral archive under LTE assumptions, with a non-LTE correction derived for improved accuracy.

Contribution

The authors develop a fast inversion code that significantly reduces computation time and provides a first-order non-LTE correction for LTE-derived temperature stratifications.

Findings

Inversion time per profile is less than 1 second.

Non-LTE correction factors range from near 1 to 4 depending on atmospheric depth.

Method is applicable to various spectrograph data types.

Abstract

We present a fast (<< 1 s per profile) inversion code for solar Ca II lines. The code uses an archive of spectra that are synthesized prior to the inversion under the assumption of local thermodynamic equilibrium (LTE). We show that it can be successfully applied to spectrograph data or more sparsely sampled spectra from two-dimensional spectrometers. From a comparison to a non-LTE inversion of the same set of spectra, we derive a first-order non-LTE correction to the temperature stratifications derived in the LTE approach. The correction factor is close to unity up to log tau ~ -3 and increases to values of 2.5 and 4 at log tau = -6 in the quiet Sun and the umbra, respectively.