The CO Fundamental Band as an LTE Diagnostic of the Temperature Minimum

Abstract:

Spectral and spectro-polarimetric inversion techniques are a powerful set of tools capable of inferring the 3-D structure of the solar atmosphere from a set of observed atomic spectral lines. However, the degree to which an inversion can retrieve the true solar atmospheric profiles depends on the formation properties of the observed lines, as well as the complexity of the physics involved in the inversion. In this work, we invert DST/IBIS observations of several atomic lines (Na I 589.6 nm, Fe I 709.0 nm, and Ca II 854.2 nm, which together sample the lower photosphere to the mid chromosphere) using the Stockholm Inversion Code (STiC) for the temperature and velocity structure in the vicinity of a decaying sunspot observed on 02/14/2011. The results of these inversions are compared to simultaneous observations of the fundamental (Δν=1) ro-vibrational band of CO, which is comprised of dozens of individual molecular lines with varying strengths and formation properties. These lines form in LTE and can be used to sample the properties of the Solar temperature minimum; therefore, by comparing the inversion results to maps of CO column density and brightness temperature, we can determine the fidelity of the NLTE STiC inversions in inferring the qualities of the temperature minimum. Particular focus is given to several CO-rich “cold spots” which appear in the vicinity of the sunspot remnant during the observing sequence.