Physical conditions in CaFe interstellar clouds

TL;DR

This paper models the physical conditions of CaFe interstellar clouds, revealing their solar-like composition, high electron densities, and lack of element depletion onto dust grains.

Contribution

It introduces a model for ionisation equilibrium in CaFe clouds, showing their unique physical and chemical properties compared to typical interstellar clouds.

Findings

CaFe clouds have high electron densities (~1 cm^-3).

They exhibit solar-like chemical composition with no element depletion.

Ionisation equilibrium modeling explains observed column densities.

Abstract

Interstellar clouds that exhibit strong Ca I and Fe I lines were called CaFe clouds. The ionisation equilibrium equations were used to model the column densities of Ca II, Ca I, K I, Na I, Fe I and Ti II in CaFe clouds. The chemical composition of CaFe clouds is that of the Solar System and no depletion of elements onto dust grains is seen. The CaFe clouds have high electron densities n=1 cm^-3 that leads to high column densities of neutral Ca and Fe.