The relation between 5780 and 5797 diffuse interstellar bands, CH/CH⁺ molecules, and atomic or molecular hydrogen

Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, 85-072 Bydgoszcz, Poland
e-mail: towes@gazeta.pl

Received: 5 November 2018
Accepted: 16 March 2019

Abstract

Correlations between column densities of neutral and molecular hydrogen and strengths of major 5780 and 5797 Å diffuse interstellar bands (DIBs) based on spectra of 66 OB stars were analyzed. We confirm that the 5797 Å DIB is more tightly correlated with column density of molecular hydrogen while the 5780 DIB – with that of atomic hydrogen. This leads to a reasonably tight relation between the molecular fraction of H₂ and equivalent width ratio of the 5797 and 5780 major diffuse bands with correlation coefficient equal to 0.77 ± 0.05. Column densities of CH and CH⁺ molecules were used to analyze correlations between abundances of CH/CH⁺ molecules and strengths of the major 5780 and 5797 DIBs. The 5780 DIB is better correlated with the column density of methydyline cation than the 5797 DIB. A relation with correlation coefficient equal to 0.95 ± 0.02 based on precise column densities, between column densities of CH and H₂ molecules, is also presented; in other words, the column densitiy ratio in the case of H₂ and CH molecules in the ISM is equal to (2.01 ± 0.09) × 10⁷.