Correlations between diffuse interstellar bands and atomic lines

ABSTRACT We present and discuss correlations between strengths of the well‐known, strong interstellar atomic lines of K i and Ca ii, and four selected, strong unidentified diffuse interstellar bands (DIBs): 5780, 5797, 5850 and 6614. In order to analyse a homogeneous sample of echelle high‐resolution spectra it has been chosen to use measurements from Terskol Observatory in Northern Caucasus plus a selected number of higher resolution observations performed using other instruments. We demonstrate that the strength of certain DIBs correlate well with neutral potassium lines and to a much lower degree with ionized calcium lines. This fact suggests that the degree of irradiation of a cloud with UV photons, capable to ionize interstellar atoms, plays a crucial role in the formation/maintenance of certain molecular species: possible carriers of DIBs.