Establishing new diffuse interstellar band correlations to identify common carriers

Observations from the Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands (DIBs) were analysed to establish highly correlated pairs in terms of their equivalent widths (EWs) (r > 0.95), which importantly facilitate the identification of common carriers. A total of 154 846 possible DIB pairs were originally examined, yet only those with a sufficient number of sightlines (n > 9) that included EW uncertainties were subsequently investigated. The highest correlations for the resulting 56 893 DIB pairs are 6284.05–6203.58 Å (r = 0.990 ± 0.001), 6203.58–5780.64 Å (r = 0.986 ± 0.001), 6993.12–6269.89 Å (r = 0.984 ± 0.001), 6843.76–6792.51 Å (r = 0.984 ± 0.005), 6203.58–5487.64 Å (r = 0.983 ± 0.002), and 5061.50–4969.12 Å (r = 0.983 ± 0.009). The bands 5363.77, 5780.64, 6203.58, and 6284.05 Å appear most frequently. Novel relations linked to those DIBs and others warrant further research, in particular those pairs that involve one or both DIBs with low EWs (e.g. 5609.82, 6269.89, 6993.12, and 7224.16 Å). Numerous DIBs correlated with the prominent 4429.33 Å band were also discovered. The intriguing proposal of anionic hydrogen clusters as possible DIB carriers is also discussed.