C$_{60}^+$ diffuse interstellar band correlations and environmental variations

Abstract

The Diffuse Interstellar Bands (DIBs) are absorption features seen in the spectra of astronomical objects, that arise in the interstellar medium. Today more than 500 DIBs have been observed mostly in the optical and near-infrared wavelengths. The origin of the DIBs are unclear; only ionized buckminsterfullerene C$_{60}^+$ has been identified as a viable candidate for two strong and three weaker DIBs. In this study, we investigate the correlations between the strengths of the two strongest C$_{60}^+$ DIBs as well as their environmental behaviour. Therefore, we analysed measurements of the strengths of the two C$_{60}^+$ DIBs at 9577 and 9633 $\r{A}$ for 26 lines of sight. We used two different methods, including Monte Carlo simulations, to study their correlations and the influence of measurement errors on the correlation coefficients. Furthermore, we examined how the strength of the C$_{60}^+$ DIBs changes as a result of different environmental conditions, as measured by the concentration of H/H$_2$ and the strength of the ambient UV radiation. In contrast to results recently reported by Galazutdinov et al. (2021), we find a high correlation between the strengths of the C$_{60}^+$ DIBs. We also discovered that the behaviour of the correlated C$_{60}^+$ bands is quite distinct from other DIBs at 5780, 5797 and 6203 $\r{A}$ in different environments.