Broadened profiles of diffuse interstellar bands

Abstract

ABSTRACT The paper describes profile broadening and peak wavelength variation of diffuse interstellar bands (DIBs) measured for 46 lines of sight, probably caused by the physical properties of intervening clouds. The full width at half-maximum of four studied DIBs (5780, 5797, 6196 and 6614 Å) demonstrates strong variability, sometimes doubling the widths of the features. Despite the high magnitude of the effect, our current analysis is restricted to the strongest DIBs because the weaker ones require a much higher signal-to-noise ratio. The profile broadening in the studied DIBs moves the profile’s centres towards longer wavelengths, probably due to the excitation of higher levels of the P branch of the unknown molecular carrier. Moreover, DIBs are broader in clouds with abundantly populated vibrationally excited states of hydrogen molecules; that is, the broadening of DIBs correlates with the rotational temperature estimated on the H2ν= 2 vibrational level. However, objects that demonstrate extremely broadened profiles of DIBs are scarce. The extreme peculiarity of the DIB profiles was detected in Herschel 36. Here we show the gradual growths of the widths of DIBs, confirmed in spectra from different instruments.