High‐Resolution Profiles of Diffuse Interstellar Bands

Abstract

High-resolution (R ¼ 115; 000) echelle spectra (acquired with the ESO/ HARPS spectrograph) of a few OB reddened stars, where no Doppler splitting is observed in interstellar atomic lines, are analyzed. The observed profile shapes allow us to divide the diffuse interstellar bands (DIBs) into several sets, characterized by very similar shapes and widths and thus likely carried by similar molecular species. However, not all DIBs behave in the same way; profiles of broader features remain unchanged (are difficult to divide into sets of similar shapes), while evident differences are seen in the narrow ones. Profiles of DIBs may change slightly from object to object, apparently due to different physical parameters in the intervening clouds; this supports the idea of their molecular origin. We also introduce a new parameter, which is a result of dividing the equivalent width of a diffuse band (in m8) by the depth of the feature (in percent). This parameter facilitates grouping of similar DIBs, as well as providing some quantitative information that allows us to estimate the broadness of a feature even for very complex profiles, vastly differing from Gaussian. Subject headingg : ISM: lines and bands