The 5780-diffuse Band In Peculiar Interstellar Clouds

This paper presents the spectra of a sample of galactic stars in which the broad diffuse interstellar band at 5780 angstrom is strongly attenuated in relation to their colour excess and the neighbour feature at 5797 angstrom is absent. The unusually large width of the 5780 band which is found in the direction of the Orion Trapezium stars is discussed in terms of intrinsic and Doppler broadening. The same clouds (apparently fragments of the Orion parent cloud) are known to produce peculiar extinction. It is suggested that the high density of collapsing clouds facilitates sticking of the diffuse band carriers to grain surfaces where they loose their identity reacting with the bulk of grain material. The process of sticking also alters the optical properties of grains.