The graphite rich Cepheus OB3 association.

Abstract

The four optically brightest stars of the Cepheus OB 3 association have been observed with the IUE satellite in the spectral range 1150-3200 A. The extinction suffered by the stars has been investigated. Both the shape of the bump at approximately 2200 A and the behavior of the extinction at longer wavelengths are close to those of the mean interstellar curve. The behavior shortward of 2000 A is peculiar and reveals the existence of a component of dust which belongs to the association. A fit with theoretical extinction curves shows that a strong excess of graphite relative to silicates in the local component is required to explain the observed extinction in the Cepheus OB 3 association.