E-type asteroids: Spectroscopic investigation on the 0.5 mu m absorption band

Visible spectra of five E-type asteroids have been obtained at the European Southern Observatory with the 1.5-m telescope. Three of these objects reve al a peculiar absorption band centered around 0.5 mum whose origin is not e asily attributable, A possible source might be troilite, which is also a known constituent of a ubrite meteorites, as it has a spectral behavior consistent with the visibl e and near infrared spectrum of these objects and may be responsible not on ly for the 0.5-mum band but probably also for the 3-mum band observed on th e surface of these objects. We report in this paper the results of our inve stigation and a discussion regarding the possible composition of E-type ast eroids. (C) 2001 Academic Press.