Affiliation: | (1) Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica, Casilla 306, Santiago 22, Chile;(2) Department of Physics, University of Warwick, Coventry, CV4 7AL, UK;(3) Departamento de Física, Universidad de Concepción, Casilla 306-C, Concepción, Chile;(4) European Southern Observatory, Casilla, 19001, Santiago 19, Chile |