HD 87643 : a B E star with a cold wind.

Abstract

Ultraviolet observations of the B/e/ star HD 87643 have revealed the presence of a wind in low ionization species with outflow velocities of up to 800 km/s in the Mg II doublet. The dominating species in the spectrum are the once-ionized metals, mostly Fe II. The P Cyg profiles of the Mg II lines have a structure similar to that of the Balmer lines. The behavior of the Fe II lines is complex, with profiles ranging from an almost pure emission to an almost pure absorption. P Cyg profiles are represented in the first UV multiplets. The observed properties of the Fe II lines can be explained in terms of a resonance fluorescence mechanism plus optical depth effects in an expanding medium. The mass-loss rate derived after a detailed evaluation of the ionization equilibrium throughout the envelope is about 10 to the -7th solar mass per year. A semiqualitative model for the outer layers, consisting of four different regions, is proposed.