Spectroscopic observations of the delta Scorpii binary during its recent periastron passage

The bright star delta Sco has been considered a typical B0-type object for many years. Spectra of the star published prior to 1990 showed no evidence of emission, but only of short-term line profile variations attributed to n onradial pulsations. Speckle interferometric observations show that delta S co is a binary system with a highly-eccentric orbit and a period of similar to 10.6 years. Weak emission in the H alpha line was detected in its spect rum for the first time during a periastron passage in 1990. Shortly before the next periastron passage in the summer of 2000, the binary entered a str ong H alpha emission and enhanced mass-loss phase. We monitored the spectro scopic development of the Be outburst from July 2000 through March 2001. In this paper we present results from our spectroscopy, refine elements of th e binary orbit, and discuss possible mechanisms for the mass loss.