The Be Binary Delta Scorpii and Its 2011 Periastron Passage

Delta Scorpii is an unusal Be binary system. The binarity was discovered by interferometry in the 1970's and only confirmed 
by radial velocity measurements during the periastron passage in September 2000, when the primary component became a 
Be star. The components brightness and mass suggest that both are normal B-type stars. However, the large orbital 
eccentricity (e=0.94) is highly uncommon, as most such Be binaries have circular orbits. The orbital period, only recently 
constrained by interferometry at 10.81 years, needed confirmation from spectroscopy during the last periastron passage in 
July 2011. The periastron observing campaign that involved professionals and amateurs resulted in obtaining several hundreds 
of spectra during the period of a large radial velocity change compared to only thirty obtained in 2000. Along with a 
determination of the orbital period accurate to 3-4 days, the radial velocity curve was found to be more complicated than one 
expected from just a binary system. I will start with a brief review of the primary's disk development followed by a discussion 
of the recent observations. Implications for the system properties and ideas for future observations will be presented.