A study of the dynamical evolution of delta Scorpii

Abstract

Context: Be stars are main-sequence, early type stars whose spectrum is characterized by the presence of emission lines of HI, He and other metals. This emission comes from a circumstellar disk, whose origin is attributed to material that is ejected by the fast-spinning central star. Aims: the Be star delta Scorpii was diskless (i.e., a normal B star) during all of the XX century, but in 2000 it started developing a disk that survives until today. Our group has a very rich observational dataset of this star that covers most of the disk evolution with a variety of different techniques (photometry, polarimetry, interferometry and spectroscopy). The objective of this work is to model the recent history of theBe star delta Scorpii in the context of recent advancements of the theory of the circumstellar disks around Be stars. Methods: Be disks are believed to form from material ejected from the central star that diffuses outwards by means of viscous forces, in a process known as viscous decretion. Therefore, the "viscosity parameter" is fundamental in controlling the history and fate of these disks. As a result, the construction and dissipation of Be circumstellar disks offer the possibility of measuring this parameter with great accuracy. This has been done, for the first time, in a recent study of the dissipation of the disk around the star 28 CMa. We will apply the same method to fit dynamical disk models to the observables of the Be star delta Scorpii. Expected results: delta Sco offers the unique opportunity to model the entire disk evolution since its formation in 2000 to the present day activity. Contrary to what has been done for 28 CMa, for which the viscosity parameter was obtained by analyzing only the disk dissipation phase, the here proposed analysis will model all phases of disk evolution. This will constitute a quite stringent test of the viscous decretion disk model. In addition, with this work, we aim at addressing the scientific questions of whether or not the viscosity parameter varies with disk density and distance from the star. (AU)