Abstract for Proposal 096375

X-raying the transition in pi Aqr

With its bright and hard X-ray emission, pi Aqr belongs to the growing category of gamma Cas objects amongst Be stars. Its decretion disk is currently undergoing a transition. A preparatory XMM observation already revealed changes at the start of the event. Now we request a new observation, to be taken when the transition is further developed. Such data will shed a crucial light on the origin of the mysterious X-ray emission of gamma Cas objects.

Details on Observing Strategy and Trigger Criteria
The observation would be triggered in one of the visibility windows if the disk has sufficiently dissipated (polarization degree < 0.2%). The target is monitored in the optical. As Be stars evolve slowly, reaction time does not need to be short (a week or more is perfectly ok and even needed to schedule the simultaneous optical observations).