Abstract for Proposal 084031
The impact of Be disks on the X-ray emission of gamma Cas stars
gamma Cas stars are Oe/Be stars that display an intriguing bright and
hard X-ray emission. The origin of this X-ray emission could be either
accretion by a compact companion or an interaction between the Be star and
its decretion disk. Evidence favouring the latter scenario was obtained
over recent years. This includes observations of a quasi-simultaneous
decrease by a factor 10 of the X-ray emission of HD45314 as the disk of
this star nearly dissipated in 2016. We aim at further constraining
the gamma Cas phenomenon by taking advantage of such spectacular
variations. For this purpose, we propose observing a gamma Cas star next
time that its disk undergoes either an outburst or in case it clears away.
Details on Observing Strategy and Trigger Criteria
The goal is to observe a gamma Cas star if its disk suffers an outburst
(H-alpha equivalent width becoming at least 1.5 times more negative than
during quiescence) or nearly disappears (absolute value H-alpha equivalent
width reducing to less than 25% of its quiescence value). The targets
are monitored in optical spectroscopy to provide the trigger criteria. We
will inform the SOC should any of the eight stars that we monitor fulfill
either of the trigger criteria. Given the typical timescales of disk
outbursts or dissipation, a reaction time of about ten days is sufficient.