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   81252
   Hard tail variability in early-type stars have been believed to have no
   magnetic field, and the X-rays come from the stellar wind. Recently,
   some objections to this standard understanding have beenreported;
   detection of X-ray hard tails with power law shape; evidence of the
   plasma ejection from the stellar surface; a large scale optical depth
   variation originated on the stellar surface.  From these observational
   context, we suppose that the X-ray hard tail comes from a magnetically
   confined hot plasma on the stellar surface, hence the X-ray hard tail
   must bevariable.  In order to examine this possibility, we propose a
   long term observation of a bright B0 star, tau Sco.
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