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   81251
   ASCA have detected X-rays from two intermediate-mass pre-main-sequence
   stars (Herbig Ae/Be stars: HAEBEs) in the early phase of 1E5-years-old.
   TheX-rays showed thin-thermal emission of 3-5keV with rapid flares and
   resemble ones of low-mass protostars. Therefore, we suspect that all
   stars in this age show magnetic activities, which decay in the older
   stage. To verify this hypothesis, we observe four young HAEBEs with
   different stellar masses. The objectives are to search X-ray flares and
   to derive plasma temperature in a quiescent state. By comparing it with
   the X-ray properties of older HAEBEs, we could find the decaying time
   scale of magnetic activities and the relation to the stellar wind
   activities. This study will reveal the evolution of high-energy
   phenomena of young stars.
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