Classical Be星為演化至主序末期且自轉快速(300km/s)的星球，它們的觀測特徵為光譜中的發射線以及超過光球的紅外輻射。其紅外超量源於離子氣體的自由態間發射。然而，少數J-H及H-K皆大於0.6星等者，則是Classical Be星沿赤道表面的氣體拋出後，凝華為塵埃。這些塵埃吸收星光後，產生明顯的紅外超量。本文計算電漿的自由態間發射，貢獻在紅外超量所達到的極限。並且針對六顆具有高度紅外超量Be星球探討其演化的狀態。

Classical Be stars are B-type main sequence stars with one or more Balmer lines in emission, characterized by their rotational velocity (up to 300 km s−1), and circumstellar gas distributed in shell-, disk- or ring like configuration. Classical Be stars also are associated with infrared excess attibuted to free-free emission from ionized gas. A few with exceptionally large infrared excess, namely with J-H, and H-K both greater than 0.6 mag, however, must be accounted for by thermal emission from circumstellar dust which is condensed out in the flattened, expanding envelope as these fast-rotating stars evolve to the giant phase. This thesis calculates the extent plasma free-free emission can contribute to the near-infrared excess observed in the JHK color-color diagram and in the spectral energy distribution seen in the classical Be stars. We made detailed studies of 6 Be stars that show large JHK excess, and clarify their status of being classical Be stars, as opposed to Herbig Ae/Be stars, which are intermediate-mass pre-main sequence stars, whose infrared excess arise from surplus star forming circumstellar dust.

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