Glossary term: 亞矮星
Description: 亞矮星是一類比主序列中相同光譜型恆星更暗，但比相同溫度的白矮星更亮的恆星。
亞矮星通常分為兩類：冷亞矮星和熱亞矮星。
大多數亞矮星都屬於冷亞矮星，在赫羅圖上比主序低一到兩個星等，這是因為它們含有的比氦（天文學中稱為金屬）重的元素非常少。這改變了光和熱在它們內部和大氣中的傳播方式，使它們變得更小、更熱、更暗。
在太陽系附近的銀河系區域，亞矮星屬於銀河暈或銀河盤的較老部分，形成於銀河系的早期階段。這是因為每一代恆星都會通過核聚變產生更多的金屬，並將其中的一部分返回星際介質--恆星形成的氣體庫。因此，年輕恆星比老恆星擁有更多的金屬。因此，金屬含量較少的亞矮星通常是較老的恆星。
還有少量光譜型為 O 和 B 的熱亞矮星（稱為 sdO 星和 sdB 星）。天文學家並不清楚這些天體是如何形成的，但一個可能的原因是巨星由於某種原因失去了外層。外層脫落的原因尚不確定，但其中一個可能的原因是巨星的外層被雙星伴星吸積而剝離。
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
This is an automated transliteration of the simplified Chinese translation of this term
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