仙王座β型變星

仙王座β型變星，也稱為大犬座β型變星。這種變星的變光快速但幅度很小，亮度變化被認為是由於鐵在內部20萬K下的異常性質，造成表面的脈動。這些變星通常是光譜為B型的藍白色高溫恆星。不要與造父變星混淆，後者以造父一（仙王座δ）為原型命名，是亮超巨星。 仙王座β型變星是質量介於7至20 M ⊙ {\displaystyle _{\odot }} （太陽質量）的主序星。這些成員中有一些是天空中最亮的恆星，例如十字架三和馬腹一；角宿一也被歸類為仙王座β型變星，但在1970年神秘的停止了脈動。通常，它們的亮度變化在0.01至0.3星等，週期0.1至0.3日（2.4至7.2小時）。做為原型的上衛增一（仙王座β）視星等在 +3.16 到 +3.27 間變化，週期為4.57小時。亮度最亮的時刻發生在恆星最小且最熱的時刻。它們在紫外線上的亮度變化要大得多，可以達到1個星等。少數恆星的變光週期被發現短於一小時，對應於基礎的徑向脈動週期的四分之一和基礎週期的八分之三。它們也有相對較低的振幅和相當窄的光譜類型B2-3 IV-V。它們被稱為短週期組，在GCVS的縮寫是BCEPS。 仙王座β型變星的脈動式是由卡伯機制和p-模式脈動驅動。在恆星內部，溫度高達20萬K的深處，有豐富的鐵。鐵在如此的高溫下，不透明度將增加（不是減少），導致能量在數層之內累積。這會導致壓力的增加而反覆地向外推出與落回，一個循環的週期約數小時。這被稱為鐵凹凸或Z凹凸（Z習慣上是表示金屬量）。這與慢脈動B星（英语：Slowly pulsating B star）類似，顯示同樣是由鐵的不透明度變化驅動的p-模式脈動，但是有著較低的質量和較長的週期。 美國天文學家Edwin Brant Frost（英语：Edwin Brant Frost）在1902年發現仙王座β徑向速度的變化，最初的結論說是聯星的光譜。Paul Guthnick（英语：Paul Guthnick）在1913年率先檢測到它的亮度變化。不久之後，發現軍市一（大犬座β）和心宿一（天蝎座σ）也是變星， 維斯托·斯里弗在1940年指出，心宿一的徑向速度也有變化，還有R.D. Levee和奧托·斯特魯維分別在1952年和1955年推論出這是由於恆星的脈動。 這種變星因為大犬座β星是20世紀末對其研究最密切的例子，因此通常稱為大犬座β型變星，然而它在南部低空的位置，意味著它的觀測經常會受到阻礙。然而，因為仙王座β是第一顆被發現的這種類型變星，所以儘管有和造父變星相似而被混淆的風險，這一類型還是被稱為仙王座β型變星。 塞西莉亞·佩恩-加波施金和Sergei Gaposchkin（英语：Sergei Gaposchkin）在他們1938顆變星的目錄中收錄了17顆可能是這類型的變星，但是將它們歸類為矮造父變星（盾牌座δ型變星）。車府增十五（蝎虎座16）是在1952年之前被廣泛研究的另一這類型的變星。在1966年，此類型變星的數量從18顆增加為41顆。 奧托·斯特魯維在20世紀50年代廣泛的研究這種變星，然而在他逝世之後，研究就減少了。 Christiaan L. Sterken和Mikolaj Jerzykiewicz 在1993年將59顆恆星歸類為仙王座β型變星，並將79顆列為疑似仙王座β型變星。 Stankov在2005年列出93顆成員，77顆候選者，還有61顆可能不是或確定不是這類型的變星。6顆，分別是天棓五（武仙座ι）、雙魚座53、九州殊口四（波江座ν）、壁宿一（飛馬座γ）、英仙座V354（英语：HD 13745）和白羊座53被並列為仙王座β型變星和SPB。 Samus N.N., Durlevich O.V., et al. Combined General Catalog of Variable Stars（GCVS4.2, 2004 Ed.） BSJ. The Beta Cephei Stars and Their Relatives. Variable Star of the Season. American Association of Variable Star Observers. 16 July 2010 [2 August 2015]. （原始内容存档于2020-11-05）.  Lesh, Janet Roundtree; Aizenman, Morris L. The Observational Status of the β Cephei Stars. 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