天鵝座α型變星

天鵝座α型變星是顯示出非徑向脈動的變星，意味著當恆星表面有些地方收縮時，而同時也有些地方是擴張的^[1]。它們是光譜類型B或A的超巨星，亮度變化在0.1視星等，並與脈動相關聯，而由於和多脈動週期的節拍相關聯，因而通常是不規則變星。脈衝週期通常有幾天到幾個星期的周期。

這種變星的原型是天津四（天鵝座α），顯示的亮度在1.21 和 +1.29 之間波動。眾所周知很多在早期的超巨星都有小幅快速的變動，但之前它們未被歸為一類，直到1985年的變星總表第四版才收錄為變星的一種，縮寫的字母為ACYG（Alpha Cygni variable stars）^[2]。許多高光度藍變星（LBVs）在它們平靜（熱）階段顯示出天鵝座α型變星的型態，但在這種情況下一般仍使用LBV的分類。

克裡斯托費爾（Christoffel Waelkens）和他的同事在1998年的研究，分析依巴谷衛星的資料，發現了大量（32）此類變星^[3]。

脈動

還不完全清楚天鵝座α型變星的脈動，它們並不限於窄幅的溫度和光度脈動星的方式。可以是最明亮的A和B超巨星，也可能是O和F的恆星，顯示某種不可預知的小規模（尺度）脈動類型。非絕熱過程的奇怪模式逕向脈動只顯現在最明亮的超巨星。通過假設它們是低質量的後紅超巨星，低明亮的超巨星也有脈動模式，但多數的天鵝座α型變星似乎未顯現經歷過紅巨星的階段^[4][5]。

賣有可能誘發κ機制，造成鐵不透明度的變化，產生觀測上奇怪的短週期逕向和非逕向脈動方式。非絕熱的G-模式可能會產生較長的週期變化，但這些均未在天鵝座α型變星上觀測到^[6]。

列表

銀河系的

名稱	星座	發現	最大視星等 (mV)[7]	最小視星等 (mV)[7]	週期（天）	光譜類型	發光度	註解
CE Cam (HD 21389)	鹿豹座	Percy & Welsh (1983)[8]	4m.54			A0Iab	63,000[9]
CS Cam	鹿豹座		4m.259			B9Ia
大犬座η（Aludra）	大犬座	Kazarovets et al. (1999)[10]	2m.38	2m.48	4.70433	B5Ia	105,000[9]
大犬座ο2	大犬座	Waelkens et al. (1998)[3]	2m.98	3m.04	24.44	B3Ia	219,000[11]
仙后座κ	仙后座	Percy & Welsh (1983)[8]	4m.12	4m.21	2.64690	B1Ia	331,000[11]
半人馬座ο2	半人馬座		5m.12	5m.22	46.3	A2Ia	136,000[12]
仙王座ν	仙王座	Percy & Welsh (1983)[8]	4m.25	4m.35		A2 Iab	254,000[9]
南十字座DL	南十字座	Waelkens et al. (1998)[3]	6m.24	6m.28	2.8778	B1.5Ia	242,000[13]
天津四[5]	天鵝座	Lee (1910)[14]	1m.21	1m.29		A2 Ia	196,000[15]	原型
天鵝座σ	天鵝座	Abt (1957)[16]	4m.19	4m.26	120.2	B9 Iab	39,000[17]
雙子座3	雙子座	Waelkens et al. (1998)[3]	5m.75		13.70	B3 Ia	200,000[18]
獅子座ρ	獅子座	Olsen (1974)[19]	3m.83	3m.9	3.4271	B1Iab	295,000[11]
參宿七[5]	獵戶座	Waelkens et al. (1998)[3]	0m.17	0m.22	2.0748	B8Ia	279,000[20] 218,000[21]	Brightest member
ε Ori（Alnilam）	獵戶座	Cousins (1960)[22]	1m.64	1m.74	2.0748	B0.5Iabea	275,000[11] 537,000[23]
獵戶座χ2（Rigel）	獵戶座	Waelkens et al. (1998)[3]	4m.68	4m.72	2.8682	B2Ia	446,000[11]

其他星系

名稱	星系	發現	最大視星等 (mV)	最小視星等 (mV)	週期（天）	光譜類型	發光度	註解
LHA 115-S 18[24]	SMC		13m.3		複雜的	B[e]sg		可能是LBV
HDE 268835[24]	LMC		10m.60	10m.68	>100	B8p
HD 37974[24]	LMC		10m.92	11m.00	400	B0.5Ia+

參考資料

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Samus N.N., Durlevich O.V., et al. Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.)