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 编辑
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 编辑
銀河系的 编辑
| 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 编辑
| 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 编辑
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