天鵝座X

天鵝座X是在星座天鹅座北部的一顆變星，英文縮寫為X Cyg。這是一顆仙王座δ型變星，其視星等的亮度範圍從5.85到6.91的，週期為16.386332天。在最亮的時候，這顆恆星肉眼隱約可見。根據視差的量測，到這顆恆星的距離約為628光年。它正以8.1km/s的徑向速度遠離我們。這顆恆星很可能是疏散星團魯普雷希特173（英语：Ruprecht 173）的成員。 這顆恆星的變星光度是由小賽斯·卡羅·錢德勒於1886年發現的。在1907年，埃德溫·布蘭特·弗羅斯特（英语：Edwin Brant Frost）表明，天鵝座X是一顆F型恆星，具有不同的徑向速度，其行為類似於仙王座δ變星。米歇爾·路易澤（英语：Michel Luizet）在1912年發現，這種變化的週期為16.38543天。在1919年，弗蘭克·克雷格·喬丹（英语：Frank Craig Jordan）確定恆星的色指數在每個週期中都會發生變化，隨著恆星變暗而變紅。它被確定為滿足簡單周光關係的基準恆星類別經典造父變星的成員。 在1954年，羅伯特·克拉夫特在峰值亮度下發現其恆星分類為F7-Ib，與F型超巨星的光譜相匹配。這顆恆星的光譜類型在脈動週期中變化，在最小亮度下低至G8 Ib。在1956年，克拉夫特發現某些譜線加倍，他解釋說這是由於之前的脈動週期中，物質殼下落與光球碰撞的結果。與大多數造父變星在每個週期經歷一次衝擊不同，天鹅座X被發現經歷了一次雙重衝擊。 現時還沒有發現軌道週期在十年或更短的伴星。這顆恆星顯示出卷雲，並初步證明了紅外的長期發射。 MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, [30 December 2022], （原始内容存档于2023-03-27）.  Brown, A. G. A.; et al. Gaia Early Data Release 3: Summary of the contents and survey properties. Astronomy & Astrophysics. 2021, 649: A1. Bibcode:2021A&A...649A...1G. 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