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**天鵝座BC**
	天鵝座BC是一顆紅色的恆星（紅圈）。; 中心的明亮恒星是天津一，北面在右邊。; Credit: Erik Larsen
觀測資料; 曆元 J2000
星座	天鵝座
星官
赤經	20h 21m 38.55s
赤緯	37° 31′ 58.9″
視星等（V）	9.0 - 10.8
特性
光谱分类	M3.5 Ia (M2 - M5)
B−V 色指数	+3.13 - +3.21
变星类型	SRc
天体测定
徑向速度 (Rv)	−20.97 km/s
自行 (μ)	赤经：−3.710 mas/yr ; 赤纬：−6.307 mas/yr
视差 (π)	0.5760 ± 0.0500 mas
距离	1,710+40; −40 pc
绝对星等 (MV)	−7.71
詳細資料
質量	19 M☉
半徑	1,031 R☉
亮度	204,000 L☉
溫度	3,605 K
Minimum (1900)
半徑	1,553 R☉
亮度	145,000 L☉
溫度	2,858 K
Maximum (2000)
半徑	856 R☉
亮度	112,000 L☉
溫度	3,614 K
其他命名
	BC Cyg、HIP 100404、 HV 3339、BD+37°3903, IRAS 20197+3722、2MASS J20213855+3731589
參考資料庫
SIMBAD	资料

天鵝座BC（BC Cyg, HIP 100404, BD + 37 3903）是在天鵝座的一顆光譜類型M3.5Ia 紅超巨星和脈動變星。

它被認為是天鹅座OB1星協的成員，其中有疏散星團伯克利87（英语：Berkeley 87）^[9]，位於距離太陽系1,673秒差距（5,000光年）之處^[10]。它位於另一個紅超巨星天鵝座BI以北不到一度的地方^{[來源請求]}。根據其蓋亞目錄的視差，它的距離大約在7019524565188849422♠1,700 pc.^[1]。

計算得到天鵝座BC的有效溫度在2,858至3,614K，並且光度在112,000到145,000 L_☉之間變化。最亮和最冷時的大小被計算為1,553 R_☉，而最熱和最暗時的大小為856 R_☉。它是已知最大的恆星之一。如果它取代太陽的位置，假設最大半徑為1553 R_☉，其光球將吞噬木星的軌道。其質量約為19 M_☉，據估計，恆星質量損失，如塵埃，原子和分子氣體為每年6991320000000000000♠3.2×10⁻⁹ M_☉^[11]。

天鵝座BC的視星等在+9.0 and +10.8之間變化，週期為720 ± 40日^[2]。大約在1900年至2000年之間，它的平均亮度似乎增加了0.5星等^[4]。

參考資料

^ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 Vallenari, A.; et al. Gaia Data Release 3. Summary of the content and survey properties. Astronomy & Astrophysics. 2022. arXiv:2208.00211 . doi:10.1051/0004-6361/202243940 . 已忽略未知参数|collaboration= (帮助) Gaia DR3 record for this source at VizieR.
^ ^2.0 ^2.1 Kiss, L. L.; Szabó, Gy. M.; Bedding, T. R. Variability in red supergiant stars: Pulsations, long secondary periods and convection noise. Monthly Notices of the Royal Astronomical Society. 2006, 372 (4): 1721–1734. Bibcode:2006MNRAS.372.1721K. S2CID 5203133. arXiv:astro-ph/0608438 . doi:10.1111/j.1365-2966.2006.10973.x.
^ ^3.0 ^3.1 Samus, N. N.; Durlevich, O. V.; et al. VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013). VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 2009, 1. Bibcode:2009yCat....102025S.
^ ^4.0 ^4.1 ^4.2 ^4.3 Turner, David G.; Rohanizadegan, Mina; Berdnikov, Leonid N.; Pastukhova, Elena N. The Long-Term Behavior of the Semiregular M Supergiant Variable BC Cygni. The Publications of the Astronomical Society of the Pacific. 2006, 118 (849): 1533. Bibcode:2006PASP..118.1533T. doi:10.1086/508905 .
^ ^5.0 ^5.1 Davies, Ben; Beasor, Emma R. The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors. MNRAS. March 2020, 493 (1): 468–476. Bibcode:2020MNRAS.493..468D. S2CID 210714093. arXiv:2001.06020 . doi:10.1093/mnras/staa174 （英语）.
^ Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges. The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought. The Astrophysical Journal. 2005, 628 (2): 973–985. Bibcode:2005ApJ...628..973L. S2CID 15109583. arXiv:astro-ph/0504337 . doi:10.1086/430901.
^ Comerón, F.; Djupvik, A. A.; Schneider, N.; Pasquali, A. The historical record of massive star formation in Cygnus. Astronomy & Astrophysics. October 2020, 2009: A62. Bibcode:2020A&A...644A..62C. S2CID 221970180. arXiv:2009.12779 . doi:10.1051/0004-6361/202039188.
^ Messineo, M.; Brown, A. G. A. A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2. The Astronomical Journal. 2019, 158 (1): 20. Bibcode:2019AJ....158...20M. S2CID 148571616. arXiv:1905.03744 . doi:10.3847/1538-3881/ab1cbd.
^ Sokal, Kimberly R.; Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner. Chandra Detects the Rare Oxygen-type Wolf-Rayet Star WR 142 and OB Stars in Berkeley 87. The Astrophysical Journal. 2010, 715 (2): 1327. Bibcode:2010ApJ...715.1327S. S2CID 119232391. arXiv:1004.0462 . doi:10.1088/0004-637X/715/2/1327.
^ de la Fuente, Diego; Román-Zúñiga, Carlos G.; Jiménez-Bailón, Elena; Alves, João; Garcia, Miriam; Venus, Sean. Clustered star formation toward Berkeley 87/ON2. I. Multiwavelength census and the population overlap problem. Astronomy and Astrophysics. 2021, 650: A156. Bibcode:2021A&A...650A.156D. S2CID 232170603. arXiv:2103.06062 . doi:10.1051/0004-6361/202040065.
^ Josselin, E.; Plez, B. Atmospheric dynamics and the mass loss process in red supergiant stars. Astronomy and Astrophysics. 2007, 469 (2): 671. Bibcode:2007A&A...469..671J. S2CID 17789027. arXiv:0705.0266 . doi:10.1051/0004-6361:20066353.
^ Download Data. aavso.org. AAVSO. [1 October 2021]. （原始内容存档于2023-03-15）.