NGC 6441

NGC 6441
NGC 6441
觀測數據(J2000 曆元)
星座	天蠍座
赤經	17h 50m 13.06s
赤緯	−37° 03′ 05.2″
距離	44 kly（13.5 kpc）
視星等 (V)	7.2
視直徑(V)	9.6′
物理性質
Mass	1.6×106 M☉
金屬量	−0.53 dex
估計年齡	13−13.7 Gyr
	參見：球狀星團，球狀星團表

NGC 6441位於南天的天蠍座，是登錄在NGC天體表內的一個球狀星團。它是蘇格蘭的天文學家詹姆士·敦洛普在1826年5月13日發現的。根據敦洛普的描述，這是一個小，但有明確界線的明亮星雲，直徑大約20″。這個星團位於傅說 (恆星)（天蠍座 G）東北東方5弧分^[3]，與太陽相距約44,000光年 ^[2]。

這是銀河系中最大和最明亮的球狀星團之一，估計質量是160萬倍太陽質量。它位於銀河系的核球，距離銀心約13 kly（3.9 kpc）^[6]，被認為是富金屬量。也就是相對之下有較多高於氦元素的金屬元素豐度^[4]。相較於0.64弧分的半質量半徑，星團的核心區域大約是0.11弧分。在核心區域的恆星密度暗示它的亮度密度是5.25 L_⊙ pc⁻³^[2]。星團的半光度半徑是7.1 ly（2.18 pc）^[6]。

這個星團有異常大量的天琴座RR變星，在2006年時有68顆候選者，並且週期長於各自金屬豐度範圍的典型（星團的RRab星的平均週期是0.759天）。它也有幾顆第二型造父變星，在這個星團內有不尋常的高金屬量^[7]。在顏色-星等圖的紅巨星分支章節解釋，星團中至少有兩種，並可能有三種不同的星族。最亮和較高溫的紅群聚星族集中在星團的中心。這個集團可能是富含氦的第二族恆星^[8]。

這個星團內至少有4顆毫秒脈衝星，且其中兩顆是在聯星系。其中一顆是軌道離心率高達0.71的聯星PSR J1750−37A^[2]。這個星團有一顆X射線爆發源，X1746-370，它有著在所有的球狀團和星系中已知最長的週期^[9]。最後，這而還有一個行星狀星雲，JaFu 2^[10]，是在銀河系內已知有行星狀星雲的4個球狀星團之一^[3]。

參考資料

^ ^1.0 ^1.1 Goldsbury, Ryan; et al, The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters, The Astronomical Journal, December 2010, 140 (6): 1830–1837, Bibcode:2010AJ....140.1830G, arXiv:1008.2755 , doi:10.1088/0004-6256/140/6/1830.
^ ^2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Freire, Paulo C. C.; et al, Eight New Millisecond Pulsars in NGC 6440 and NGC 6441, The Astrophysical Journal, March 2008, 675 (1): 670−682, Bibcode:2008ApJ...675..670F, arXiv:0711.0925 , doi:10.1086/526338.
^ ^3.0 ^3.1 ^3.2 ^3.3 O'Meara, Stephen James, Deep-Sky Companions: Southern Gems, Cambridge University Press: 360−363, 2013 [2016-09-16], ISBN 1139851543, （原始內容存檔於2016-05-03）
^ ^4.0 ^4.1 Bellini, A.; et al, The Intriguing Stellar Populations in the Globular Clusters NGC 6388 and NGC 6441, The Astrophysical Journal, March 2013, 765 (1): 27, Bibcode:2013ApJ...765...32B, arXiv:1301.2822 , doi:10.1088/0004-637X/765/1/32, 32.
^ Leaman, Ryan, Insights into Pre-enrichment of Star Clusters and Self-enrichment of Dwarf Galaxies from Their Intrinsic Metallicity Dispersions, The Astronomical Journal, December 2012, 144 (6): 13, Bibcode:2012AJ....144..183L, arXiv:1209.4648 , doi:10.1088/0004-6256/144/6/183, 183.
^ ^6.0 ^6.1 ^6.2 Mackey, A. D.; van den Bergh, Sidney, The properties of Galactic globular cluster subsystems, Monthly Notices of the Royal Astronomical Society, June 2005, 360 (2): 631−645, Bibcode:2005MNRAS.360..631M, arXiv:astro-ph/0504142 , doi:10.1111/j.1365-2966.2005.09080.x.
^ Corwin, T. Michael; et al, Image-Subtraction Photometry of Variable Stars in the Globular Clusters NGC 6388 and NGC 6441, The Astronomical Journal, September 2006, 132 (3): 1014−1022, Bibcode:2006AJ....132.1014C, arXiv:astro-ph/0605569 , doi:10.1086/505745.
^ Krogsrud, David A.; et al, The Curious Radial Distributions of Horizontal Branch Stars in NGC 6441, The Astrophysical Journal Letters, April 2013, 767 (2): 5, Bibcode:2013ApJ...767L..27K, arXiv:1304.1470 , doi:10.1088/2041-8205/767/2/L27, L27.
^ Homer, L.; et al, Optical Identification of the X-Ray Burster X1746-370 in the Globular Cluster NGC 6441, The Astronomical Journal, June 2002, 123 (6): 3255−3262, Bibcode:2002AJ....123.3255H, arXiv:astro-ph/0201550 , doi:10.1086/340470.
^ Jacoby, George H.; et al, Planetary Nebulae in the Globular Cluster PAL 6 and NGC 6441, Astronomical Journal, December 1997, 114: 2611, Bibcode:1997AJ....114.2611J, doi:10.1086/118671.

[aj140_6_1830-1] 1.0 ^1.1 Goldsbury, Ryan; et al, The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters, The Astronomical Journal, December 2010, 140 (6): 1830–1837, Bibcode:2010AJ....140.1830G, arXiv:1008.2755 , doi:10.1088/0004-6256/140/6/1830.

[apj675_1_670-2] 2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Freire, Paulo C. C.; et al, Eight New Millisecond Pulsars in NGC 6440 and NGC 6441, The Astrophysical Journal, March 2008, 675 (1): 670−682, Bibcode:2008ApJ...675..670F, arXiv:0711.0925 , doi:10.1086/526338.

[omeara2013-3] 3.0 ^3.1 ^3.2 ^3.3 O'Meara, Stephen James, Deep-Sky Companions: Southern Gems, Cambridge University Press: 360−363, 2013 [2016-09-16], ISBN 1139851543, （原始內容存檔於2016-05-03）

[apj765_1_32-4] 4.0 ^4.1 Bellini, A.; et al, The Intriguing Stellar Populations in the Globular Clusters NGC 6388 and NGC 6441, The Astrophysical Journal, March 2013, 765 (1): 27, Bibcode:2013ApJ...765...32B, arXiv:1301.2822 , doi:10.1088/0004-637X/765/1/32, 32.

[aj144_6_183-5] Leaman, Ryan, Insights into Pre-enrichment of Star Clusters and Self-enrichment of Dwarf Galaxies from Their Intrinsic Metallicity Dispersions, The Astronomical Journal, December 2012, 144 (6): 13, Bibcode:2012AJ....144..183L, arXiv:1209.4648 , doi:10.1088/0004-6256/144/6/183, 183.

[mnras360_2_631-6] 6.0 ^6.1 ^6.2 Mackey, A. D.; van den Bergh, Sidney, The properties of Galactic globular cluster subsystems, Monthly Notices of the Royal Astronomical Society, June 2005, 360 (2): 631−645, Bibcode:2005MNRAS.360..631M, arXiv:astro-ph/0504142 , doi:10.1111/j.1365-2966.2005.09080.x.

[aj132_3_1014-7] Corwin, T. Michael; et al, Image-Subtraction Photometry of Variable Stars in the Globular Clusters NGC 6388 and NGC 6441, The Astronomical Journal, September 2006, 132 (3): 1014−1022, Bibcode:2006AJ....132.1014C, arXiv:astro-ph/0605569 , doi:10.1086/505745.

[ajl767_2_L27-8] Krogsrud, David A.; et al, The Curious Radial Distributions of Horizontal Branch Stars in NGC 6441, The Astrophysical Journal Letters, April 2013, 767 (2): 5, Bibcode:2013ApJ...767L..27K, arXiv:1304.1470 , doi:10.1088/2041-8205/767/2/L27, L27.

[aj123_6_3255-9] Homer, L.; et al, Optical Identification of the X-Ray Burster X1746-370 in the Globular Cluster NGC 6441, The Astronomical Journal, June 2002, 123 (6): 3255−3262, Bibcode:2002AJ....123.3255H, arXiv:astro-ph/0201550 , doi:10.1086/340470.

[aj114_2611-10] Jacoby, George H.; et al, Planetary Nebulae in the Globular Cluster PAL 6 and NGC 6441, Astronomical Journal, December 1997, 114: 2611, Bibcode:1997AJ....114.2611J, doi:10.1086/118671.

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