M18 (疏散星團)

M18（梅西耶18）
	人馬座的疏散星團。
觀測資料 (J2000.0 曆元)
赤經	18h 19m 58.0s
赤緯	–17° 06′ 06″
距離	4.23 kly（1.296 kpc）
視星等 (V)	7.5
視大小 (V)	9.8′
物理特徵
質量	186+161; −86 M☉
半徑	26.2光年
估計年齡	33×106 年
其他特徵	梅西耶 18, NGC 6613, Cr 376, OCl 40
	相關條目：疏散星團、NGC天體表

M18或梅西耶18，也稱為NGC 6613，是在人馬座的一個疏散星團。它是梅西耶在1764年發現，並被列入它的類似彗星天體的清單中^[8]。從地球的位置來看，M18位於歐米茄星雲和人馬座恆星雲（M24）之間^[3]。

這是一個稀疏的^[9]星團，實直徑大約8秒差距^[5]，潮汐半徑大約7.3秒差距^[6]，恆星集中的核心半徑為0.012秒差距^[10]。它的川普勒分類是II 3 p^[4]。M18的年齡約為3,300萬年^[6]，質量估計為7032373847400000000♠188 M_☉^[5]。它擁有一顆Be星和總共29顆B型星^[9]。有三顆超巨星，都是 A型或早期型^[11]。最亮的一顆（盧西達）是HD 168352，光譜類型是B2III，視星等+8.65 ^[4]。

M18距離地球1,296秒差距^[2]，距離銀河中心6,830秒差距^[5]。它圍繞銀河核心運行的週期為1.865億年，離心率為0.02。這使它可以接近銀河中心至6,500秒差距，或遠離至6,800秒差距。它約每2,740萬年會穿越銀河盤面一次，而在盤面上下方的垂直距離不會超過80秒差距^[1]

圖集[編輯]

來自2微米全天巡天項目的M18照片。
顯示M18位置的星圖（Roberto Mura）
奧米加望遠鏡（英語：VLT Survey Telescope# OmegaCAM）拍攝的M18（左上）及其周圍環境。^[12]

參考資料[編輯]

^ ^1.0 ^1.1 ^1.2 Wu, Zhen-Yu; et al, The orbits of open clusters in the Galaxy, Monthly Notices of the Royal Astronomical Society, November 2009, 399 (4): 2146–2164, Bibcode:2009MNRAS.399.2146W, arXiv:0909.3737 , doi:10.1111/j.1365-2966.2009.15416.x.
^ ^2.0 ^2.1 Kharchenko, N. V.; et al, Astrophysical parameters of Galactic open clusters, Astronomy and Astrophysics, 2005, 438 (3): 1163–1173, Bibcode:2005A&A...438.1163K, arXiv:astro-ph/0501674 , doi:10.1051/0004-6361:20042523.
^ ^3.0 ^3.1 Frommert, Hartmut; Kronberg, Christine, Messier 18, Students for the Exploration and Development of Space (SEDS), August 21, 2007 [2018-11-11], （原始內容存檔於2018-10-04）.
^ ^4.0 ^4.1 ^4.2 Lindoff, U., The open clusters NGC 6613 (M 18) and NGC 6716, Astronomy and Astrophysics, December 1971, 15: 439–449, Bibcode:1971A&A....15..439L.
^ ^5.0 ^5.1 ^5.2 ^5.3 ^5.4 Joshi, Y. C.; et al, Study of open clusters within 1.8 kpc and understanding the Galactic structure, Astronomy & Astrophysics, October 2016, 593: 13, Bibcode:2016A&A...593A.116J, arXiv:1606.06425 , doi:10.1051/0004-6361/201628944, A116.
^ ^6.0 ^6.1 ^6.2 Piskunov, A. E.; et al, Tidal radii and masses of open clusters, Astronomy and Astrophysics, January 2008, 477 (1): 165–172, Bibcode:2008A&A...477..165P, doi:10.1051/0004-6361:20078525 .
^ M 18. SIMBAD. 斯特拉斯堡天文資料中心.
^ Adam, Len, Imaging the Messier Objects Remotely from Your Laptop, The Patrick Moore Practical Astronomy Series, Springer: 117–120, 2018, Bibcode:2018imor.book.....A, ISBN 978-3319653853.
^ ^9.0 ^9.1 McSwain, M. Virginia; Gies, Douglas R., The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters, The Astrophysical Journal Supplement Series, November 2005, 161 (1): 118–146, Bibcode:2005ApJS..161..118M, arXiv:astro-ph/0505032 , doi:10.1086/432757.
^ Santos-Silva, T.; Gregorio-Hetem, J., Characterisation of young stellar clusters, Astronomy & Astrophysics, November 6, 2012, 547: A107, Bibcode:2012A&A...547A.107S, arXiv:1209.1585 , doi:10.1051/0004-6361/201219695.
^ Eggenberger, P.; et al, The blue to red supergiant ratio in young clusters at various metallicities, Astronomy and Astrophysics, May 2002, 386 (2): 576–582, Bibcode:2002A&A...386..576E, arXiv:astro-ph/0202478 , doi:10.1051/0004-6361:20020262.
^ Stellar Lab in Sagittarius, www.eso.org, [11 August 2016], （原始內容存檔於2020-10-19）.

外部連結[編輯]

WikiSky上關於M18 (疏散星團)的內容：DSS2, SDSS, GALEX, IRAS, 氫α, X射線, 天文照片, 天圖, 文章和圖片

天球赤道座標： 18^h 19^m 54^s，−17° 07′ 60″

[Wu2009-1] 1.0 ^1.1 ^1.2 Wu, Zhen-Yu; et al, The orbits of open clusters in the Galaxy, Monthly Notices of the Royal Astronomical Society, November 2009, 399 (4): 2146–2164, Bibcode:2009MNRAS.399.2146W, arXiv:0909.3737 , doi:10.1111/j.1365-2966.2009.15416.x.

[kharchenko2005-2] 2.0 ^2.1 Kharchenko, N. V.; et al, Astrophysical parameters of Galactic open clusters, Astronomy and Astrophysics, 2005, 438 (3): 1163–1173, Bibcode:2005A&A...438.1163K, arXiv:astro-ph/0501674 , doi:10.1051/0004-6361:20042523.

[Frommert2007-3] 3.0 ^3.1 Frommert, Hartmut; Kronberg, Christine, Messier 18, Students for the Exploration and Development of Space (SEDS), August 21, 2007 [2018-11-11], （原始內容存檔於2018-10-04）.

[Lindoff1971-4] 4.0 ^4.1 ^4.2 Lindoff, U., The open clusters NGC 6613 (M 18) and NGC 6716, Astronomy and Astrophysics, December 1971, 15: 439–449, Bibcode:1971A&A....15..439L.

[Joshi2016-5] 5.0 ^5.1 ^5.2 ^5.3 ^5.4 Joshi, Y. C.; et al, Study of open clusters within 1.8 kpc and understanding the Galactic structure, Astronomy & Astrophysics, October 2016, 593: 13, Bibcode:2016A&A...593A.116J, arXiv:1606.06425 , doi:10.1051/0004-6361/201628944, A116.

[Piskunov2008-6] 6.0 ^6.1 ^6.2 Piskunov, A. E.; et al, Tidal radii and masses of open clusters, Astronomy and Astrophysics, January 2008, 477 (1): 165–172, Bibcode:2008A&A...477..165P, doi:10.1051/0004-6361:20078525 .

[SIMBAD-7] M 18. SIMBAD. 斯特拉斯堡天文資料中心.

[Adam2018-8] Adam, Len, Imaging the Messier Objects Remotely from Your Laptop, The Patrick Moore Practical Astronomy Series, Springer: 117–120, 2018, Bibcode:2018imor.book.....A, ISBN 978-3319653853.

[McSwain2005-9] 9.0 ^9.1 McSwain, M. Virginia; Gies, Douglas R., The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters, The Astrophysical Journal Supplement Series, November 2005, 161 (1): 118–146, Bibcode:2005ApJS..161..118M, arXiv:astro-ph/0505032 , doi:10.1086/432757.

[Silva2012-10] Santos-Silva, T.; Gregorio-Hetem, J., Characterisation of young stellar clusters, Astronomy & Astrophysics, November 6, 2012, 547: A107, Bibcode:2012A&A...547A.107S, arXiv:1209.1585 , doi:10.1051/0004-6361/201219695.

[Eggenberger2002-11] Eggenberger, P.; et al, The blue to red supergiant ratio in young clusters at various metallicities, Astronomy and Astrophysics, May 2002, 386 (2): 576–582, Bibcode:2002A&A...386..576E, arXiv:astro-ph/0202478 , doi:10.1051/0004-6361:20020262.

[eso2016-12] Stellar Lab in Sagittarius, www.eso.org, [11 August 2016], （原始內容存檔於2020-10-19）.

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圖集[編輯]

相關條目[編輯]

參考資料[編輯]

外部連結[編輯]