恆星系統

恆星系統或恆星系是少數幾顆恆星受到引力的拘束而互相環繞的系統^[1]，為數眾多的恆星受到引力的約束一般稱為“星團”或“星系”，但是概括來說都可以稱為恆星系統。恆星系統有時也會用在單獨但有更小的行星系環繞的恆星^[2]^[3]。

聯星系統[编辑]

主条目：聯星

由兩顆恆星組成的恆星系統稱為聯星、聯星系統或物理雙星。如果沒有潮汐效應、其它力量的攝動、和從一顆恆星至另一顆恆星的質量的傳輸，這樣的系統是穩定的，並且兩顆星會在以質心為焦點的橢圓軌道上互繞著 (參見二體問題) 。

聯星的例子有天狼星、南河三和天鵝座X-1，而最後的這個可能是一個黑洞。

聚星系統[编辑]

聚星或物理聚星是超過兩顆以上恆星組成的系統^[4]^[5]。聚星系統如果由三顆恆星組成，就稱為三合星、三重星或三元星；四顆星的系統稱為四重星或四合星；五顆星組成的稱為五重星；六顆星組成的稱為六重星；七顆星組成的稱為七重星，依此類推。這些系統都遠小於有100至1,000顆恆星，動力學系統更複雜的疏散星團^[6]。

動力學[编辑]

理論上，模擬一個聚星系統比模擬聯星系統更困難，當多體問題的動力系統介入時，可能呈現渾沌的行為。許多小集團的恆星被發現是不穩定的，一旦發生一顆星與另一顆星過度的接近，便會發生加速而會從系統中逃逸掉^[7]。如果這個系統出現埃文斯所謂的階式模型^[8]，還是有可能穩定。在階式模型系統內，恆星被分成兩個小集團，各自在較大的軌道上繞著共同的質心運轉；每個小集團也都是階式模型，意味著小集團又必需再分為更小的次集團，而且一直如此的細分下去。在這樣的情況下，各個恆星的運動將持續的以接近穩定的軌道，遵循克卜勒的軌道繞著系統的質量中心^[9]。不同於擁有數量龐大恆星，且動力學系統更為複雜的星系和星團。

藝術家臆測的HD 188753軌道，是一個三合星系統。

觀測[编辑]

許多已知的聚星系統都是三合星；更多星的聚星系統則隨著恆星數量的增加而呈指數性的減少^[10]。例如，在1999年修訂的Tokovinin目錄^[5]中列出的物理聚星， 728個系統中有551個是三合星。但是因為選擇效應，我們在這些知識上的統計常是殘缺不全的^[11]^, §2.。

由於前面提到在動力學上的不穩定，三合星通常都是階式模型：它們包含兩顆靠近的聯星對和一顆距離較遠的伴星。有著更多恆星的聚星系統也都是階式模型。^[10]目前所知最多的是六重星系統，例如北河二（雙子座α），它是一對聯星以更遠的距離繞著另一對各自也是聯星的聯星系統^[12]。另一個六顆星的系統是ADS 9731，它由兩對三合星組成，每一對都是伴隨著一顆單獨恆星在軌道上運轉的光譜聯星^[13]。

例子[编辑]

聯星[编辑]

天狼星：包含一顆A-型主序星和白矮星的聯星。
御夫座ε：一組食雙星。

三合星[编辑]

北極星：北極星是一組三合星，主星是靠得很近的一對聯星—近得在2006年被哈柏太空望遠鏡拍到之前只能從對主星的重力拖曳上察覺到。
半人馬座α：是一組由兩顆黃矮星（半人馬座αA和半人馬座αB）組成的聯星為主的三合星，另一顆遠離的紅矮星就是比鄰星。A和B是物理聯星，在一個最近距離11天文單位，最遠距離36天文單位的離心軌道上互繞；比鄰星在非常遙遠的距離（～15,000天文單位）與A和B互繞著。但是這個距離相較於其他的恆星仍是非常的近，也仍然受到A和B的引力拘束著^[14]。
HD 188753是位於天鵝座，距離地球149光年遠的三合星系統。這個系統由黃矮星HD 188753 A、橙矮星HD 188753 B、和紅矮星HD 188753 C組成；B和C成一個集團以156天的週期互繞，A的軌道週期則為25.7年。

四合星[编辑]

半人馬4^[15]
開陽：曾經是第一對聯星，在1650年就被Giovanni Battista Riccioli發現^[16]^, p. 1;,^[17]，但它可能在更早就被伽利略和Benedetto Castelli觀測過。後來，光譜學揭露開陽A和開陽B本身也都是聯星^[18]。
HD 98800

五重星[编辑]

天蠍座ν：由靠得很近，相距41弧秒的兩群恆星組成的五重星。^[19]
91 Aquarii
參宿三

六重星[编辑]

北河二（雙子座α）^[12]
ADS 9731^[13]

参考文献[编辑]

^ "Star system" in Modern Dictionary of Astronomy and Space Technology. A.S. Bhatia, ed. New Delhi: Deep & Deep Publications, 2005. ISBN 81-7629-741-0
^ Astronomers discover a nearby star system just like our own Solar System, Joint Astronomy Centre, press release, July 8, 1998. Accessed on line September 23, 2007.
^ Life unlikely in asteroid-ridden star system, Maggie McKee, NewScientist.com news service, July 7 2004. Accessed on line September 23, 2007.
^ p. 16, Understanding Variable Stars, John R. Percy, Cambridge: Cambridge University Press, 2007, ISBN 0-521-23253-8.
^ ^5.0 ^5.1 MSC—a catalogue of physical multiple stars, A. A. Tokovinin, Astronomy and Astrophysics Supplement Series 124 (1997), 75–84; online versions at VizieR and the Multiple Star Catalog.
^ p. 24, Galactic Dynamics, James Binney and Scott Tremaine, Princeton University Press, 1987, ISBN 0-691-08445-9.
^ Multiple Stellar Systems: Types and Stability, Peter J. T. Leonard, in Encyclopedia of Astronomy and Astrophysics, P. Murdin, ed., online edition at the Institute of Physics, orig. ed. published by Nature Publishing Group, 2001.
^ Stars of Higher Multiplicity, David S. Evans, Quarterly Journal of the Royal Astronomical Society 9 (1968), 388–400.
^ Dynamics of multiple stars: observations, A. Tokovinin, in "Massive Stars in Interacting Binaries", August 16–20, 2004, Quebec (ASP Conf. Ser., in print).
^ ^10.0 ^10.1 Statistics of multiple stars: some clues to formation mechanisms, A. Tokovinin, in the proceedings of IAU Symposium 200, The Formation of Binary Stars, Potsdam, Germany, April 10–15, 2000. Bibcode 2001IAUS..200...84T.
^ Statistics of multiple stars, A. Tokovinin, in The Environment and Evolution of Double and Multiple Stars, Proceedings of IAU Colloquium 191, held 3-7 February, 2002 in Merida, Yucatan, Mexico, edited by Christine Allen and Colin Scarfe, Revista Mexicana de Astronomía y Astrofísica（Serie de Conferencias）21 (August 2004), pp. 7–14.
^ ^12.0 ^12.1 Castor A and Castor B resolved in a simultaneous Chandra and XMM-Newton observation, B. Stelzer and V. Burwitz, Astronomy and Astrophysics 402 (May 2003), pp. 719–728.
^ ^13.0 ^13.1 ADS 9731: A new sextuple system, A. A. Tokovinin, N. I. Shatskii, and A. K. Magnitskii, Astronomy Letters, 24, #6 (November 1998), pp. 795–801.
^ Are Proxima and α Centauri Gravitationally Bound?, Jeremy G. Wertheimer, Gregory Laughlin, Astronomical Journal 132, #5 (November 2006), pp. 1995–1997.
^ 4 Centauri, entry in the Multiple Star Catalog.
^ The Binary Stars, R. G. Aitken, New York: Semi-Centennial Publications of the University of California, 1918.
^ Vol. 1, part 1, p. 422, Almagestum Novum, Giovanni Battista Riccioli, Bononiae: Ex typographia haeredis Victorij Benatij, 1651.
^ A New View of Mizar, Leos Ondra, accessed on line May 26, 2007.
^ Nu Scorpii, entry in the Multiple Star Catalog.

外部鏈接[编辑]

参见[编辑]

[1] "Star system" in Modern Dictionary of Astronomy and Space Technology. A.S. Bhatia, ed. New Delhi: Deep & Deep Publications, 2005. ISBN 81-7629-741-0

[2] Astronomers discover a nearby star system just like our own Solar System, Joint Astronomy Centre, press release, July 8, 1998. Accessed on line September 23, 2007.

[3] Life unlikely in asteroid-ridden star system, Maggie McKee, NewScientist.com news service, July 7 2004. Accessed on line September 23, 2007.

[4] . 16, Understanding Variable Stars, John R. Percy, Cambridge: Cambridge University Press, 2007, ISBN 0-521-23253-8.

[tokc-5] 5.0 ^5.1 MSC—a catalogue of physical multiple stars, A. A. Tokovinin, Astronomy and Astrophysics Supplement Series 124 (1997), 75–84; online versions at VizieR and the Multiple Star Catalog.

[6] . 24, Galactic Dynamics, James Binney and Scott Tremaine, Princeton University Press, 1987, ISBN 0-691-08445-9.

[7] Multiple Stellar Systems: Types and Stability, Peter J. T. Leonard, in Encyclopedia of Astronomy and Astrophysics, P. Murdin, ed., online edition at the Institute of Physics, orig. ed. published by Nature Publishing Group, 2001.

[8] Stars of Higher Multiplicity, David S. Evans, Quarterly Journal of the Royal Astronomical Society 9 (1968), 388–400.

[9] Dynamics of multiple stars: observations, A. Tokovinin, in "Massive Stars in Interacting Binaries", August 16–20, 2004, Quebec (ASP Conf. Ser., in print).

[tok1-10] 10.0 ^10.1 Statistics of multiple stars: some clues to formation mechanisms, A. Tokovinin, in the proceedings of IAU Symposium 200, The Formation of Binary Stars, Potsdam, Germany, April 10–15, 2000. Bibcode 2001IAUS..200...84T.

[11] Statistics of multiple stars, A. Tokovinin, in The Environment and Evolution of Double and Multiple Stars, Proceedings of IAU Colloquium 191, held 3-7 February, 2002 in Merida, Yucatan, Mexico, edited by Christine Allen and Colin Scarfe, Revista Mexicana de Astronomía y Astrofísica（Serie de Conferencias）21 (August 2004), pp. 7–14.

[castor-12] 12.0 ^12.1 Castor A and Castor B resolved in a simultaneous Chandra and XMM-Newton observation, B. Stelzer and V. Burwitz, Astronomy and Astrophysics 402 (May 2003), pp. 719–728.

[ads9731-13] 13.0 ^13.1 ADS 9731: A new sextuple system, A. A. Tokovinin, N. I. Shatskii, and A. K. Magnitskii, Astronomy Letters, 24, #6 (November 1998), pp. 795–801.

[14] Are Proxima and α Centauri Gravitationally Bound?, Jeremy G. Wertheimer, Gregory Laughlin, Astronomical Journal 132, #5 (November 2006), pp. 1995–1997.

[15] 4 Centauri, entry in the Multiple Star Catalog.

[16] The Binary Stars, R. G. Aitken, New York: Semi-Centennial Publications of the University of California, 1918.

[17] Vol. 1, part 1, p. 422, Almagestum Novum, Giovanni Battista Riccioli, Bononiae: Ex typographia haeredis Victorij Benatij, 1651.

[mizar-18] A New View of Mizar, Leos Ondra, accessed on line May 26, 2007.

[19] Nu Scorpii, entry in the Multiple Star Catalog.

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