五車二

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五車二 Aa/Ab
Auriga constellation map.png
五車二是御夫座內最亮的恆星
觀測資料
Epoch J2000.0      Equinox J2000.0 (ICRS)
星座 御夫座
Component Aa Ab
赤經 05h 16m 41.3591s[1][note 1]
赤緯 +45° 59′ 52.768″[1][note 1]
視星等 (V) 0.91[2][note 2] 0.76[2][note 2]
  0.08   
(0.03 to 0.16)[1][3]
特徵
光譜類型 G8III/K0III[4] G1III[4]
U-B 色指數 +0.44[5]
B-V 色指數 +0.80[5]
V-R 色指數 −0.3[1]
R-I 色指數 +0.44[5]
變星類型 猎犬座RS型变星[1]
天體測量
徑向速度 (Rv) 29.19 ± 0.074[6][note 3] km/s
自行:  
赤經 α cos δ) 75.52[1][note 1] mas/yr
Dec. δ) −427.11[1][note 1] mas/yr
視差 (π) 77.29 ± 0.89[1] mas
距離 42.2 ± 0.5 ly
(12.9 ± 0.1 pc)
絕對星等 (MV) 0.35[note 4] 0.20[note 4]
  −0.48[note 4]
Details
質量 2.69 ± 0.06[4] M 2.56 ± 0.04[4] M
半徑 12.2 ± 0.2[4] R 9.2 ± 0.4[4] R
光度 (bolometric) 78.5 ± 1.2[4] L 77.6 ± 2.6[4] L
溫度 4940 ± 50[4] K 5700 ± 100[4] K
金屬量 40% Sun[note 5]
自轉 106 ± 3 d [7] 8.64 ± 0.09 d [7]
自轉速度 (v sin i) 3[8]km/s 36[8]km/s
年齡 5.2 × 108  [4]
軌道[4]
週期 (P) 104.022 ± 0.002 d
半長軸 (a) 56.47 ± 0.05 mas
離心率 (e) 0.0000 ± 0.0002
傾角 (i) 137.18 ± 0.05°
經度交點 (Ω) 40.8 ± 0.1°
近星點 曆元 (T) 2447528.45 ± 0.02 JD
Database references
SIMBAD data
  data data
其他名稱
Alhajoth, Capella, Hokulei, 御夫座α, α Aur, Alpha Aurigae, Alpha Aur, 13 Aurigae, 13 Aur, ADS 3841 AP, BD+45°1077, CCDM J05168+4559AP, FK5 193, GC 6427, GJ 194, HD 34029, HIP 24608, HR 1708, IDS 05093+4554 AP, LTT 11619, NLTT 14766, PPM 47925, SAO 40186, WDS 05167+4600Aa/Ab.[1][5][9][10]

五車二 ( α Aur / 御夫座α)是御夫座內最亮的一顆恆星,並且是全天第6亮星,排在大角織女之後,是北半球的第3亮星。雖然,以肉眼看它只是一顆單獨的星,但它其實是個恆星系統,由4顆恆星組成兩對聯星。第一對包括兩顆亮星,大的一顆恆星光譜是G-型巨星,兩顆恆星半徑大約都是太陽的10倍,在靠得很近的軌道上互繞著。這兩顆星被認為是冷卻並在膨脹中的紅巨星。第二對與第一對相距大約11,000天文單位 (0.17光年),由兩顆較小且較暗的恆星組成,被認為是兩顆紅矮星[11][12]。五車二的系統相對來說非常靠近地球,距離只有42.2光年(12.9秒差距)。

系統[编辑]

五車二的系統包含一對由明亮的巨星組成的聯星,和另一對較暗且在相同距離外一起環繞的紅矮星[12]。這個系統屬於畢宿移動星群[5][13],是與畢宿星團有著相同移動方向的一些恆星組成的。[5][14]

亮聯星對[编辑]

在1899年,基于分光镜的观测,五车二第一次被宣布是一颗双星。[15][16] 五车二素以“干涉测量学家之友”著称,该双星系统在1919年由威尔逊山天文台约翰·安德森弗朗西斯·皮斯首次进行了分解。基于他们的观测,它们的轨道在1920年得以公布。[17][18] 这是首次对在太阳系以外的天体进行干涉测量。[19] 基于威尔逊山天文台的Mark III的干涉测量,五车二双星系统的高精度轨道在1994年发表。[4] 1995年9月,剑桥成像光学孔径综合望远镜通过独立元素光学干涉仪拍摄了五车二的影像,这是第一个通过该方法拍摄的天体。[20]

五车二由两颗G光谱型的巨星组成。主星表面温度约4900K,半径约为12个太阳半径,质量约为2.7个太阳质量,全波段的光度约为太阳的79倍。伴星温度约为5700K,半径约为9个太阳半径,质量约为2.6个太阳质量,全波段的光度约为太阳的78倍。[4] 如果考察全部波段辐射,该恒星系统的主星更加明亮;但在可见光波段观测时,主星却更加暗淡:主星的视星等约为0.91,而伴星视星等为0.76。[4]

该联星对并非食双星,也就是说,从地球上看,二者从不互相遮挡。它们的绕行轨道直径约1亿千米,绕行周期约为104天。它们在主序星阶段可能类似于织女星,为A光谱型;现在它们正在膨胀变冷,成为越来越亮的红巨星,这一阶段大概要花费数百万年时间。人们猜想,二者中质量更大的恒星在其核心已经开始进行氦聚变,产生碳和氧;但这个过程在质量较小者身上还没有进行。[21]

X射线源[编辑]

分别在1962年9月20日和1963年3月15日发射的两支Aerobee高空探测火箭在位于御夫座赤经05h09m赤纬+45°的地方探测到显著的X射线源。[22] 五车二被确认在误差范围内。[22]

恒星X射线天文学起源于1974年4月5日对五车二的X射线探测。[23] 那天进行了一次校准火箭飞行姿态控制,恒星传感器把有效载荷轴指向五车二(α Aur)。这期间,X射线反射系统和恒星传感器共同探测到了范围为0.2—1.6 keV的X射线。[23] 这次X射线的光度(Lx) 的数量级为~1024 W (1031 erg s−1),这比太阳X射线光度要高4个数量级。[23]

五车二是一个X射线源,这被认为主要源于更大质量恒星的日冕层。[24] 五车二是ROSAT X射线源1RXS J051642.2+460001.

注释[编辑]

  1. ^ 1.0 1.1 1.2 1.3 Astrometric data, mirrored by SIMBAD from the Hipparcos catalogue, pertains to the center of mass of the Capella Aa/Ab binary system. See Volume 1, The Hipparcos and Tycho Catalogues, European Space Agency, 1997, §2.3.4, and the entry in the Hipparcos catalogue (CDS ID I/239.)
  2. ^ 2.0 2.1 The cooler and more massive star, the spectroscopic primary, is the visually fainter star. See Hummel et al. 1994, §1.
  3. ^ Radial velocity figure is for the center of mass of the Capella Aa/Ab binary system. See Pourbaix 2000, Table 2.
  4. ^ 4.0 4.1 4.2 From apparent magnitude and parallax.
  5. ^ From Z=0.02 for the Sun and Hummel et al. 1994, §6.3, which gives Z=0.008 for Capella.

參考資料[编辑]

  1. ^ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 NAME CAPELLA -- Variable of RS CVn type, database entry, SIMBAD. Accessed on line December 23, 2008.
  2. ^ 2.0 2.1 Capella, Stars, Jim Kaler. Accessed on line December 23, 2008.
  3. ^ NSV 1897, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line December 23, 2008.
  4. ^ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 Very high precision orbit of Capella by long baseline interferometry, C. A. Hummel et al., The Astronomical Journal 107, #5 (May 1994), pp. 1859–1867, doi:10.1086/116995, Bibcode: 1994AJ....107.1859H. See §1 for spectral types, Table 1 for orbit, Table 5 for stellar parameters, and §6.3 for the age of the system.
  5. ^ 5.0 5.1 5.2 5.3 5.4 5.5 HR 1708, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line December 23, 2008.
  6. ^ Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses, D. Pourbaix, Astronomy and Astrophysics Supplement 145 (August 2000), pp. 215–222, doi:10.1051/aas:2000237, Bibcode: 2000A&AS..145..215P; see Table 2.
  7. ^ 7.0 7.1 On the rotation period of Capella, K. G. Strassmeier et al., Astronomische Nachrichten 322, #2 (March 2001), pp. 115–124, doi:10.1002/1521-3994(200106)322:2, Bibcode: 2001AN....322..115S.
  8. ^ 8.0 8.1 CHANDRA-LETGS X-ray observations of Capella. Temperature, density and abundance diagnostics, R. Mewe et al., Astronomy and Astrophysics 368 (March 2001), pp. 888–900, Bibcode: 2001A&A...368..888M, doi:10.1051/0004-6361:20010026; see §1.
  9. ^ Sirius Matters, Noah Brosch, Springer: 2008, ISBN 1-4020-8318-1, p. 46.
  10. ^ Entry 05167+4600, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line December 24, 2008.
  11. ^ Capella, in The Hundred Greatest Stars, James B. Kaler, Springer, 2002, ISBN 0-387-95436-8 (see §18); also doi:10.1007/0-387-21625-1_19.
  12. ^ 12.0 12.1 Capella HL, T. R. Ayres, pp. 202–204, in Cool Stars, Stellar Systems, and the Sun: Proceedings of the Third Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Held in Cambridge, Massachusetts, October 5-7, 1983, edited by Sallie L. Baliunas and Lee Hartmann, Berlin/Heidelberg, Springer-Verlag, 1984, Lecture Notes in Physics, vol. 193, ISBN 978-3-540-12907-3; doi:10.1007/3-540-12907-3_204, Bibcode: 1984LNP...193..202A
  13. ^ 畢宿星流:The Hyades stream: an evaporated cluster or an intrusion from the inner disk?, B. Famaey, F. Pont, X. Luri, S. Udry, M. Mayor, and A. Jorissen, Astronomy and Astrophysics 461, #3 (January 2007), pp. 957–962, doi:10.1051/0004-6361:20065706, Bibcode: 2007A&A...461..957F.
  14. ^ The Hyades stream: an evaporated cluster or an intrusion from the inner disk?, B. Famaey, F. Pont, X. Luri, S. Udry, M. Mayor, and A. Jorissen, Astronomy and Astrophysics 461, #3 (January 2007), pp. 957–962, doi:10.1051/0004-6361:20065706, Bibcode: 2007A&A...461..957F.
  15. ^ The spectroscopic binary Capella, W. W. Campbell, Astrophysical Journal 10 (October 1899), p. 177, doi:10.1086/140625, Bibcode: 1899ApJ....10..177C.
  16. ^ Variable velocities of stars in the line of sight, H. F. Newall, The Observatory 22 (December 1899), pp. 436–437, Bibcode: 1899Obs....22..436N.
  17. ^ Classical Observations of Visual Binary and Multiple Stars, B. Mason, pp. 88–96, in Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, Proceedings of the 240th Symposium of the International Astronomical Union, Held in Prague, Czech Republic, August 22–25, 2006, William I. Hartkopf, Edward F. Guinan, and Petr Harmanec, eds., pub. Cambridge University Press, 2006, ISBN 0-521-86348-1; doi:10.1017/S1743921307003857; see p. 94.
  18. ^ Application of Michelson's interferometer method to the measurement of close double stars, J. A. Anderson, Astrophysical Journal 51 (June 1920), pp. 263–275, doi:10.1086/142551, Bibcode: 1920ApJ....51..263A.
  19. ^ Modern Optical Interferometry, Astronomical Optical Interferometry: A Literature Review, Bob Tubbs, St. John's College, Cambridge, April 1997. Accessed on line December 30, 2008.
  20. ^ The first images from an optical aperture synthesis array: mapping of Capella with COAST at two epochs, J. E. Baldwin et al., Astronomy and Astrophysics 306 (February 1996), pp. L13–L16, Bibcode: 1996A&A...306L..13B.
  21. ^ The Brightest Stars: Discovering the Universe through the Sky's Most Brilliant Stars, Fred Schaaf, Hoboken, NJ: John Wiley & Sons, 2008, ISBN 978-0-471-70410-2; see pp. 153–155.
  22. ^ 22.0 22.1 Fisher PC, Meyerott AJ. Stellar X-Ray Emission. Ap J. 1964.1, 139 (1): 123–42. doi:10.1086/147742. 
  23. ^ 23.0 23.1 23.2 Catura RC, Acton LW, Johnson HM. Evidence for X-ray emission from Capella. Ap J. 1975.March, 196 (pt.2): L47–9. doi:10.1086/181741. 
  24. ^ Chandra/HETGS Observations of the Capella System: The Primary as a Dominating X-Ray Source, Kazunori Ishibashi et al., The Astrophysical Journal 644, #2 (June 2006), pp. L117–L120, doi:10.1086/505702, Bibcode: 2006ApJ...644L.117I.