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天弁二盾牌座δ)是在南天盾牌座的一顆巨星視星等4.72等[4],是在這個小且沒有特徵星座的第五亮星。分析依巴谷衛星任務期間測量的視差,這顆恆星與地球的距離大約是202光年(62秒差距[1]。天弁二是盾牌座δ變星的原型,這種變星來自體積脹縮造成光度的高振幅大約都在0.15星等左右。這顆恆星特有的化學豐度與Am星相似[8]

天弁二(盾牌座δ)
Scutum constellation map.png

天弁二的位置(中心)。
觀測資料
曆元 J2000
星座 盾牌座
星官
赤經 18h 42m 16.422137s[1]
赤緯 −09° 03′ 09.19206″[1]
視星等(V) 4.60 - 4.79[2]
特性
光谱分类F2 IIIp[3]
U−B 色指数+0.16[4][2]
B−V 色指数+0.35[4]
变星类型盾牌座δ
天体测定
徑向速度 (Rv)−44.8[5] km/s
自行 (μ) 赤经:9.21[1] mas/yr
赤纬:0.82[1] mas/yr
视差 (π)16.11 ± 0.31[1] mas
距离202 ± 4 ly
(62 ± 1 pc)
绝对星等 (MV)0.72±0.04[6]
詳細資料
質量2.23+0.06
−0.05
[7] M
表面重力 (log g)3.5[8]
溫度7000[8] K
金属量 [Fe/H]0.41[6] dex
自轉速度 (v sin i)25.5[8] km/s
年齡0.7±0.1[6] Gyr
其他命名
盾牌座2、BD−09° 4796, FK5 1486、HD 172748、HIP 91726、HR 7020、 SAO 142515。[9]
參考資料庫
SIMBADdata

在1900年,天文學家威廉·華萊士·坎貝爾(William Wallace Campbell)和威廉·哈蒙德·賴特英语William Hammond Wright使用利克天文台的米爾斯光譜儀確定該恆星的徑向速度會變化[10]。在1935年,測量出光度以0.19377日(4.65小時)的週期有著0.2等(在+4.60至+4.79之間變化)的振幅,並證實這種變化是內在的,而不是光譜聯星造成的結果[11]。在1938年,發現了次要的週期,並提出脈動理論來模擬這種變異[12]。之後對天弁二的觀測表明,它是在多重離散的徑向和非徑向模式下脈動。模式最強的頻率是59.731μHz,其次是61.936μHz,依此類推,現在共建模了八種不同的頻率模式[13]

這顆恆星在銀道坐標系空間速度[U, V, W] = [–42, –17, –1] km·s−1。它以離心率0.11的軌道繞行銀河系,最接近銀河中心的距離是22.31 kly(6.84 kpc),最遠的距離是27.59 kly(8.46 kpc)[6]。如果天弁二維持現在的運動和光度,它將以10光年的距離內經過太陽系附近[14],並且在西元11500001330000 CE成為天空中最亮的恆星,視星等為-1.84,比天狼星現在的-1.46還要明亮[15]

天弁二有二顆光學伴星。第一顆距離15.2角秒,視星等+12.2。第二顆距離53角秒,視星等+9.2[16]

佛蘭斯蒂德沒有將天弁二標示在盾牌座,而是將它與其它幾顆星納入天鷹座,並在星表中標記為天鷹座2拜耳名稱的盾牌座δ是由古德命名的[17]

參考資料编辑

  1. ^ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F., Validation of the new Hipparcos reduction, Astronomy and Astrophysics, November 2007, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752, doi:10.1051/0004-6361:20078357 
  2. ^ 2.0 2.1 Samus, N. N.; Durlevich, O. V.; 等. 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. 
  3. ^ Cowley, Anne; Fraquelli, Dorothy, MK Spectral Types for Some Bright F Stars, Publications of the Astronomical Society of the Pacific, February 1974, 86 (509): 7, Bibcode:1974PASP...86...70C, doi:10.1086/129562 
  4. ^ 4.0 4.1 4.2 Johnson, H. L.; 等. UBVRIJKL photometry of the bright stars. Communications of the Lunar and Planetary Laboratory. 1966, 4 (99): 99. Bibcode:1966CoLPL...4...99J. 
  5. ^ Evans, D. S. The Revision of the General Catalogue of Radial Velocities. (编) Batten, Alan Henry; Heard, John Frederick. Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. June 20–24, 1966. Bibcode:1967IAUS...30...57E. 
  6. ^ 6.0 6.1 6.2 6.3 Holmberg, J.; Nordström, B.; Andersen, J., The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics, Astronomy and Astrophysics, July 2009, 501 (3): 941–947, Bibcode:2009A&A...501..941H, arXiv:0811.3982, doi:10.1051/0004-6361/200811191 
  7. ^ Nordström, B.; 等, The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs, Astronomy and Astrophysics, May 2004, 418: 989–1019, Bibcode:2004A&A...418..989N, arXiv:astro-ph/0405198, doi:10.1051/0004-6361:20035959 
  8. ^ 8.0 8.1 8.2 8.3 Yushchenko, A.; 等. The chemical composition of δ Scuti. Monthly Notices of the Royal Astronomical Society. May 2005, 359 (55): 865–873. Bibcode:2005MNRAS.359..865Y. doi:10.1111/j.1365-2966.2005.08921.x. 
  9. ^ del Sct – Variable star of delta Sct type. SIMBAD Astronomical Object Database. Centre de Données astronomiques de Strasbourg. [2009-10-23]. 
  10. ^ Campbell, W. W.; Wright, W. H. A list of nine stars whose velocities in the line of sight are variable. Astrophysical Journal. 1900, 12: 254–257. Bibcode:1900ApJ....12..254C. doi:10.1086/140765.  Listed as 2 Scuti on p. 256.
  11. ^ Colacevich, A. On the variable radial velocity of δ Scuti. Publications of the Astronomical Society of the Pacific. August 1935, 47 (278): 231–232. Bibcode:1935PASP...47..231C. doi:10.1086/124599. 
  12. ^ Sterne, T. E. The Secondary Variation of δ Scuti. Astrophysical Journal. March 1938, 87: 133–150. Bibcode:1938ApJ....87..133S. doi:10.1086/143913. 
  13. ^ Templeton, Matthew R.; 等. A New Pulsation Spectrum and Asteroseismology of delta Scuti. The Astronomical Journal. October 1997, 114: 1592–1601. Bibcode:1997AJ....114.1592T. doi:10.1086/118590. 
  14. ^ García-Sánchez, J.; 等, Stellar encounters with the solar system, Astronomy and Astrophysics, 2001, 379 (2): 634–659, Bibcode:2001A&A...379..634G, doi:10.1051/0004-6361:20011330 
  15. ^ Sky and Telescope, April 1998 (p60), based on computations from Hipparcos mission data.
  16. ^ Burnham, Robert. Burnham's celestial handbook: an observer's guide to the universe beyond the solar system 3. Courier Dover Publications. 1978: 1746. ISBN 0-486-23673-0. 
  17. ^ Wagman, M. Flamsteed's Missing Stars. Journal for the History of Astronomy, Vol.18, NO. 3/AUG, P.209, 1987. August 1987, 18: 212. Bibcode:1987JHA....18..209W. doi:10.1177/002182868701800305. 

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