天弁二

**天弁二（盾牌座δ）**
	; 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
SIMBAD	资料

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]。

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6999193770000000000♠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的空間速度是[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7006115000000000000♠1150000至7006133000000000000♠1330000 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

van Leeuwen, F., , Astronomy and Astrophysics, November 2007, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752 , doi:10.1051/0004-6361:20078357
Samus, N. N.; Durlevich, O. V.; et al. . VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 2009, 1. Bibcode:2009yCat....102025S.
Cowley, Anne; Fraquelli, Dorothy, , Publications of the Astronomical Society of the Pacific, February 1974, 86 (509): 7, Bibcode:1974PASP...86...70C, doi:10.1086/129562
Johnson, H. L.; et al. . Communications of the Lunar and Planetary Laboratory. 1966, 4 (99): 99. Bibcode:1966CoLPL...4...99J.
Evans, D. S. . Batten, Alan Henry; Heard, John Frederick (编). . University of Toronto: International Astronomical Union. June 20–24, 1966. Bibcode:1967IAUS...30...57E.
Holmberg, J.; Nordström, B.; Andersen, J., , Astronomy and Astrophysics, July 2009, 501 (3): 941–947, Bibcode:2009A&A...501..941H, arXiv:0811.3982 , doi:10.1051/0004-6361/200811191
Nordström, B.; et al, , Astronomy and Astrophysics, May 2004, 418: 989–1019, Bibcode:2004A&A...418..989N, arXiv:astro-ph/0405198 , doi:10.1051/0004-6361:20035959
Yushchenko, A.; et al. . 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.
. SIMBAD Astronomical Object Database. Centre de Données astronomiques de Strasbourg. [2009-10-23]. （原始内容存档于2020-11-05）.
Campbell, W. W.; Wright, W. H. . Astrophysical Journal. 1900, 12: 254–257. Bibcode:1900ApJ....12..254C. doi:10.1086/140765. Listed as 2 Scuti on p. 256.
Colacevich, A. . Publications of the Astronomical Society of the Pacific. August 1935, 47 (278): 231–232. Bibcode:1935PASP...47..231C. doi:10.1086/124599.
Sterne, T. E. . Astrophysical Journal. March 1938, 87: 133–150. Bibcode:1938ApJ....87..133S. doi:10.1086/143913.
Templeton, Matthew R.; et al. . The Astronomical Journal. October 1997, 114: 1592–1601. Bibcode:1997AJ....114.1592T. doi:10.1086/118590.
García-Sánchez, J.; et al, , Astronomy and Astrophysics, 2001, 379 (2): 634–659, Bibcode:2001A&A...379..634G, doi:10.1051/0004-6361:20011330
Sky and Telescope, April 1998 (p60), based on computations from Hipparcos mission data.
Burnham, Robert. 3. Courier Dover Publications. 1978: 1746. ISBN 0-486-23673-0.
Wagman, M. . 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.

外部連結

AAVSO Variable Star of the Month: Delta Scuti and the Delta Scuti Variables （页面存档备份，存于）

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[aaa474_2_653-1] van Leeuwen, F., , Astronomy and Astrophysics, November 2007, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752 , doi:10.1051/0004-6361:20078357

[gcvs-2] Samus, N. N.; Durlevich, O. V.; et al. . VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 2009, 1. Bibcode:2009yCat....102025S.

[pasp86_509_7-3] Cowley, Anne; Fraquelli, Dorothy, , Publications of the Astronomical Society of the Pacific, February 1974, 86 (509): 7, Bibcode:1974PASP...86...70C, doi:10.1086/129562

[clpl99-4] Johnson, H. L.; et al. . Communications of the Lunar and Planetary Laboratory. 1966, 4 (99): 99. Bibcode:1966CoLPL...4...99J.

[rgcrv-5] Evans, D. S. . Batten, Alan Henry; Heard, John Frederick (编). . University of Toronto: International Astronomical Union. June 20–24, 1966. Bibcode:1967IAUS...30...57E.

[aaa501_3_941-6] Holmberg, J.; Nordström, B.; Andersen, J., , Astronomy and Astrophysics, July 2009, 501 (3): 941–947, Bibcode:2009A&A...501..941H, arXiv:0811.3982 , doi:10.1051/0004-6361/200811191

[aaa418_989-7] Nordström, B.; et al, , Astronomy and Astrophysics, May 2004, 418: 989–1019, Bibcode:2004A&A...418..989N, arXiv:astro-ph/0405198 , doi:10.1051/0004-6361:20035959

[mnras359-8] Yushchenko, A.; et al. . 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.

[SIMBAD-9] . SIMBAD Astronomical Object Database. Centre de Données astronomiques de Strasbourg. [2009-10-23]. （原始内容存档于2020-11-05）.

[apj12_254-10] Campbell, W. W.; Wright, W. H. . Astrophysical Journal. 1900, 12: 254–257. Bibcode:1900ApJ....12..254C. doi:10.1086/140765. Listed as 2 Scuti on p. 256.

[pasp47_278_231-11] Colacevich, A. . Publications of the Astronomical Society of the Pacific. August 1935, 47 (278): 231–232. Bibcode:1935PASP...47..231C. doi:10.1086/124599.

[apj87_133-12] Sterne, T. E. . Astrophysical Journal. March 1938, 87: 133–150. Bibcode:1938ApJ....87..133S. doi:10.1086/143913.

[apj114-13] Templeton, Matthew R.; et al. . The Astronomical Journal. October 1997, 114: 1592–1601. Bibcode:1997AJ....114.1592T. doi:10.1086/118590.

[aaa379_2_634-14] García-Sánchez, J.; et al, , 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.

[burnham1978-16] Burnham, Robert. 3. Courier Dover Publications. 1978: 1746. ISBN 0-486-23673-0.

[17] Wagman, M. . 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.