狗國增二

**狗國增二（人馬座θ²）**
	狗國增二的位置（紅圈）Location of θ2 Sagittarii (circled)
觀測資料; 曆元 J2000.0
星座	人馬座
星官
赤經	19h 59m 51.35684s
赤緯	−34° 41′ 52.0797″
視星等（V）	+5.30
特性
光谱分类	A4/A5 IV
U−B 色指数	+0.06
B−V 色指数	+0.17
天体测定
徑向速度 (Rv)	−17.60 km/s
自行 (μ)	赤经：+108.23 mas/yr ; 赤纬：−69.51 mas/yr
视差 (π)	20.62 ± 0.28 mas
距离	158 ± 2 ly ; (48.5 ± 0.7 pc)
绝对星等 (MV)	+1.87
詳細資料
質量	1.93 M☉
表面重力 (log g)	4.07±0.14
亮度	14 L☉
溫度	8,113±276 K
自轉速度 (v sin i)	45.2±0.5 km/s
年齡	809 Myr
其他命名
	θ2 Sgr、CPD−35° 8701、HD 189118、HIP 98421、HR 7624、SAO 211717、WDS J19599-3442
參考資料庫
SIMBAD	资料

狗國增二（人馬座θ²）是黃道星座人馬座中一顆單獨的恆星 ^[10]。它的視星等為 +5.30等^[2]，在足夠黑暗的場所肉眼隱約可見。這顆恆星正以每秒17.60公里的徑向速度朝向太陽接近^[4]。根據從地球測得年周視差20.62mas的數值^[1]，它與太陽的距離是158光年。

狗國增二光譜的類型是A4/A5IV^[3]，估計它的年齡為8億900萬年^[6]，是一顆演化至[A-型星|A型]]的次巨星。它被懷疑是一顆Am星，因為至少在1992年的觀測週期上，經光度測量是顆變星^[11]。估計它的質量是太陽的1.93倍^[6]，輻射是太陽的14倍^[7]，來自光球的有效溫度是8,113K^[6]。它自轉的投影自轉速度是每秒45.2公里^[8]。

狗國增二有一對目視伴星。伴星B的視星等11.3等，在2000年的角距離為32.8弧秒，位置角165°；伴星C在1965年與B的距離為1.5弧秒，位置角104度^[12]。但這兩者與狗國增二都沒有物理上的實質關係^[10]。

參考資料

^ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 van Leeuwen, F., Validation of the new Hipparcos reduction, Astronomy and Astrophysics, 2007, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752 , doi:10.1051/0004-6361:20078357.
^ ^2.0 ^2.1 ^2.2 ^2.3 Mendoza, E. E.; et al, UBVRI photometry of 225 AM stars, Astronomical Journal, June 1978, 83: 606–614, Bibcode:1978AJ.....83..606M, doi:10.1086/112242.
^ ^3.0 ^3.1 Houk, Nancy, Michigan catalogue of two-dimensional spectral types for the HD stars 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, 1979, Bibcode:1982mcts.book.....H.
^ ^4.0 ^4.1 Gontcharov, G. A., Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system, Astronomy Letters, November 2006, 32 (11): 759–771, Bibcode:2006AstL...32..759G, arXiv:1606.08053 , doi:10.1134/S1063773706110065.
^ Anderson, E.; Francis, Ch., XHIP: An extended hipparcos compilation, Astronomy Letters, 2012, 38 (5): 331, Bibcode:2012AstL...38..331A, arXiv:1108.4971 , doi:10.1134/S1063773712050015.
^ ^6.0 ^6.1 ^6.2 ^6.3 ^6.4 ^6.5 ^6.6 David, Trevor J.; Hillenbrand, Lynne A., The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets, The Astrophysical Journal, 2015, 804 (2): 146, Bibcode:2015ApJ...804..146D, arXiv:1501.03154 , doi:10.1088/0004-637X/804/2/146.
^ ^7.0 ^7.1 McDonald, I.; et al, Fundamental Parameters and Infrared Excesses of Hipparcos Stars, Monthly Notices of the Royal Astronomical Society, 2012, 427 (1): 343–57, Bibcode:2012MNRAS.427..343M, arXiv:1208.2037 , doi:10.1111/j.1365-2966.2012.21873.x.
^ ^8.0 ^8.1 Díaz, C. G.; et al, Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum, Astronomy & Astrophysics, July 2011, 531: A143, Bibcode:2011A&A...531A.143D, arXiv:1012.4858 , doi:10.1051/0004-6361/201016386.
^ tet02 Sgr. SIMBAD. 斯特拉斯堡天文資料中心. [2017-07-07].
^ ^10.0 ^10.1 Eggleton, P. P.; Tokovinin, A. A., A catalogue of multiplicity among bright stellar systems, Monthly Notices of the Royal Astronomical Society, September 2008, 389 (2): 869–879, Bibcode:2008MNRAS.389..869E, arXiv:0806.2878 , doi:10.1111/j.1365-2966.2008.13596.x.
^ Anders, G. J., Theta2 Sgr: Serendipitous Discovery of Variability in an Am Star?, Information Bulletin on Variable Stars, September 1992, 3768: 1, Bibcode:1992IBVS.3768....1A.
^ Mason, B. D.; et al, The Washington Visual Double Star Catalog, 2014 [2015-07-22], Bibcode:2001AJ....122.3466M, doi:10.1086/323920 , （原始内容存档于2019-07-04）.

[vanLeeuwen2007-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 van Leeuwen, F., Validation of the new Hipparcos reduction, Astronomy and Astrophysics, 2007, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752 , doi:10.1051/0004-6361:20078357.

[Mendoza1978-2] 2.0 ^2.1 ^2.2 ^2.3 Mendoza, E. E.; et al, UBVRI photometry of 225 AM stars, Astronomical Journal, June 1978, 83: 606–614, Bibcode:1978AJ.....83..606M, doi:10.1086/112242.

[houk1979-3] 3.0 ^3.1 Houk, Nancy, Michigan catalogue of two-dimensional spectral types for the HD stars 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, 1979, Bibcode:1982mcts.book.....H.

[Gontcharov2006-4] 4.0 ^4.1 Gontcharov, G. A., Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system, Astronomy Letters, November 2006, 32 (11): 759–771, Bibcode:2006AstL...32..759G, arXiv:1606.08053 , doi:10.1134/S1063773706110065.

[Anderson2012-5] Anderson, E.; Francis, Ch., XHIP: An extended hipparcos compilation, Astronomy Letters, 2012, 38 (5): 331, Bibcode:2012AstL...38..331A, arXiv:1108.4971 , doi:10.1134/S1063773712050015.

[David2015-6] 6.0 ^6.1 ^6.2 ^6.3 ^6.4 ^6.5 ^6.6 David, Trevor J.; Hillenbrand, Lynne A., The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets, The Astrophysical Journal, 2015, 804 (2): 146, Bibcode:2015ApJ...804..146D, arXiv:1501.03154 , doi:10.1088/0004-637X/804/2/146.

[Mcdonald2012-7] 7.0 ^7.1 McDonald, I.; et al, Fundamental Parameters and Infrared Excesses of Hipparcos Stars, Monthly Notices of the Royal Astronomical Society, 2012, 427 (1): 343–57, Bibcode:2012MNRAS.427..343M, arXiv:1208.2037 , doi:10.1111/j.1365-2966.2012.21873.x.

[Diaz2011-8] 8.0 ^8.1 Díaz, C. G.; et al, Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum, Astronomy & Astrophysics, July 2011, 531: A143, Bibcode:2011A&A...531A.143D, arXiv:1012.4858 , doi:10.1051/0004-6361/201016386.

[SIMBAD-9] tet02 Sgr. SIMBAD. 斯特拉斯堡天文資料中心. [2017-07-07].

[Eggleton2008-10] 10.0 ^10.1 Eggleton, P. P.; Tokovinin, A. A., A catalogue of multiplicity among bright stellar systems, Monthly Notices of the Royal Astronomical Society, September 2008, 389 (2): 869–879, Bibcode:2008MNRAS.389..869E, arXiv:0806.2878 , doi:10.1111/j.1365-2966.2008.13596.x.

[Anders1992-11] Anders, G. J., Theta2 Sgr: Serendipitous Discovery of Variability in an Am Star?, Information Bulletin on Variable Stars, September 1992, 3768: 1, Bibcode:1992IBVS.3768....1A.

[WDSC2014-12] Mason, B. D.; et al, The Washington Visual Double Star Catalog, 2014 [2015-07-22], Bibcode:2001AJ....122.3466M, doi:10.1086/323920 , （原始内容存档于2019-07-04）.

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狗國增二

參考資料

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