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**軒轅四（天貓座α）**
	軒轅四的位置（紅圈）
觀測資料; 曆元 J2000
星座	天貓座
星官	軒轅（星宿）
赤經	09h 21m 03.30074s
赤緯	+34° 23′ 33.2245″
視星等（V）	+3.14
特性
光谱分类	K7 III
U−B 色指数	+1.95
B−V 色指数	+1.55
天体测定
徑向速度 (Rv)	37.15 km/s
自行 (μ)	赤经：–223.63 mas/yr ; 赤纬：15.18 mas/yr
视差 (π)	16.06 ± 0.17 mas
距离	203 ± 2 ly ; (62.3 ± 0.7 pc)
詳細資料
質量	~2 M☉
半徑	54.50 ± 3.02 R☉
表面重力 (log g)	1.5
亮度	673 ± 83 L☉
溫度	3,882 K
金属量 [Fe/H]	–0.26 dex
自轉速度 (v sin i)	6.4 km/s
年齡	1.4 Gyr
其他命名
	天貓座40、HR 3705、 HD 80493、BD+35 1979、HIP 45860、 SAO 61414、FK5 352、NSV 4456、GC 12880。
參考資料庫
SIMBAD	资料

軒轅四（α Lyn，α Lyncis）是在北天星座天貓座的一顆視星等+3.13的亮星^[4]。不尋常的是，它是天貓座中唯一有拜耳名字的恆星^[6]。基於視差的觀測，它與地球的距離大約是203光年（62秒差距）^[1]。

這是一顆巨星，它耗盡了核心的氫，在演化上已經離開主序帶。它已經膨脹到太陽半徑的55倍，發射的光大約是太陽光度的673倍^[7]。估計該恒星外層的有效溫度為3882K^[5]，低於太陽5778K的有效溫度，使軒轅四呈現橙色的色調，這是K型恒星的特徵^[9]。

軒轅四疑似是顆小振幅的紅色變星^[10]，它的視星等能從+3.17提升至+3.12^[11]。這種變化模式通常發生在已經形成惰性碳核並被氦-融合殼層包圍的恆星中，並表明軒轅四正開始演化為米拉型變星^[6]。

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. S2CID 18759600. arXiv:0708.1752 . doi:10.1051/0004-6361:20078357.
^ Ducati, J. R. VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system. CDS/ADC Collection of Electronic Catalogues. 2002, 2237. Bibcode:2002yCat.2237....0D.
^ Morgan, W. W.; Keenan, P. C. Spectral Classification. Annual Review of Astronomy and Astrophysics. 1973, 11: 29–50. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
^ ^4.0 ^4.1 ^4.2 Johnson, H. L.; et al. UBVRIJKL photometry of the bright stars. Communications of the Lunar and Planetary Laboratory. 1966, 4 (1): 99. Bibcode:1966CoLPL...4...99J.
^ ^5.0 ^5.1 ^5.2 ^5.3 ^5.4 ^5.5 Massarotti, A.; et al. Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity. The Astronomical Journal. 2008, 135 (1): 209–231. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209 .
^ ^6.0 ^6.1 ^6.2 ^6.3 Kaler, J. B. ALPHA LYN (Alpha Lyncis) and ALSCIAUKAT (31 Lyncis). Stars. University of Illinois. 2005-05-11 [2011-12-26]. （原始内容存档于2016-10-18）.
^ ^7.0 ^7.1 ^7.2 Piau, L.; et al. Surface convection and red giants radii measurements. Astronomy and Astrophysics. 2010, 526: 100. Bibcode:2011A&A...526A.100P. S2CID 118533297. arXiv:1010.3649 . doi:10.1051/0004-6361/201014442. For M_bol, see Table 1.
^ Alpha Lyncis. SIMBAD. 斯特拉斯堡天文資料中心. [2011-12-12].
^ The Colour of Stars. Australia Telescope Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. 2004-12-21 [2012-01-16]. （原始内容存档于2012-03-18）.
^ Percy, J. R.; et al. Photometric surveys of suspected small-amplitude red variables. III: An AAVSO photometric photometry survey. Publications of the Astronomical Society of the Pacific. 1994, 106 (700): 611–615. Bibcode:1994PASP..106..611P. doi:10.1086/133420 .
^ Kukarkin, B. V.; et al. Catalogue of suspected variable stars. Nachrichtenblatt der Vereinigung der Sternfreunde E.V. 1981. Bibcode:1981NVS...C......0K.

[aaa474_2_653-1] 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. S2CID 18759600. arXiv:0708.1752 . doi:10.1051/0004-6361:20078357.

[ducati-2] Ducati, J. R. VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system. CDS/ADC Collection of Electronic Catalogues. 2002, 2237. Bibcode:2002yCat.2237....0D.

[araa11_29-3] Morgan, W. W.; Keenan, P. C. Spectral Classification. Annual Review of Astronomy and Astrophysics. 1973, 11: 29–50. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.

[clpl4_99-4] 4.0 ^4.1 ^4.2 Johnson, H. L.; et al. UBVRIJKL photometry of the bright stars. Communications of the Lunar and Planetary Laboratory. 1966, 4 (1): 99. Bibcode:1966CoLPL...4...99J.

[aj135_1_209-5] 5.0 ^5.1 ^5.2 ^5.3 ^5.4 ^5.5 Massarotti, A.; et al. Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity. The Astronomical Journal. 2008, 135 (1): 209–231. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209 .

[kaler-6] 6.0 ^6.1 ^6.2 ^6.3 Kaler, J. B. ALPHA LYN (Alpha Lyncis) and ALSCIAUKAT (31 Lyncis). Stars. University of Illinois. 2005-05-11 [2011-12-26]. （原始内容存档于2016-10-18）.

[arXiv1010_3649-7] 7.0 ^7.1 ^7.2 Piau, L.; et al. Surface convection and red giants radii measurements. Astronomy and Astrophysics. 2010, 526: 100. Bibcode:2011A&A...526A.100P. S2CID 118533297. arXiv:1010.3649 . doi:10.1051/0004-6361/201014442. For M_bol, see Table 1.

[SIMBAD-8] Alpha Lyncis. SIMBAD. 斯特拉斯堡天文資料中心. [2011-12-12].

[csiro-9] The Colour of Stars. Australia Telescope Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. 2004-12-21 [2012-01-16]. （原始内容存档于2012-03-18）.

[asp106_700_611-10] Percy, J. R.; et al. Photometric surveys of suspected small-amplitude red variables. III: An AAVSO photometric photometry survey. Publications of the Astronomical Society of the Pacific. 1994, 106 (700): 611–615. Bibcode:1994PASP..106..611P. doi:10.1086/133420 .

[csvs-11] Kukarkin, B. V.; et al. Catalogue of suspected variable stars. Nachrichtenblatt der Vereinigung der Sternfreunde E.V. 1981. Bibcode:1981NVS...C......0K.

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