Chi Tauri

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Chi Tauri
Diagram showing star positions and boundaries of the Taurus constellation and its surroundings
Cercle rouge 100%.svg

Location of χ Tauri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
χ Tau A
Right ascension 04h 22m 34.94293s[1]
Declination +25° 37′ 45.5379″[1]
Apparent magnitude (V) 5.378[2]
χ Tau B
Right ascension 04h 22m 35.532s[3]
Declination +25° 38′ 03.35″[3]
Apparent magnitude (V) 8.40[4]
χ Tau A
Spectral type B9V[5]
U−B color index -0.12[6]
B−V color index -0.04[6]
χ Tau B
Spectral type F8 + G6 + K4 + K4[5]
U−B color index +0.10[6]
B−V color index +0.63[6]
χ Tau A
Radial velocity (Rv) +15.3 ± 3.4[5] km/s
Proper motion (μ) RA: 19.42[1] mas/yr
Dec.: -17.16[1] mas/yr
Parallax (π) 11.20 ± 0.27[1] mas
Distance 291 ± 7 ly
(89 ± 2 pc)
Absolute magnitude (MV) 0.82 ± 0.18[5]
χ Tau B
Radial velocity (Rv) +14.694 ± 0.081[5] km/s
Proper motion (μ) RA: 17.21[7] mas/yr
Dec.: -13.16[7] mas/yr
Absolute magnitude (MV) 3.85 ± 0.18 (total)
4.20 ± 0.18 (Ba)
5.27 ± 0.18 (Bb)
7.87 / 7.87 (Bc)[5]
Primary χ Tau Ba
Companion χ Tau Bb
Period (P) 17.602309 ± 0.000036 d
Eccentricity (e) 0.2938 ± 0.0013
Inclination (i) 53.3 ± 0.5°
Periastron epoch (T) 2448891.649 ± 0.014
Argument of periastron (ω)
249.43 ± 0.33°
Semi-amplitude (K1)
41.287 ± 0.080 km/s
Semi-amplitude (K2)
48.133 ± 0.080 km/s
Primary χ Tau Bab
Companion χ Tau Bc
Period (P) 3450.6 ± 6.1 d
Eccentricity (e) 0.3560 ± 0.0068
Inclination (i) 73 ± 6°
Periastron epoch (T) 2447546.5 ± 9.7
Argument of periastron (ω)
250.3 ± 1.5°
Semi-amplitude (K1)
8.625 ± 0.067 km/s
Age 200 ± 50[5] Myr
χ Tau A
Mass 2.60 ± 0.05[5] M
Radius 2.15[8] R
Surface gravity (log g) 4.15 ± 0.14[9] cgs
Temperature 10300 ± 300[5] K
Rotational velocity (v sin i) 263[9] km/s
χ Tau Ba
Mass 1.19[5] M
Surface gravity (log g) 4.5[5] cgs
Temperature 6180 ± 150[5] K
Rotational velocity (v sin i) 1 ± 3[5] km/s
χ Tau Bb
Mass 1.02[5] M
Surface gravity (log g) 4.5[5] cgs
Temperature 5620 ± 150[5] K
Rotational velocity (v sin i) 1 ± 3[5] km/s
χ Tau Bc
Mass ~0.70 / 0.70[5] M
Other designations
χ Tau, 59 Tau, BD+25° 707, HD 27638, HIP 20430, HR 1369, SAO 76573, ADS 3161 AB, CCDM J04226+2538AB
Database references
χ Tau B

Chi Tauri (χ Tau, χ Tau) is a star system in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 291 light years (89 parsecs) from Earth. The primary component has an apparent magnitude of about 5.4,[2] meaning it is visible with the naked eye.

The main component of the system is Chi Tauri A. It is a B-type main-sequence star. Its mass is 2.6 times that of the Sun and its surface glows with an effective temperature of 10,300 K. It may be a binary star itself, as suggested from astrometric data from Hipparcos, although no orbit could be derived.[5]

The secondary component of the system is Chi Tauri B, separated about 19″[5] from Chi Tauri A. It was thought to be a post-T Tauri star from its unusual spectrum,[10] but later studies ruled this out.[5] It is a double-lined spectroscopic binary—the two stars are not resolved but their spectra have periodic Doppler shifts indicating orbital motion. The two stars are an F-type star and a G-type star, respectively, and are designated Ba and Bb.[5]

The radial velocity of Chi Tauri B has a slow drift indicating the presence of another star in the system. Designated Chi Tauri Bc, this massive object is too dim to be detected, but it appears in Chi Tauri B's spectrum as an infrared excess. Because of this infrared excess, this unseen component is thought to be a pair of K-type main-sequence stars both with masses 70% of the Sun. The stars within the system appear to be dynamically interacting.[5]


  1. ^ a b c d e van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. 
  3. ^ a b Zacharias, N. (2012). "The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)". VizieR On-line Data Catalog. 1322. Bibcode:2012yCat.1322....0Z. 
  4. ^ "* chi Tau B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 8 May 2017. 
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y Torres, Guillermo (2006). "The Multiple System HD 27638". The Astronomical Journal. 131 (3): 1702. arXiv:astro-ph/0512254Freely accessible. Bibcode:2006AJ....131.1702T. doi:10.1086/500355. 
  6. ^ a b c d Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. Bibcode:1986EgUBV........0M. 
  7. ^ a b Röser, S.; Schilbach, E.; Schwan, H.; Kharchenko, N. V.; Piskunov, A. E.; Scholz, R.-D. (2008). "PPM-Extended (PPMX) – a catalogue of positions and proper motions". Astronomy and Astrophysics. 488: 401. arXiv:0806.1009Freely accessible. Bibcode:2008A&A...488..401R. doi:10.1051/0004-6361:200809775. 
  8. ^ Pasinetti Fracassini, L. E.; et al. (2001). "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics". Astronomy & Astrophysics. 367 (2): 521–24. arXiv:astro-ph/0012289Freely accessible. Bibcode:2001A&A...367..521P. doi:10.1051/0004-6361:20000451. 
  9. ^ a b David, Trevor J.; Hillenbrand, Lynne A. (2015). "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. 804 (2): 146. arXiv:1501.03154Freely accessible. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. 
  10. ^ Lindroos, K. P. (1986). "A study of visual double stars with early-type primaries. V - Post-T Tauri secondaries". Astronomy and Astrophysics. 156 (1–2): 223–233. Bibcode:1986A&A...156..223L.