66 Tauri

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66 Tauri
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
Right ascension 04h 23m 51.82553s[1]
Declination +09° 27′ 39.4939″[1]
Apparent magnitude (V) 5.098[2] (5.8 / 5.9)[3]
Spectral type A3V + A4V[4]
U−B color index +0.10[5]
B−V color index +0.07[5]
Radial velocity (Rv)-8.70 ± 1[6] km/s
Proper motion (μ) RA: -20.32[1] mas/yr
Dec.: -5.32[1] mas/yr
Parallax (π)8.24 ± 0.31[1] mas
Distance400 ± 10 ly
(121 ± 5 pc)
Period (P)54.77 yr
Semi-major axis (a)0.188″
Eccentricity (e)0.720
Inclination (i)34.2°
Longitude of the node (Ω)239.8°
Periastron epoch (T)1937.24
Argument of periastron (ω)
66 Tau A
Mass2.89[7][note 1] M
Rotational velocity (v sin i)81[8] km/s
66 Tau B
Mass2.76[7][note 1] M
Other designations
r Tau, BD+09° 570, HD 27820, HIP 20522, HR 1381, SAO 111791
Database references

66 Tauri, also known as r Tauri, is a binary star in the constellation of Taurus. The combined apparent magnitude of the system is 5.098,[2] with the magnitudes of the two components being 5.8 and 5.9, respectively.[3] Parallax measurements by Hipparcos put 66 Tauri at some 400 light-years (121 parsecs) away.[1]

This is a visual binary where the positions of the two stars are tracked over time, and used to calculate an orbit. The two stars orbit each other every 55 years.[3] Their orbit is fairly eccentric, at 0.720, and the two stars are separated by 0.188″ on average.[3] Both stars are A-type main-sequence stars with similar masses.[7]


  1. ^ a b c d e f van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. 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 c d e "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 13 August 2017.
  4. ^ Christy, James W.; Walker, R. L., Jr. (1969). "MK Classification of 142 Visual Binaries". Publications of the Astronomical Society of the Pacific. 81: 643. Bibcode:1969PASP...81..643C. doi:10.1086/128831.
  5. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV data. Bibcode:1986EgUBV........0M.
  6. ^ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  7. ^ a b c Cvetkovic, Z.; Ninkovic, S. (2010). "On the Component Masses of Visual Binaries". Serbian Astronomical Journal. 180 (180): 71–80. Bibcode:2010SerAJ.180...71C. doi:10.2298/SAJ1080071C.
  8. ^ Royer, F.; Zorec, J.; Gómez, A. E. (2007). "Rotational velocities of A-type stars". Astronomy and Astrophysics. 463 (2): 671. arXiv:astro-ph/0610785. Bibcode:2007A&A...463..671R. doi:10.1051/0004-6361:20065224.


  1. ^ a b Cvetkovic et al. gives two possible mass sums: 2.89 / 2.76 M or 2.88 / 2.77 M.