36 Tauri


36 Tauri
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
Right ascension 04h 04m 21.67333s[1]
Declination +24° 06′ 21.5720″[1]
Apparent magnitude (V) 5.512[2]
Spectral type K0II + B7V[3]
Radial velocity (Rv)10.38 ± 0.06[4] km/s
Proper motion (μ) RA: -0.54[1] mas/yr
Dec.: -14.08[1] mas/yr
Parallax (π)2.88 ± 0.43[1] mas
Distanceapprox. 1,100 ly
(approx. 350 pc)
Absolute magnitude (MV)-1.79 (-1.40 / -0.50)[3]
Period (P)7.9412 ± 0.0093 yr
Semi-major axis (a)0.0289 ± 0.0024″
Eccentricity (e)0.683 ± 0.006
Inclination (i)149.4 ± 6.9°
Longitude of the node (Ω)260 ± 15°
Periastron epoch (T)B 1985.092 ± 0.013
Argument of periastron (ω)
287.7 ± 1.6°
Semi-amplitude (K1)
8.69 ± 0.12 km/s
Other designations
BD+23° 609, HIP 19009, HR 1252, SAO 76425
36 Tauri A: HD 25555
36 Tauri B: HD 25556
Database references

36 Tauri (abbreviated to 36 Tau) is a binary star in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of over 1,000 light years (350 parsecs) from Earth.[1] The combined apparent magnitude of the system is about 5.5,[2] meaning it can barely be seen with the naked eye, according to the Bortle scale.

36 Tauri is a spectroscopic binary. The two stars are close enough that periodic Doppler shifts in their spectra can be made out. In this case, light from both stars can be detected (and they overlap in the spectrum), so it is a double-lined system. The primary star, designated HD 25555, is a K-type bright giant, and the secondary star, designated HD 25556, is a B-type main-sequence star.[3] However, the spectrum has also been interpreted as a G-type star and an A-type main-sequence star.[5] The two stars have been resolved using speckle interferometry and are thought to have similar masses.[3]


  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. S2CID 18759600.
  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 Mason, Brian D.; McAlister, Harold A.; Hartkopf, William I.; Griffin, R. F.; Griffin, R. E. M. (1997). "Binary Star Orbits from Speckle Interferometry. X. Speckle-Spectroscopic Orbits of HR 233, 36 Tau, and 73 Leo". The Astronomical Journal. 114: 1607. Bibcode:1997AJ....114.1607M. doi:10.1086/118592.
  4. ^ Pourbaix, D.; et al. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
  5. ^ Abt, H. A. (1981). "Visual multiples. VII - MK classifications". The Astrophysical Journal Supplement Series. 45: 437. Bibcode:1981ApJS...45..437A. doi:10.1086/190719.