Delta1 Tauri


Delta¹ Tauri (δ¹ Tauri, abbreviated Delta¹ Tau, δ¹ Tau) is a double star in the zodiac constellation of Taurus. Based upon an annual parallax shift of 20.96 mas as seen from Earth,[1] it is located roughly 156 light-years distant from the Sun. The system is faintly visible to the naked eye with a combined apparent visual magnitude of +3.772.[2] It is considered a member of the Hyades cluster.[7]

Delta¹ Tauri
Taurus IAU.svg
Red circle.svg
Location of δ¹ Tauri (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Taurus
Right ascension 04h 22m 56.09253s[1]
Declination +17° 32′ 33.0487″[1]
Apparent magnitude (V) +3.772[2] (3.90 + 9.50)[3]
Spectral type G9.5 III CN0.5[4]
U−B color index +0.801[2]
B−V color index +0.919[2]
Proper motion (μ) RA: +106.56[1] mas/yr
Dec.: −29.18[1] mas/yr
Parallax (π)20.96 ± 0.58 mas[1]
Distance156 ± 4 ly
(48 ± 1 pc)
Absolute magnitude (MV)+0.41[5]
Period (P)529.8 d
Eccentricity (e)0.42
Periastron epoch (T)2434356.5 JD
Argument of periastron (ω)
Semi-amplitude (K1)
3.0 km/s
δ¹ Tau Aa
Mass2.8±0.5 M
Radius11.4 R
Luminosity69 L
Temperature5,000 K
Metallicity [Fe/H]+0.10 dex
Rotation138.2 d
Rotational velocity (v sin i)4.2 km/s
Age620[8] Myr
δ¹ Tau Ab
Mass1.28±0.1 M
Other designations
Hyadum II, δ¹ Tau, 61 Tauri, BD+17°712, FK5 162, HD 27697, HIP 20455, HR 1373, SAO 93897[9]
Database references

The two constituents are designated δ¹ Tauri A and B. A is itself a binary star with components designated δ¹ Tauri Aa (officially named Secunda Hyadum /sɪˈkʌndə ˈhədəm/, the traditional name for the entire system)[10] and Ab.


δ¹ Tauri (Latinised to Delta¹ Tauri) is the system's Bayer designation. The designations of the two constituents as Delta¹ Tauri A and B, and those of A's components - Delta¹ Tauri Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[11]

The system bore the traditional name Hyadum II, which is Latin for "Second of the Hyades".[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[14] It approved the name Secunda Hyadum for the component Delta¹ Tauri Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[10]

In Chinese, 畢宿 (Bì Xiù), meaning Net, refers to an asterism consisting of δ¹ Tauri, Epsilon Tauri, Delta³ Tauri, Gamma Tauri, Alpha Tauri (Aldebaran), 71 Tauri and Lambda Tauri.[15] Consequently, the Chinese name for Delta¹ Tauri itself is 畢宿三 (Bì Xiù sān), "the Third Star of Net".[16]


Delta¹ Tauri A is a single-lined spectroscopic binary with an orbital period of 529.8 days and an eccentricity of 0.42.[6] The visible member, component Aa, is an evolved G- or K-type giant star with a stellar classification of G9.5 III CN0.5.[4] The 'CN0.5' suffix indicates a mild overabundance of cyanogen in the outer atmosphere. It is chromospherically active and shows a radial velocity variation of 9.3±0.2 m/s with a period of 165±3 d.[7] The primary, component Aa, has 2.8 times the mass of the Sun, while the secondary, component Ab, has 1.3 times the Sun's mass.[7]

Delta¹ Tauri B is a magnitude 13.21 visual companion separated by 111.8 arcseconds from A.[3] It is most likely not physically related to the main star.[17]


  1. ^ a b c d e f van Leeuwen, F. (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 c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants", Monthly Notices of the Royal Astronomical Society, 172 (3): 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667.
  3. ^ a b Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122: 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  4. ^ a b Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  5. ^ Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars", Astronomy and Astrophysics, 430: 303–311, arXiv:astro-ph/0409683, Bibcode:2005A&A...430..303C, doi:10.1051/0004-6361:20041440, S2CID 12136256.
  6. ^ a b Pourbaix, D.; et al. (2004), "SB9: The Ninth Catalogue of Spectroscopic Binary Orbits", Astronomy & Astrophysics, 424: 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
  7. ^ a b c d Beck, P. G.; et al. (January 2015), "Detection of solar-like oscillations in the bright red giant stars γ Psc and θ1 Tau from a 190-day high-precision spectroscopic multisite campaign", Astronomy & Astrophysics, 573: 15, arXiv:1407.6352, Bibcode:2015A&A...573A.138B, doi:10.1051/0004-6361/201323019, S2CID 33898282, A138.
  8. ^ Jofré, E.; et al. (2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574: A50, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, S2CID 53666931.
  9. ^ "del01 Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-08.{{cite web}}: CS1 maint: postscript (link)
  10. ^ a b "Naming Stars". Retrieved 16 December 2017.
  11. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  12. ^ Kaler, James B., "Hyadum II", STARS, University of Illinois, retrieved 2017-08-09.
  13. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  14. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  15. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  16. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.