Delta1 Tauri

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Delta1 Tauri
Taurus IAU.svg
link=δ2 Tau

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[1] mas
Distance 156 ± 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
Mass 2.8±0.5 M
Radius 11.4 R
Luminosity 69 L
Temperature 5,000 K
Metallicity [Fe/H] +0.10 dex
Rotation 138.2 d
Rotational velocity (v sin i) 4.2 km/s
Age 620[8] Myr
δ1 Tau Ab
Mass 1.28±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

Delta1 Tauri (δ1 Tauri) is an orange-hued binary star[10] system in the zodiac constellation of Taurus. It has the traditional name Hyadum II, which is Latin for "Second Hyad". No other traditional names are associated to it.[11] 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]

This is a single-lined spectroscopic binary star system 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 has 2.8 times the mass of the Sun, while the secondary, component Ab, has 1.3 times the Sun's mass.[7]

There is a magnitude 13.21 visual companion, component B, separated by 111.8 arcseconds from the main star.[3] It is most likely not physically related to the main star.[10]


  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:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  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: 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/0409683Freely accessible, Bibcode:2005A&A...430..303C, doi:10.1051/0004-6361:20041440. 
  6. ^ a b Pourbaix, D.; et al. (2004), "SB9: The Ninth Catalogue of Spectroscopic Binary Orbits", Astronomy & Astrophysics, 424: 727–732, Bibcode:2009yCat....102020P, doi:10.1051/0004-6361:20041213. 
  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:1407.6352Freely accessible, Bibcode:2015A&A...573A.138B, doi:10.1051/0004-6361/201323019, 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:1410.6422Freely accessible, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474. 
  9. ^ "del01 Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-08. 
  10. ^ a b 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:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  11. ^ Kaler, James B., "Hyadum II", STARS, University of Illinois, retrieved 2017-08-09.