Delta Boötis

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δ Boötis
Diagram showing star positions and boundaries of the Boötes constellation and its surroundings
Cercle rouge 100%.svg

Location of δ Boötis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
BD+33 2561
Right ascension 15h 15m 30.16295s[1]
Declination +33° 18′ 53.3926″[1]
Apparent magnitude (V) 3.482[2]
BD+33 2562
Right ascension 15h 15m 38.34906s[1]
Declination +33° 19′ 15.3161″[1]
Apparent magnitude (V) 7.81[3]
Spectral type G8 III[4] + G0 V[3]
U−B color index +0.656[2]/+0.02[3]
B−V color index +0.951[2]/+0.59[3]
BD+33 2561
Radial velocity (Rv) –12.3[5] km/s
Proper motion (μ) RA: +84.74[1] mas/yr
Dec.: –111.58[1] mas/yr
Parallax (π) 26.78 ± 0.16[1] mas
Distance 121.8 ± 0.7 ly
(37.3 ± 0.2 pc)
Absolute magnitude (MV) +0.700[6]
BD+33 2562
Radial velocity (Rv) –12.1[5] km/s
Proper motion (μ) RA: +83.48[1] mas/yr
Dec.: –110.41[1] mas/yr
Parallax (π) 27.05 ± 0.73[1] mas
Distance 121 ± 3 ly
(37.0 ± 1.0 pc)
BD+33 2561
Radius 10.5 ± 0.2[7] R
Luminosity 53.7[6] L
Surface gravity (log g) 2.56[8] cgs
Temperature 4,847[8] K
Metallicity [Fe/H] –0.44[8] dex
Rotational velocity (v sin i) 3.6[9] km/s
Other designations
49 Boötis, ADS 9559 A/B, HR 5681, HD 135722, BD+33 2561/2562, FK5 563, HIP 74666/74674, SAO 64589/64591.[10]
Database references
Database references

Delta Boötis (δ Boo, δ Boötis) is a double star in the northern constellation Boötes. Based upon parallax measurements, it is located at a distance of approximately 121.8 light-years (37.3 parsecs) from the Earth.[1] This star is sometimes called Princeps, meaning prince or prime in Latin. The origin of this name is unclear, although it usually appears in an astrological context.[11][12] The It has an apparent visual magnitude of this star is 3.5,[2] making it visible to the naked eye even during a Full Moon.

In Chinese, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of δ Boötis, 42 Herculis, τ Herculis, φ Herculis, χ Herculis, ν1 Boötis and μ1 Boötis.[13] Consequently, δ Boötis itself is known as 七公七 (Qī Gōng qī, English: the Seventh Star of Seven Excellencies.)[14]


This system consists of a pair of stars located in physical proximity to each other and sharing a similar motion through space, suggesting that they may form a binary star system. Based upon their angular separation and their distance, they have a projected separation of 3,800 Astronomical Units (AU). However, their separation along the line of sight from the Earth remains uncertain, so all that can really be said is that they are separated by at least 3,800 AU. If they are gravitationally bound to each other, it requires a minimum of 120,000 years to complete an orbit.[15]

The brighter member of the pair has a stellar classification of G8 III,[4] indicating that it has exhausted the supply of hydrogen at its core and evolved into a giant star. It now has a radius more than ten times the radius of the Sun.[7] Compared to the Sun, this star appears deficient in elements other than hydrogen and helium—what astronomers term the star's metallicity. The outer envelope of this star has an effective temperature of 4,847 K,[8] which is what gives it the characteristic yellow hue of a G-type star.[16]

The secondary component has a stellar classification of G0 V,[3] which suggests it is a main sequence star that may be similar in physical properties to the Sun. The apparent visual magnitude of this star is 7.81,[3] making it much less luminous than the primary component.[17]


  1. ^ a b c d e f g h i j k van Leeuwen, F. (November 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 c d e f Tolbert, Charles Ray (May 1964), "A UBV Study of 94 Wide Visual Binaries", Astrophysical Journal, 139: 1105, Bibcode:1964ApJ...139.1105T, doi:10.1086/147852 
  4. ^ a b Tsvetkov, A. S.; Popov, A. V.; Smirnov, A. A. (January 2008), "Inaccuracies in the spectral classification of stars from the Tycho-2 Spectral Type Catalogue", Astronomy Letters, 34 (1): 17–27, Bibcode:2008AstL...34...17T, doi:10.1134/S1063773708010039 
  5. ^ a b Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E, retrieved 2009-09-10 
  6. ^ a b Böhm-Vitense, Erika; et al. (December 2000), "Ultraviolet Emission Lines in BA and Non-BA Giants", The Astrophysical Journal, 545 (2): 992−999, Bibcode:2000ApJ...545..992B, doi:10.1086/317850. 
  7. ^ a b Nordgren, Tyler E.; et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal, 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114 
  8. ^ a b c d Frasca, A.; et al. (December 2009), "REM near-IR and optical photometric monitoring of pre-main sequence stars in Orion. Rotation periods and starspot parameters", Astronomy and Astrophysics, 508 (3): 1313–1330, Bibcode:2009A&A...508.1313F, doi:10.1051/0004-6361/200913327 
  9. ^ Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209 
  10. ^ "del Boo -- Star in double system", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-05 
  11. ^ Robson, Vivian E. (2005), The Fixed Stars and Constellations in Astrology, Astrology Center of America, p. 112, ISBN 1-933303-13-1 
  12. ^ Constellations of Word - Boötes (Princeps)
  13. ^ (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.
  14. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日
  15. ^ Kaler, James B., "DELTA BOO (Delta Bootis)", Stars, University of Illinois, retrieved 2012-01-05 
  16. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16 
  17. ^ The actual brightness ratio is given by 2.512Δm, where Δm is the difference in magnitude. For this pair, Δm = –4.33, so the ratio is 2.512−4.33 = 0.019. Hence the secondary component is 1.9% as bright as the primary.

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