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δ Boötis
	Location of δ Boötis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Boötes
	BD+33 2561
Right ascension	15h 15m 30.16282s
Declination	+33° 18′ 53.3925″
Apparent magnitude (V)	3.482
	BD+33 2562
Right ascension	15h 15m 38.34898s
Declination	+33° 19′ 15.3187″
Apparent magnitude (V)	7.81
Characteristics
BD+33 2561
Spectral type	G8 III
U−B color index	+0.656/
B−V color index	+0.951/
BD+33 2562
Spectral type	G0 V
U−B color index	+0.02
B−V color index	+0.59
Astrometry
BD+33 2561
Radial velocity (Rv)	−12.29±0.16 km/s
Proper motion (μ)	RA: +84.383 mas/yr ; Dec.: −111.591 mas/yr
Parallax (π)	27.0746 ± 0.1256 mas
Distance	120.5 ± 0.6 ly ; (36.9 ± 0.2 pc)
Absolute magnitude (MV)	+0.700
BD+33 2562
Radial velocity (Rv)	−11.83±0.18 km/s
Proper motion (μ)	RA: +82.776 mas/yr ; Dec.: –110.040 mas/yr
Parallax (π)	27.0648 ± 0.0307 mas
Distance	120.5 ± 0.1 ly ; (36.95 ± 0.04 pc)
Details
BD+33 2561
Mass	1.5 M☉
Radius	11.43±0.07 R☉
Luminosity	58.1 L☉
Surface gravity (log g)	2.38±0.09 cgs
Temperature	4,810±30 K
Metallicity [Fe/H]	−0.35±0.03 dex
Rotational velocity (v sin i)	3.6 km/s
BD+33 2562
Mass	0.98 M☉
Radius	0.91±0.02 R☉
Luminosity	0.87 L☉
Temperature	5,812±67 K
Age	3.09 Gyr
Other designations
	STF 4027, ADS 9559, WDS 15155+3319
	A: δ Boo, 49 Boötis, BD+33 2561, FK5 563, HD 135722, HIP 74666, HR 5681, SAO 64589
	B: BD+33 2562, HIP 74674, SAO 64591
Database references
SIMBAD	data
SIMBAD	data

Delta Boötis, Latinized from δ Boötis, is a double star in the northern constellation of Boötes, forming the easternmost member of the constellation's kite-shaped asterism of brighter stars.^[14] Based upon parallax measurements, it is located at a distance of approximately 120.5 light-years (36.9 parsecs) from the Earth.^[1] This star is sometimes called Princeps /ˈprɪnsɛps/,^[15] meaning prince or prime in Latin. The origin of this name is unclear, although it usually appears in an astrological context.^[16]^[17] The apparent visual magnitude of this star is 3.5,^[2] making it visible to the naked eye even during a Full Moon. The magnitude 7.81^[4] companion can be viewed in binoculars or a small telescope.^[14]

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.^[18] Consequently, the Chinese name for δ Boötis itself is 七公七 (Qī Gōng qī, English: the Seventh Star of Seven Excellencies.)^[19]

Properties

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). If they are gravitationally bound to each other, the orbital period of the system would be at least 120,000 years.^[20]

The brighter member of the pair has a stellar classification of G8 III,^[5] 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 eleven times the radius of the Sun.^[9] 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 4,810 K,^[10] which is what gives it the characteristic yellow hue of a G-type star.^[21]

The secondary component has a stellar classification of G0 V,^[4] 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,^[4] making it much less luminous than the primary component.^[22]

References

^ ^a ^b ^c ^d ^e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^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
^ ^a ^b ^c ^d ^e ^f ^g Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
^ ^a ^b ^c ^d ^e ^f ^g 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
^ ^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, S2CID 119468042
^ Soubiran, C.; et al. (2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788, S2CID 16602121.
^ 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.
^ ^a ^b ^c ^d ^e Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", Astronomical Journal, 150 (3), 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114.
^ ^a ^b Baines, Ellyn K.; Thomas Armstrong, J.; Clark, James H.; Gorney, Jim; Hutter, Donald J.; Jorgensen, Anders M.; Kyte, Casey; Mozurkewich, David; Nisley, Ishara; Sanborn, Jason; Schmitt, Henrique R.; Van Belle, Gerard T. (2021), "Angular Diameters and Fundamental Parameters of Forty-four Stars from the Navy Precision Optical Interferometer", The Astronomical Journal, 162 (5): 198, arXiv:2211.09030, Bibcode:2021AJ....162..198B, doi:10.3847/1538-3881/ac2431
^ ^a ^b ^c ^d ^e Soubiran, C.; Creevey, O. L.; Lagarde, N.; Brouillet, N.; Jofré, P.; Casamiquela, L.; Heiter, U.; Aguilera-Gómez, C.; Vitali, S.; Worley, C.; de Brito Silva, D. (2024-02-01), "Gaia FGK benchmark stars: Fundamental Teff and log g of the third version", Astronomy and Astrophysics, 682: A145, Bibcode:2024A&A...682A.145S, doi:10.1051/0004-6361/202347136, ISSN 0004-6361 Delta Boo's database entry at VizieR.
^ 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
^ ^a ^b "del Boo". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-06-14.
^ "BD+33 2562". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-06-14.
^ ^a ^b English, Neil (May 14, 2014), Grab 'n' Go Astronomy, Springer New York, p. 214, Bibcode:2014gnga.book.....E, ISBN 9781493908264.
^ "princeps". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ Robson, Vivian E. (2005), The Fixed Stars and Constellations in Astrology, Astrology Center of America, p. 112, ISBN 1-933303-13-1
^ "Princeps – Constellations of Words". Retrieved 2022-10-28.
^ (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.
^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日 Archived 2011-05-22 at the Wayback Machine
^ Kaler, James B., "DELTA BOO (Delta Bootis)", Stars, University of Illinois, retrieved 2012-01-05
^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
^ The actual brightness ratio is given by 2.512^Δm, 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.