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Theta Boötis
	; θ Boötis in optical light
	Location of θ Boötis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Boötes
Right ascension	14h 25m 11.79695s
Declination	+51° 51′ 02.6772″
Apparent magnitude (V)	4.05 + 13.23
Characteristics
Spectral type	F7 V + M2.5V
U−B color index	−0.02
B−V color index	+0.50
Astrometry
Radial velocity (Rv)	−10.627±0.0065 km/s
Proper motion (μ)	RA: −235.97 mas/yr ; Dec.: −399.696 mas/yr
Parallax (π)	69.0686 ± 0.1579 mas
Distance	47.2 ± 0.1 ly ; (14.48 ± 0.03 pc)
Absolute magnitude (MV)	3.25
Details
A
Mass	1.41; 1.24 M☉
Radius	1.4±0.15 R☉
Luminosity	4.131±0.096 L☉
Surface gravity (log g)	4.07 cgs
Temperature	6,294±40 K
Metallicity [Fe/H]	0.03 dex
Rotational velocity (v sin i)	29.2 km/s
Age	3.1 Gyr; 3.83 Gyr
B
Mass	0.4–0.48 M☉
Radius	0.4013±0.012 R☉
Other designations
	Asellus Primus, θ Boo, 23 Boötis, NSV 6669, BD+52° 1804, FK5 531, GJ 549, HD 126660, HIP 70497, HR 5404, SAO 29137, WDS J14252+5151A, LTT 14245
Database references
SIMBAD	data
ARICNS	data

Theta Boötis, Latinized from θ Boötis, is a star in the northern constellation of Boötes the herdsman, forming a corner of the upraised left hand of this asterism.^[15] It has the traditional name Asellus Primus (/əˈsɛləs ˈpraɪməs/; Latin for "first donkey colt")^[15] and the Flamsteed designation 23 Boötis. Faintly visible to the naked eye, this star has a yellow-white hue with an apparent visual magnitude of 4.05.^[2] It is located at a distance of 47.2 light years from the Sun based on parallax,^[1] but is drifting closer with a radial velocity of −10.6 km/s.^[5]

Properties

The stellar classification of Theta Boötis is F7 V,^[2] matching an F-type main-sequence star. It is a solar-type star that may be near the end of its main sequence lifetime based on a high luminosity for a star of its type.^[12] Theta Boötis is a suspected variable star^[16] and a source of X-ray emission.^[17] There is evidence for low amplitude radial velocity variation of about 5 km/s.^[12] The star has a 24/41% greater mass and a 40% larger radius than the Sun.^[7]^[8]^[9] It is about 3–4 billion years old and is spinning with a projected rotational velocity of 29 km/s.^[11] The star is radiating 4.1^[10] times the luminosity of the Sun from its photosphere at an effective temperature of 6,294 K.^[8]

There is a nearby 11th magnitude optical companion star about 70 arcseconds away. This is a class M2.5 red dwarf that is separated by a minimum of 1,000 AUs. It is uncertain whether they are gravitationally bound, but they do have a common motion through space and so the two stars probably share a common origin.^[18]^[3]

Nomenclature

θ Boötis, along with the other Aselli (ι Boo and κ Boo) and λ Boo, were Aulād al Dhiʼbah (أولاد الضّباع - awlād al-ḍibā‘), "the Whelps of the Hyenas".^[15]

In Chinese, 天枪 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of θ Boötis, κ² Boötis and ι Boötis.^[19] Consequently, the Chinese name for θ Boötis itself is 天枪三 (Tiān Qiāng sān, English: the Third Star of Celestial Spear.)^[20]

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 ^e Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
^ ^a ^b ^c Lépine, Sébastien; Bongiorno, Bethany (March 2007), "New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems", The Astronomical Journal, 133 (3): 889–905, arXiv:astro-ph/0610605, Bibcode:2007AJ....133..889L, doi:10.1086/510333, S2CID 16800796.
^ Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data. SIMBAD, Bibcode:1986EgUBV........0M
^ ^a ^b Soubiran, C.; et al. (2018), "Gaia Data Release 2. The catalogue of radial velocity standard stars", Astronomy and Astrophysics, 616: A7, arXiv:1804.09370, Bibcode:2018A&A...616A...7S, doi:10.1051/0004-6361/201832795, S2CID 52952408.
^ Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191, S2CID 118577511.
^ ^a ^b Tokovinin, A.; Kiyaeva, O. (February 21, 2016), "Eccentricity distribution of wide binaries", Monthly Notices of the Royal Astronomical Society, 456 (2): 2070–2079, arXiv:1512.00278, Bibcode:2016MNRAS.456.2070T, doi:10.1093/mnras/stv2825.
^ ^a ^b ^c ^d ^e ^f ^g Luck, R. Earle (January 2017), "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants", The Astronomical Journal, 153 (1): 19, arXiv:1611.02897, Bibcode:2017AJ....153...21L, doi:10.3847/1538-3881/153/1/21, S2CID 119511744, 21.
^ ^a ^b Baines, Ellyn K.; Clark, James H., III; Schmitt, Henrique R.; Stone, Jordan M.; von Braun, Kaspar (2023-12-01). "33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble". The Astronomical Journal. 166 (6): 268. Bibcode:2023AJ....166..268B. doi:10.3847/1538-3881/ad08be. ISSN 0004-6256.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ ^a ^b Boyajian, Tabetha S.; et al. (February 2012), "Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars", The Astrophysical Journal, 746 (1): 101, arXiv:1112.3316, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101, S2CID 18993744.. See Table 10.
^ ^a ^b Schröder, C.; Reiners, Ansgar; Schmitt, Jürgen H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377^{[permanent dead link]}
^ ^a ^b ^c Rachford, Brian L.; Foight, Dillon R. (June 2009), "Chromospheric Variability in Early F-Type Stars", The Astrophysical Journal, 698 (1): 786–802, arXiv:0904.1620, Bibcode:2009ApJ...698..786R, doi:10.1088/0004-637X/698/1/786, S2CID 693296.
^ ^a ^b Schweitzer, A.; et al. (May 2019). "The CARMENES search for exoplanets around M dwarfs. Different roads to radii and masses of the target stars". Astronomy & Astrophysics. 625: 16. arXiv:1904.03231. Bibcode:2019A&A...625A..68S. doi:10.1051/0004-6361/201834965. S2CID 102351979. A68.
^ "tet Boo". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 January 2018.
^ ^a ^b ^c Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 105, ISBN 0-486-21079-0, retrieved 2010-12-12.
^ Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
^ Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009), "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources", The Astrophysical Journal Supplement, 184 (1): 138–151, arXiv:0910.3229, Bibcode:2009ApJS..184..138H, doi:10.1088/0067-0049/184/1/138, S2CID 119267456.
^ Kaler, James, "Asellus Primus", Stars, University of Illinois, retrieved 2016-01-07.
^ (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) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-11 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.