Theta Boötis

Theta Boötis is a star in the northern constellation of Boötes the herdsman, forming a corner of the upraised left hand of this asterism.^[13] Its name is a Bayer designation that is Latinized from θ Boötis, and abbreviated Theta Boo or θ Boo. This star has the traditional name Asellus Primus, pronounced /əˈsɛləs ˈpraɪməs/, which is Latin for "first donkey colt".^[13] 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 (14.5 pc) from the Sun based on parallax measurements,^[1] but is drifting closer with a radial velocity of −10.6 km/s.^[5] It has a relatively high proper motion, traversing the celestial sphere at the rate of 0.464 arc seconds per annum.^[14]

Theta Boötis

Location of θ Boötis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Boötes
Right ascension	14h 25m 11.797s[1]
Declination	+51° 51′ 02.68″[1]
Apparent magnitude (V)	4.05[2] + 13.23[3]
Characteristics
Spectral type	F7 V[2] + M2.5V[3]
U−B color index	−0.02[4]
B−V color index	+0.50[2]
Astrometry
Radial velocity (Rv)	−10.627±0.0065[5] km/s
Proper motion (μ)	RA: −235.97 mas/yr[1] Dec.: −399.696 mas/yr[1]
Parallax (π)	69.0686±0.1579 mas[1]
Distance	47.2 ± 0.1 ly (14.48 ± 0.03 pc)
Absolute magnitude (MV)	3.25[6]
Details
A
Mass	1.232±0.012[7] M☉
Radius	1.726±0.012[7] R☉
Luminosity	4.205±0.020[7] L☉
Surface gravity (log g)	4.06±0.02[7] cgs
Temperature	6,292±20[7] K
Metallicity [Fe/H]	0.03[8] dex
Rotational velocity (v sin i)	29.2[9] km/s
Age	3.1 Gyr[10] 3.83[8] Gyr
B
Mass	0.4–0.48[11] M☉
Radius	0.4013±0.012[11] R☉
Luminosity	0.022[11] L☉
Surface gravity (log g)	4.91[11] cgs
Temperature	3,521[11] K
Metallicity [Fe/H]	−0.07[11] dex
Other designations
Asellus Primus, θ Boo, 23 Boötis, NSV 6669, BD+52°1804, FK5 531, GC 19467, GJ 549, HD 126660, HIP 70497, HR 5404, SAO 29137, PPM 34508, WDS J14252+5151A, LTT 14245[12]
Database references
SIMBAD	data
ARICNS	data

Properties

θ Boötis in optical light

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.^[10] Theta Boötis is a suspected variable star^[15] and a source of X-ray emission.^[16] There is evidence for low amplitude radial velocity variation of about 5 km/s.^[10] The star has a magnetic field with a mean longitudinal strength of 147±59 Gauss.^[17]

Theta Boötis has a 23% greater mass and a 73% larger radius than the Sun.^[7] It is about 3–4 billion years old and is spinning with a projected rotational velocity of 29 km/s.^[9] The star is radiating 4.2 times the luminosity of the Sun^[18] from its photosphere at an effective temperature of 6,290 K.^[7] Based on the proportion of iron found in the stellar spectrum, this star has a near-solar abundance of elements with mass greater than helium.^[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 AU. 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.^[19][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".^[13]

In Chinese, 天枪 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of θ Boötis, κ² Boötis and ι Boötis.^[20] Consequently, the Chinese name for θ Boötis itself is 天枪三 (Tiān Qiāng sān, English: the Third Star of Celestial Spear.)^[21]