Theta Boötis
Star in the northern constellation of Boötes
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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]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| 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
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]