Iota Boötis
Binary star system in the constellation of Boötes
From Wikipedia, the free encyclopedia
Iota Boötis is a wide binary star system in the constellation Boötes, approximately 96 light-years from Earth. Its name is a Bayer designation that is Latinized from ι Boötis, and abbreviated Iota Boo or ι Boo. The brighter component has the traditional name Asellus Secundus, pronounced /əˈsɛləs sɪˈkʌndəs/, which is Latin for "second donkey colt", and the Flamsteed designation 21 Boötis.[13] It is faintly visible to the naked eye with a typical apparent visual magnitude of +4.75.[2] Based on parallax measurements, it is located at a distance of 96 light-years (29 pc) from the Earth. The star is drifting closer to the Sun with a radial velocity of −19 km/s.[7]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Right ascension | 14h 16m 09.930s[1] |
| Declination | +51° 22′ 02.029″[1] |
| Apparent magnitude (V) | 4.75[2] (4.73–4.78[3]) |
| Characteristics | |
| Spectral type | A7 V[4] + K0 V[5] |
| U−B color index | +0.06[6] |
| B−V color index | +0.20[6] |
| R−I color index | +0.09[6] |
| Variable type | Delta Scuti variable[3] |
| Astrometry | |
| Radial velocity (Rv) | −18.7[7] km/s |
| Proper motion (μ) | RA: −149.277 mas/yr[1] Dec.: +89.135 mas/yr[1] |
| Parallax (π) | 33.8856±0.0820 mas[1] |
| Distance | 96.3 ± 0.2 ly (29.51 ± 0.07 pc) |
| Absolute magnitude (MV) | +2.38[8] |
| Details | |
| ι Boo A | |
| Mass | 1.650±0.04[1] M☉ |
| Radius | 1.715+0.055 −0.021[1] R☉ |
| Luminosity | 8.90+0.06 −0.07[1] L☉ |
| Surface gravity (log g) | 4.14+0.01 −0.02[1] cgs |
| Temperature | 7,764+3 −8[1] K |
| Metallicity [Fe/H] | +0.19[9] dex |
| Rotational velocity (v sin i) | 144[10] km/s |
| Age | 785±223[1] Myr |
| HD 234121 | |
| Mass | 0.807+0.042 −0.041[11] M☉ |
| Radius | 0.824±0.017[11] R☉ |
| Luminosity | 0.411+0.051 −0.041[11] L☉ |
| Surface gravity (log g) | 4.511+0.018 −0.005[11] cgs |
| Temperature | 5,090+17 −4[11] K |
| Other designations | |
| Asellus Secondus[12], ι Boötis, 21 Boötis, BD+52°1784, FK5 528, GC 19269, HD 125161, HIP 69713, HR 5350, SAO 29071, PPM 34432, WDS J14162+5122[13] | |
| Database references | |
| SIMBAD | data |
| Data sources: | |
| Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.) | |
The companion is HD 234121, a K-type main-sequence star at an angular distance of 38.6 arcseconds; easily separated with binoculars.
Components
The primary component is a white hued A-type main-sequence star with a stellar classification of A7V.[4] It is classified as a Delta Scuti-type variable star and its brightness varies from magnitude +4.73 to +4.78 with a stable period of 38 minutes.[8] This star is 785[1] million years old and has a high rate of spin, showing a projected rotational velocity of 144 km/s.[10] It has 1.8[4] times the mass of the Sun and 1.7 times the Sun's radius.[1] Iota Boötis is radiating 8.8[1] times the luminosity of the Sun from its photosphere at an effective temperature of 7,764 K.[1]
The common proper motion companion, HD 234121, is a magnitude 7.3 main-sequence star belonging to spectral class K0V.[5][15] It has a projected separation from ι Boo of 1,100 AU.[4] HD 234121 has a mass of 0.8 M☉, a luminosity of 0.4 L☉, a temperature of 5,090 K, and a radius of 0.8 R☉.[11]
The Washington Double Star Catalog lists a third component, a 14th-magnitude star at 90 arcseconds,[15] but it is an unrelated background star.[16]
Nomenclature
This star, along with the other Aselli (θ Boo and κ Boo) and λ Boo, were Aulād al Dhiʼbah (أولاد الضّباع - awlād al-ḍibā‘), "the Whelps of the Hyenas".[the transcription does not match the Arabic][17]
In Chinese, 天槍 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of ι Boötis, κ2 Boötis and θ Boötis.[18] Consequently, the Chinese name for ι Boötis itself is 天槍二 (Tiān Qiāng èr, English: the Second Star of Celestial Spear).[19]