Iota Boötis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Right ascension | 14h 16m 09.930s |
| Declination | +51° 22′ 02.029″ |
| Apparent magnitude (V) | 4.75 (4.73–4.78) |
| Characteristics | |
| Spectral type | A7 V + K0 V |
| U−B color index | +0.06 |
| B−V color index | +0.20 |
| R−I color index | +0.09 |
| Variable type | Delta Scuti variable |
| Astrometry | |
| Radial velocity (Rv) | −18.7 km/s |
| Proper motion (μ) | RA: −149.277 mas/yr Dec.: +89.135 mas/yr |
| Parallax (π) | 33.8856±0.0820 mas |
| Distance | 96.3 ± 0.2 ly (29.51 ± 0.07 pc) |
| Absolute magnitude (MV) | +2.38 |
| Details | |
| ι Boo A | |
| Mass | 1.650±0.04 M☉ |
| Radius | 1.715+0.055 −0.021 R☉ |
| Luminosity | 8.90+0.06 −0.07 L☉ |
| Surface gravity (log g) | 4.14+0.01 −0.02 cgs |
| Temperature | 7,764+3 −8 K |
| Metallicity [Fe/H] | +0.19 dex |
| Rotational velocity (v sin i) | 144 km/s |
| Age | 785±223 Myr |
| HD 234121 | |
| Mass | 0.807+0.042 −0.041 M☉ |
| Radius | 0.824±0.017 R☉ |
| Luminosity | 0.411+0.051 −0.041 L☉ |
| Surface gravity (log g) | 4.511+0.018 −0.005 cgs |
| Temperature | 5,090+17 −4 K |
| Other designations | |
| Asellus Secondus, ι Boötis, 21 Boötis, BD+52°1784, FK5 528, GC 19269, HD 125161, HIP 69713, HR 5350, SAO 29071, PPM 34432, WDS J14162+5122 | |
| Database references | |
| SIMBAD | data |
| Data sources: | |
| Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.) | |
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. It is faintly visible to the naked eye with a typical apparent visual magnitude of +4.75. 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.
The companion is HD 234121, a K-type main-sequence star at an angular distance of 38.6 arcseconds; easily separated with binoculars.