Iota1 Librae
Multiple star system in the constellation Libra
From Wikipedia, the free encyclopedia
Iota1 Librae is a quadruple[4] star system in the constellation Libra. Its name is a Bayer designation that is Latinized from ι1 Librae, and abbreviated Iota1 Lib or ι1 Lib. Its apparent magnitude is 4.54. It is located 379 light years from earth.[8]
(5.1 + 5.6 + 10.4 + 10.9)[3]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Libra |
| Right ascension | 15h 12m 13.29025s[1] |
| Declination | −19° 47′ 30.1592″[1] |
| Apparent magnitude (V) | +4.54[2] (5.1 + 5.6 + 10.4 + 10.9)[3] |
| Characteristics | |
| Spectral type | B9IVpSi + B9[4] + G5IV[3] |
| U−B color index | −0.38[2] |
| B−V color index | −0.08[2] |
| Variable type | Alpha2 Canum Venaticorum |
| Astrometry | |
| Radial velocity (Rv) | −11.6[2] km/s |
| Proper motion (μ) | RA: −35.40[1] mas/yr Dec.: −32.79[1] mas/yr |
| Parallax (π) | 8.59±0.25 mas[1] |
| Distance | 380 ± 10 ly (116 ± 3 pc) |
| Absolute magnitude (MV) | −0.79[5] |
| Position (relative to A)[3] | |
| Component | BC |
| Angular distance | 57.8″ |
| Position angle | 111° |
| Orbit[6] | |
| Primary | Aa |
| Name | Ab |
| Period (P) | 23.512±0.026 yr |
| Semi-major axis (a) | 0.12932±0.00064″ |
| Eccentricity (e) | 0.2440±0.0029 |
| Inclination (i) | 154.2±1.0° |
| Longitude of the node (Ω) | 173.8±2.3° |
| Periastron epoch (T) | 1971.034±0.076 |
| Argument of periastron (ω) (secondary) | 340.1±2.8° |
| Semi-amplitude (K1) (primary) | 3.4[7] km/s |
| Position (relative to B)[3] | |
| Component | C |
| Angular distance | 2.058″ |
| Position angle | 111° |
| Details[3] | |
| Aa | |
| Mass | 3.61 M☉ |
| Ab | |
| Mass | 3.12 M☉ |
| B | |
| Mass | 0.98 M☉ |
| C | |
| Mass | 0.91 M☉ |
| Other designations | |
| ι1 Lib, 24 Librae, BD−19°4047, HD 134759, HIP 74392, HR 5652, SAO 159090, WDS J15122-1948A[2] | |
| Database references | |
| SIMBAD | data |
Visibility
Due to its southern location, although the star can be seen from most regions of the earth, observers in the southern hemisphere are more advantaged. Near Antarctica, it appears circumpolar, while it always remains invisible only in the vicinity of the Arctic Circle. Its magnitude of 4.5 means that naked eye visibility is dependent on a sky sufficiently free from the effects of light pollution.
The best time for observation in the evening sky falls in the months between May and September; from both hemispheres of the period of visibility remains approximately the same, thanks to the position of the star not far from the celestial equator.
Physical
Iota1 Librae is a quadruple star system.[4] The inner pair, designated components Aa and Ab, form a spectroscopic binary[7] with an orbital period of 23.512 years and an eccentricity of 0.2440.[6] The brighter member has a stellar classification of B9 IVp Si,[4] indicating it is a B-type subgiant star with an overabundance of silicon in the photosphere. It is a variable star of the Alpha2 Canum Venaticorum type with a magnitude that varies from 4.53 to 4.56, while its spectrum likewise shows variability.[10] The secondary component is of class B9.[4] The two stars are very close together (0.129 arcsec away), respectively of magnitude 5.10 and 5.60.[3]
The two other stars are the components C and D; separated by 57.8" from AB and 2.058" from each other. The combined spectrum is G5IV, and each star has masses of 0.98 and 0.91 solar masses, and magnitudes 10.40 and 10.90, respectively.[3]
Due to its position on the ecliptic, it is sometimes obscured by the Moon or planets. A lunar occultation took place April 4, 2012.[11]