Sigma Librae
Sigma Librae (σ Librae, abbreviated Sigma Lib, σ Lib) is a binary star in the constellation of Libra. The apparent visual magnitude is +3.29, making it visible to the naked eye. Based upon parallax measurements, this system is at a distance of roughly 288 light-years (88 parsecs) from the Sun, with a 2% margin of error. At that distance, the visual magnitude is diminished by 0.20 ± 0.17 from extinction caused by intervening gas and dust.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Libra |
| Right ascension | 15h 04m 04.21608s |
| Declination | –25° 16′ 55.0606″ |
| Apparent magnitude (V) | 3.20 - 3.46 |
| Characteristics | |
| Spectral type | M2.5III |
| U−B color index | +1.94 |
| B−V color index | +1.70 |
| Variable type | SRb |
| Astrometry | |
| Radial velocity (Rv) | –4.2 km/s |
| Proper motion (μ) | RA: –71.16 mas/yr Dec.: −43.34 mas/yr |
| Parallax (π) | 11.31 ± 0.25 mas |
| Distance | 288 ± 6 ly (88 ± 2 pc) |
| Absolute magnitude (MV) | –1.5 |
| Details | |
| Mass | 2.2 M☉ |
| Radius | 108 R☉ |
| Luminosity | 1,820 L☉ |
| Surface gravity (log g) | 0.9 ± 0.3 cgs |
| Temperature | 3,596 K |
| Metallicity [Fe/H] | 0.00 dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
The two components are designated Sigma Librae A (officially named Brachium /ˈbreɪkiəm/, the traditional name for the system) and B.
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