Zeta Sagittarii
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 02m 36.73024s |
| Declination | −29° 52′ 48.2279″ |
| Apparent magnitude (V) | +2.59 (3.27 (A) / 3.48 (B)) |
| Characteristics | |
| Spectral type | A2.5 Va |
| U−B color index | +0.05 |
| B−V color index | +0.08 |
| Astrometry | |
| Radial velocity (Rv) | +22 km/s |
| Proper motion (μ) | RA: +10.79 mas/yr Dec.: +21.11 mas/yr |
| Parallax (π) | 36.98±0.87 mas |
| Distance | 88 ± 2 ly (27.0 ± 0.6 pc) |
| Absolute magnitude (MV) | 1.11 (A)/1.32 (B) |
| Orbit | |
| Primary | Aa |
| Companion | Ab |
| Period (P) | 1 month |
| Semi-major axis (a) | 0.3 au |
| Orbit | |
| Primary | A |
| Companion | B |
| Period (P) | 21.00 ± 0.01 years |
| Semi-major axis (a) | 0.489 ± 0.001" (13.2 au) |
| Eccentricity (e) | 0.211 ± 0.001 |
| Inclination (i) | 111.1 ± 0.1° |
| Longitude of the node (Ω) | 74.0 ± 0.1° |
| Periastron epoch (T) | 2005.99 ± 0.03 |
| Argument of periastron (ω) (secondary) | 7.2 ± 0.6° |
| Details | |
| Aa | |
| Mass | 1.83 M☉ |
| Radius | 1.9 R☉ |
| Luminosity | 14.9 L☉ |
| Surface gravity (log g) | 3.90 cgs |
| Temperature | 8,230 K |
| Rotational velocity (v sin i) | 77 km/s |
| Age | 700 Myr |
| Ab | |
| Mass | 1.81 M☉ |
| Radius | 1.9 R☉ |
| Luminosity | 14.7 L☉ |
| Temperature | 8,200 K |
| Age | 700 Myr |
| B | |
| Mass | 2.03 M☉ |
| Radius | 2.3 R☉ |
| Luminosity | 24 L☉ |
| Temperature | 8,460 K |
| Age | 700 Myr |
| Other designations | |
| Ascella, ζ Sagittarii, ζ Sgr, Zeta Sgr, 38 Sagittarii, CCDM J19026-2953AB, CPD−30 5798, GC 26161, HD 176687, HIP 93506, HR 7194, IDS 18562-3001 AB, PPM 269230, SAO 187600, WDS J19026-2953AB | |
| Database references | |
| SIMBAD | data |
Zeta Sagittarii (ζ Sagittarii, abbreviated Zeta Sgr, ζ Sgr) is a triple star system and the third-brightest star in the constellation of Sagittarius after Kaus Australis and Nunki. Based upon parallax measurements, it is about 88 light-years (27 parsecs) from the Sun.
The three components are designated Zeta Sagittarii Aa (officially named Ascella /əˈsɛlə/, the traditional name for the entire system), Ab and B. The Washington Double Star Catalog cites a component separated 72.3" from the system, but it is a background star unrelated to the pair.