Zeta Sagittarii
 Location of ζ Sagittarii (circled) near the center |
|
| 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 (3.27/3.48) |
| 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 ± 0.87mas |
| Distance | 88 ± 2 ly (27.0 ± 0.6 pc) |
| Absolute magnitude (MV) | 1.11/1.32 |
| Orbit | |
| Period (P) | 21.00 ± 0.01 years |
| Semi-major axis (a) | 0.489 ± 0.001″ |
| 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 | |
| Mass | 5.26 ± 0.37 M☉ |
| Surface gravity (log g) | 3.90 cgs |
| Temperature | 8,799 K |
| Rotational velocity (v sin i) | 77 km/s |
| Age | 500 - 710 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Zeta Sagittarii (ζ Sagittarii, abbreviated Zeta Sgr, ζ Sgr), also named Ascella, is a binary star and the third-brightest star in the constellation of Sagittarius. Based upon parallax measurements, it is about 88 ly (27 pc) from the Sun.
ζ Sagittarii (Latinised to Zeta Sagittarii) is the system's Bayer designation.
It bore the traditional name Ascella, from a Late Latin word meaning armpit. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Thalath al Sadirah, which was translated into Latin as Tertia τού al Sadirah, meaning third returning ostrich. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Ascella for this star on 12 September 2016 and it is now so entered in the IAU Catalog of Star Names.
This star, together with Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii, Lambda Sagittarii, Sigma Sagittarii, Tau Sagittarii and Phi Sagittarii comprise the Teapot asterism.
In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of Zeta Sagittarii, Phi Sagittarii, Lambda Sagittarii, Mu Sagittarii, Sigma Sagittarii and Tau Sagittarii. Consequently, Zeta Sagittarii itself is known as 斗宿一 (Dǒu Sù yī, English: the First Star of Dipper.)
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