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[1] |
| Declination | –29° 52′ 48.2279″[1] |
| Apparent magnitude (V) | +2.59[2] (3.27/3.48)[3] |
| Characteristics | |
| Spectral type | A2.5 Va[4] |
| U−B color index | +0.05[2] |
| B−V color index | +0.08[2] |
| Astrometry | |
| Radial velocity (Rv) | +22[5] km/s |
| Proper motion (μ) | RA: +10.79[1] mas/yr Dec.: +21.11[1] mas/yr |
| Parallax (π) | 36.98 ± 0.87[1] mas |
| Distance | 88 ± 2 ly (27.0 ± 0.6 pc) |
| Absolute magnitude (MV) | 1.11/1.32[3] |
| Orbit[3] | |
| 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 | |
| Surface gravity (log g) | 3.90[6] cgs |
| Temperature | 8,799[6] K |
| Rotational velocity (v sin i) | 77[7] km/s |
| Other designations | |
Zeta Sagittarii (Zeta Sgr, ζ Sagittarii, ζ Sgr) is the third brightest star system in the constellation Sagittarius, with an apparent visual magnitude of +2.59.[2] It has the traditional name Ascella. Based upon parallax measurements, the distance to Ascella is about 88 ly (27 pc).[1] Ascella is moving away from the Solar System with a radial velocity of 22 km s−1.[5] Some 1.0–1.4 million years ago, this system came within 7.5 ± 1.8 ly (2.30 ± 0.55 pc) of the Sun.[8]
This is a binary star system, with the two components orbiting each other over a period of 21 years at an eccentricity of 0.211. The combined mass of the system is 5.26 ± 0.37 times the mass of the Sun[3] and their blended stellar classification is A2.5 Va.[4]
The system consists of a spectral class A2 giant with an apparent magnitude of +3.27, and an A4 subgiant with apparent magnitude of +3.48. The pair have a mean separation of 13.4 astronomical units (AU).[9] Ascella has a faint, 10th magnitude companion, separated from the primary by a distance of 75 arcseconds.
Name and etymology
- The name Ascella from a Late Latin word meaning armpit.
- This star, together with :
- γ Sgr, δ Sgr, ε Sgr, λ Sgr, σ Sgr, τ Sgr and φ Sgr comprising the asterism Teapot.[10][11]
- φ Sgr, σ Sgr, χ Sgr and τ Sgr were Al Naʽām al Ṣādirah (النعم السادرة), the Returning Ostriches.[12]
- σ Sgr and π Sgr may have been the Akkadian Gu-shi-rab‑ba, the Yoke of the Sea.[12]
- τ Sgr, ν Sgr, ψ Sgr, ω Sgr and 60 Sgr were Al Udḥiyy, the Ostrich's Nest.[12]
- 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.[13]
- In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of ζ Sagittarii, φ Sagittarii, λ Sagittarii, μ Sagittarii, σ Sagittarii and τ Sagittarii. Consequently, ζ Sagittarii itself is known as 斗宿一 (Dǒu Sù yī, English: the First Star of Dipper.)[14]
Namesakes
- USS Ascella (AK-137) was a United States Navy Crater class cargo ship named after the star.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 3.0 3.1 3.2 3.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 4.0 4.1 4.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 6.0 6.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ skywatchers[dead link]
- ↑ 12.0 12.1 12.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
