Delta Sagittae
Binary star system in the constellation Sagitta
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Delta Sagittae (Delta Sge, δ Sagittae, δ Sge) is a binary star in the constellation of Sagitta, with an apparent magnitude of +3.68. The primary component is a red M-type bright giant, and the secondary is a B-type main-sequence star.[2] It is approximately 430 light years from Earth, based on its Gaia Data Release 2 parallax.[1]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagitta |
| Right ascension | 19h 47m 23.26653s[1] |
| Declination | +18° 32′ 03.5203″[1] |
| Apparent magnitude (V) | +3.82[2](3.91[3]/ 6.64)[4] |
| Characteristics | |
| Evolutionary stage | AGB + main sequence[5] |
| Spectral type | M2II + B9.5V[4] |
| U−B color index | +0.98[6] |
| B−V color index | +1.40[6] |
| Variable type | LB?[7] |
| Astrometry | |
| Radial velocity (Rv) | 2.5 ± 0.9[8] km/s |
| Proper motion (μ) | RA: -6.514[1] mas/yr Dec.: 0.849[1] mas/yr |
| Parallax (π) | 5.9674±0.2597 mas[9] |
| Distance | 550 ± 20 ly (168 ± 7 pc) |
| Absolute magnitude (MV) | −2.58[10] |
| Orbit[11] | |
| Period (P) | 3,703.7±1.5 days |
| Semi-major axis (a) | (5.50±0.04)×108 km[a] |
| Eccentricity (e) | 0.441±0.005 |
| Inclination (i) | 40° |
| Longitude of the node (Ω) | 170.2[4]° |
| Periastron epoch (T) | 1979.93[4] |
| Argument of periastron (ω) (secondary) | 263.9±1.0° |
| Details | |
| δ Sge A | |
| Mass | 3.8[11] M☉ |
| Radius | 180±25[11] R☉ |
| Luminosity | 3,162[4] L☉ |
| Surface gravity (log g) | 0.74±0.10[5] cgs |
| Temperature | 3,660±170[12] K |
| δ Sge B | |
| Mass | 3.611[13] M☉ |
| Radius | 3.3 – 4.7[13] R☉ |
| Luminosity | 63[4] L☉ |
| Temperature | 10,000[4] K |
| Other designations | |
| δ Sagittae, 7 Sagittae, BD+18 4240, CCDM J19474+1832AB, FK5 743, GC 27391, HD 187076, HIP 97365, HR 7536, IDS 19429+1817 AB, PPM 136976, SAO 105259, WDS J19474+1832AB | |
| Database references | |
| SIMBAD | data |
Delta Sagittae is a spectroscopic binary with a composite spectrum, meaning that light from both stars can be detected. It has an orbital period of about 10 years and an eccentricity of about 0.44.[4] It is also a variable star, with its brightness changing between a maximum of magnitude 3.75 and a minimum of 3.83 in an unpredictable way.[7]
Delta Sagittae is moving through the Galaxy at a speed of 9.8 km/s relative to the Sun. Its projected Galactic orbit carries it between 23,800 and 35,300 light years from the center of the Galaxy.[15][better source needed]
Naming
In Chinese, 左旗 (Zuǒ Qí), meaning Left Flag, refers to an asterism consisting of δ Sagittae, α Sagittae, β Sagittae, ζ Sagittae, γ Sagittae, 13 Sagittae, 11 Sagittae, 14 Sagittae and ρ Aquilae. Consequently, the Chinese name for δ Sagittae itself is 左旗三 (Zuǒ Qí sān, English: the Third Star of Left Flag.)[16]
Notes
- calculated from a sin i divided by the sine of inclination.