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 | |
Spectral type | M2II + B9.5V[4] |
U−B color index | +0.98[5] |
B−V color index | +1.40[5] |
Variable type | LB?[6] |
Astrometry | |
Radial velocity (Rv) | 2.5 ± 0.9[7] km/s |
Proper motion (μ) | RA: -6.514[1] mas/yr Dec.: 0.849[1] mas/yr |
Parallax (π) | 5.9674 ± 0.2597 mas[8] |
Distance | 550 ± 20 ly (168 ± 7 pc) |
Absolute magnitude (MV) | −2.58[9] |
Orbit[4] | |
Period (P) | 10.11 yr |
Semi-major axis (a) | 0.051″ |
Eccentricity (e) | 0.44 |
Inclination (i) | 140.0° |
Longitude of the node (Ω) | 170.2° |
Periastron epoch (T) | 1979.93 |
Argument of periastron (ω) (secondary) | 257.7° |
Details | |
δ Sge A | |
Mass | 3.35+0.335 −0.30[10] M☉ |
Radius | 108[11] R☉ |
Luminosity | 1,888 - 1,923[11] L☉ |
Surface gravity (log g) | 0.74 ± 0.10[10] cgs |
Temperature | 3,660±170[11] K |
δ Sge B | |
Mass | 2.9[4] M☉ |
Radius | 2.6[4] R☉ |
Luminosity | 63[4] L☉ |
Temperature | 10000[4] K |
Other designations | |
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.[6]
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.[13][better source needed]
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.)[14]