Zeta Sagittae

Zeta Sagittae (ζ Sagittae) is triple star^[3] system in the northern constellation of Sagitta. It is visible to the naked eye, having a combined apparent visual magnitude of +5.00.^[2] Based upon an annual parallax shift of 12.79 mas,^[1] the distance to this star is approximately 260 light years.

Zeta Sagittae

Location of ζ Sagittae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Sagitta
Right ascension	19h 48m 58.65978s[1]
Declination	+19° 08′ 31.3516″[1]
Apparent magnitude (V)	+5.00[2] (5.64 + 6.04 + 9.01)[3]
Characteristics
Spectral type	A3 Vnn[4] (A1 V + A3 V)[5]
U−B color index	+0.06[2]
B−V color index	+0.10[2]
Astrometry
Proper motion (μ)	RA: +17.63[1] mas/yr Dec.: +26.27[1] mas/yr
Parallax (π)	12.79±0.67 mas[1]
Distance	260 ± 10 ly (78 ± 4 pc)
Absolute magnitude (MV)	+0.55[6]
Orbit[7]
Period (P)	8487.9±4.9 d
Semi-major axis (a)	0.13605±0.00044″
Eccentricity (e)	0.7948±0.0019
Inclination (i)	132.33±0.41°
Longitude of the node (Ω)	340.97±0.68°
Periastron epoch (T)	44199.6±5.9 HMJD
Argument of periastron (ω) (secondary)	355.3±1.0°
Details
ζ Sge A
Mass	1.80[8] M☉
Radius	1.7[9] R☉
Luminosity	46[10] L☉
Surface gravity (log g)	3.89[8] cgs
Temperature	8,422±286[8] K
Rotational velocity (v sin i)	240[11] km/s
Age	347[8] Myr
Other designations
ζ Sge, 8 Sge, BD+19°4229, GC 27431, HD 187362, HIP 97496, HR 7546, SAO 105298, PPM 137034, ADS 12973, WDS J19490+1909AB[12]
Database references
SIMBAD	data

The inner pair is a visual binary system consisting of two A-type main-sequence stars with an orbital period of 23.2 years (8,487.9 d), a semimajor axis of 0.136 arc seconds, and an eccentricity of 0.79.^[7] The primary, component A, has a visual magnitude of 5.64^[3] with a stellar classification of A3 Vnn,^[4] where the 'nn' suffix indicates "nebulous" lines due to rotation. It is spinning rapidly with a projected rotational velocity of 240 km/s. This is giving the star an oblate shape with an equatorial bulge that is 14% larger than the polar radius.^[11]

The secondary member, component B, is a magnitude 6.04 star, while the more distant component C is magnitude 9.01 and lies at an angular separation of 8.330 arc seconds from the other two.^[3]

Naming

In Chinese, 左旗 (Zuǒ Qí), meaning Left Flag, refers to an asterism consisting of ζ Sagittae, α Sagittae, β Sagittae, δ Sagittae, γ Sagittae, 13 Sagittae, 11 Sagittae, 14 Sagittae and ρ Aquilae. Consequently, the Chinese name for ζ Sagittae itself is 左旗四 (Zuǒ Qí sì, English: the Fourth Star of Left Flag.)^[13]