Pi2 Cygni

Pi² Cygni, Latinized from π² Cygni, is a triple star^[13] system in the northern constellation of Cygnus. It is visible to the naked eye about 2.5° east-northeast of the open cluster M39,^[14] having an apparent visual magnitude of 4.24.^[2] Based upon an annual parallax shift of 2.95 mas,^[1] it is located at a distance of roughly 1,100 light years from the Sun.

For other stars with this Bayer designation, see π Cygni.

Pi² Cygni

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cygnus
Right ascension	21h 46m 47.60832s[1]
Declination	+49° 18′ 34.4511″[1]
Apparent magnitude (V)	4.24[2]
Characteristics
Spectral type	B2.5 III[3]
U−B color index	−0.79[2]
B−V color index	−0.125[2]
Variable type	β Cep[4]
Astrometry
Radial velocity (Rv)	−12.3[5] km/s
Proper motion (μ)	RA: +2.77[1] mas/yr Dec.: −2.00[1] mas/yr
Parallax (π)	2.95±0.34 mas[1]
Distance	approx. 1,100 ly (approx. 340 pc)
Absolute magnitude (MV)	−3.39[6]
Orbit[7]
Period (P)	72.0162 d
Eccentricity (e)	0.34
Periastron epoch (T)	2428410.6 JD
Argument of periastron (ω) (secondary)	238.1°
Semi-amplitude (K1) (primary)	7.8 km/s
Details
π2 Cyg A
Mass	8.4±0.4[8] M☉
Radius	7.1[9] R☉
Luminosity (bolometric)	8,442[10] L☉
Surface gravity (log g)	3.69±0.16[11] cgs
Temperature	20,815±1,057[11] K
Metallicity [Fe/H]	0.04±0.09[11] dex
Rotational velocity (v sin i)	50±5[4] km/s
Age	33.2±5.8[8] Myr
Other designations
π2 Cyg, 81 Cygni, BD+48°3504, FK5 821, HD 207330, HIP 107533, HR 8335, SAO 51293.[12]
Database references
SIMBAD	data

The inner pair of stars in this system form a single-lined^[15] spectroscopic binary with an orbital period of 72.0162 days and an eccentricity of 0.34.^[7] The primary, component A, is a B-type giant star with a stellar classification of B2.5 III.^[3] It is a Beta Cephei variable^[4] with an estimated 8.4^[8] times the mass of the Sun and around 7.1^[9] times the Sun's radius. The star is roughly 33^[8] million years old and is spinning with a projected rotational velocity of 50^[4] km/s. It is radiating 8,442^[10] times the solar luminosity from its outer atmosphere at an effective temperature of around 20,815^[11] K.

The third member of this system is a magnitude 5.98 star at an angular separation of 0.10 arc seconds along a position angle of 129°, as of 1996.^[16]

Historical names

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of π² Cygni, α Lacertae, 4 Lacertae, π¹ Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ψ Andromedae and ι Andromedae. Consequently, the Chinese name for π² Cygni itself is 螣蛇三 (Téng Shé sān, English: the Third Star of Flying Serpent)^[17]