Pi2 Cygni
Star system in the constellation Cygnus
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Pi2 Cygni, Latinized from π2 Cygni, is a possible 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.
 | |
| 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 Cyg, BD+48°3504, FK5 821, HD 207330, HIP 107533, HR 8335, SAO 51293[12] | |
| Database references | |
| SIMBAD | data |
Pi2 Cygni has been described as a single-lined[15] spectroscopic binary with an orbital period of 72.0162 days and an eccentricity of 0.34.[7] However, a 2020 paper found no radial velocity variations on the timescale of the published orbit.[16] 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.[17]
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).[18]