47 Cygni
Star in the constellation Cygnus
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47 Cygni is a triple star[3][15] system in the northern constellation of Cygnus, and is located around 4,000 light years from the Earth. It is visible to the naked eye with a combined apparent visual magnitude of 4.61.[2] The system is moving closer to the Earth with a heliocentric radial velocity of −4.6 km/s.[6]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 33m 54.18809s[1] |
| Declination | +35° 15′ 03.0390″[1] |
| Apparent magnitude (V) | 4.61[2] (4.84 + 7.30)[3] |
| Characteristics | |
| Spectral type | K6: Ib + B2.5:[2] |
| B−V color index | 1.593±0.023[4] |
| Variable type | Lc[5] |
| Astrometry | |
| Radial velocity (Rv) | −4.6±0.3[6] km/s |
| Proper motion (μ) | RA: −6.12 mas/yr[1] Dec.: −4.166 mas/yr[1] |
| Parallax (π) | 0.8792±0.196 mas[1] |
| Distance | 4072+965 −773 ly (1249+296 −237 pc)[7] |
| Absolute magnitude (MV) | −4.1 (−4 + −1.5)[2] |
| Orbit[8] | |
| Period (P) | 1117±11 d |
| Eccentricity (e) | 0.00 (assumed) |
| Periastron epoch (T) | 2,447,088±10 JD |
| Semi-amplitude (K1) (primary) | 2.0±0.1 km/s |
| Details | |
| 47 Cyg Aa | |
| Mass | 12.1±0.2[9] 19.4±3.9[10] M☉ |
| Radius | 601[11] R☉ |
| Surface gravity (log g) | 1.23[12] cgs |
| Temperature | 4,217[12] K |
| Metallicity [Fe/H] | 0.13[12] dex |
| Age | 17.6±0.6[9] Myr |
| 47 Cyg Ab | |
| Mass | 0.57[13] M☉ |
| 47 Cyg B | |
| Mass | 10.96[13] M☉ |
| Other designations | |
| 47 Cyg, V2125 Cyg, BD+34°4079, GC 28630, HD 196093/196094, HIP 101474, HR 7866, SAO 70203, WDS J20339+3515, 2MASS J20335419+3515031[14] | |
| Database references | |
| SIMBAD | data |
The dual nature of this system was recognized by Annie Cannon in 1912, and she assigned the pair separate Henry Draper Catalogue identifiers.[8] They orbit each other with a period of around 143.69 yr.[13] The primary component is itself a spectroscopic binary in a near circular orbit with a period of around 3.06 yr. The a sin i value for the primary is 30.8 ± 1.6 Gm (0.206 ± 0.011 AU), where a is the semimajor axis and i is the orbital inclination. It has been repeatedly resolved by speckle interferometery since 1973. Radio emission was detected from this system in 1985/86.[8]
The supergiant primary is a slow irregular variable with an amplitude of about 0.1 magnitudes.[5] Its angular diameter has been measured at 4.472±0.017 milliarcseconds using interferometry by the Navy Precision Optical Interferometer.[17] At the distance of 1,249 parsecs,[7] it yield a radius of 601 R☉.[11] Its close companion has 57% of the mass of the Sun.[13] The secondary is a hot B-type main-sequence star, but still 2.5 magnitudes fainter than the primary.[3]
It was once designated l Cygni (lowercase L) by John Flamsteed and was included in his Atlas Coelestis, but the designation is now dropped.[18]
