61 Cygni
61 Cygni /ˈsɪɡni/ is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years. Of apparent magnitude 5.20 and 6.05, respectively, they can be seen with binoculars in city skies or with the naked eye in rural areas without light pollution.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus |
| 61 Cygni A | |
| Right ascension | 21h 06m 53.9396s |
| Declination | +38° 44′ 57.902″ |
| Apparent magnitude (V) | 5.21 |
| 61 Cygni B | |
| Right ascension | 21h 06m 55.2638s |
| Declination | +38° 44′ 31.359″ |
| Apparent magnitude (V) | 6.05 |
| Characteristics | |
| 61 Cyg A | |
| Spectral type | K5V |
| U−B color index | +1.155 |
| B−V color index | +1.139 |
| Variable type | BY Dra |
| 61 Cyg B | |
| Spectral type | K7V |
| U−B color index | +1.242 |
| B−V color index | +1.320 |
| Variable type | Flare star |
| Astrometry | |
| 61 Cygni A | |
| Radial velocity (Rv) | −65.97±0.12 km/s |
| Proper motion (μ) | RA: 4,164.209 mas/yr Dec.: 3,249.614 mas/yr |
| Parallax (π) | 285.9949 ± 0.0599 mas |
| Distance | 11.404 ± 0.002 ly (3.4966 ± 0.0007 pc) |
| Absolute magnitude (MV) | 7.506 |
| 61 Cygni B | |
| Radial velocity (Rv) | −64.59±0.12 km/s |
| Proper motion (μ) | RA: 4,105.976 mas/yr Dec.: 3,155.942 mas/yr |
| Parallax (π) | 286.0054 ± 0.0289 mas |
| Distance | 11.404 ± 0.001 ly (3.4964 ± 0.0004 pc) |
| Absolute magnitude (MV) | 8.228 |
| Orbit | |
| Companion | 61 Cygni B |
| Period (P) | 678 ±34 yr |
| Semi-major axis (a) | 24.272 ±0.592″ |
| Eccentricity (e) | 0.49 ±0.03 |
| Inclination (i) | 51 ±2° |
| Longitude of the node (Ω) | 178 ±2° |
| Periastron epoch (T) | 1709 ±16 |
| Argument of periastron (ω) (secondary) | 149 ±6° |
| Details | |
| 61 Cygni A | |
| Mass | 0.70 M☉ |
| Radius | 0.665 ±0.005 R☉ |
| Luminosity | 0.153 ±0.01 L☉ |
| Surface gravity (log g) | 4.40 cgs |
| Temperature | 4,526 ±66 K |
| Metallicity [Fe/H] | –0.20 dex |
| Rotation | 35.54±0.47 d |
| Age | 6.1 ±1 Gyr |
| 61 Cygni B | |
| Mass | 0.63 M☉ |
| Radius | 0.595 ±0.008 R☉ |
| Luminosity | 0.085 ±0.007 L☉ |
| Surface gravity (log g) | 4.20 cgs |
| Temperature | 4,077 ±59 K |
| Metallicity [Fe/H] | –0.27 dex |
| Rotation | 34.55±0.57 d |
| Age | 6.1 ±1 Gyr |
| Other designations | |
| 61 Cygni A: V1803 Cygni, HD 201091, HIP 104214, HR 8085, BD+38°4343, LHS 62, SAO 70919 | |
| 61 Cygni B: HD 201092, HIP 104217, HR 8086, BD+38°4344, LHS 63 | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
61 Cygni first attracted the attention of astronomers when its large proper motion was first demonstrated by Giuseppe Piazzi in 1804. In 1838, Friedrich Bessel measured its distance from Earth at about 10.4 light-years, very close to the actual value of about 11.4 light-years; this was the first distance estimate for any star other than the Sun, and first star to have its stellar parallax measured. Among all stars or stellar systems listed in the modern Hipparcos Catalogue, 61 Cygni has the seventh-highest proper motion, and the highest among all visible stars or systems.
Over the course of the twentieth century, several different astronomers reported evidence of a massive planet orbiting one of the two stars, but recent high-precision radial velocity observations have shown that all such claims were unfounded. No planets have been confirmed in this stellar system to date.