55 Cancri
55 Cancri is a binary star system located 41 light-years away from the Sun in the zodiac constellation of Cancer. It has the Bayer designation Rho1 Cancri (ρ1 Cancri); 55 Cancri is the Flamsteed designation (abbreviated 55 Cnc). The system consists of a K-type star (designated 55 Cancri A, also named Copernicus /koʊˈpɜːrnɪkəs/) and a smaller red dwarf (55 Cancri B).
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cancer |
| Pronunciation | /ˈkæŋkraɪ/ or /ˈkæŋkriː/ |
| 55 Cancri A | |
| Right ascension | 08h 52m 35.8111s |
| Declination | +28° 19′ 50.955″ |
| Apparent magnitude (V) | 5.95 |
| 55 Cancri B | |
| Right ascension | 08h 52m 40.8627s |
| Declination | +28° 19′ 58.821″ |
| Apparent magnitude (V) | 13.15 |
| Characteristics | |
| 55 Cancri A | |
| Evolutionary stage | Main sequence or subgiant |
| Spectral type | K0IV–V |
| U−B color index | 0.63 |
| B−V color index | 0.87 |
| 55 Cancri B | |
| Evolutionary stage | Main sequence (red dwarf) |
| Spectral type | M4.5V |
| B−V color index | 1.7 |
| Astrometry | |
| 55 Cancri A | |
| Radial velocity (Rv) | 27.51 km/s |
| Proper motion (μ) | RA: −485.681±0.040 mas/yr Dec.: −233.517±0.037 mas/yr |
| Parallax (π) | 79.4482 ± 0.0429 mas |
| Distance | 41.05 ± 0.02 ly (12.587 ± 0.007 pc) |
| Absolute magnitude (MV) | +5.50 |
| 55 Cancri B | |
| Proper motion (μ) | RA: −481.176±0.041 mas/yr Dec.: −244.544±0.032 mas/yr |
| Parallax (π) | 79.6560 ± 0.0475 mas |
| Distance | 40.95 ± 0.02 ly (12.554 ± 0.007 pc) |
| Absolute magnitude (MV) | +12.58±0.088 |
| Details | |
| 55 Cnc A | |
| Mass | 0.905±0.015 M☉ |
| Radius | 0.943±0.010 R☉ |
| Luminosity | 0.582±0.014 L☉ |
| Surface gravity (log g) | 4.45±0.01 cgs |
| Temperature | 5,172±18 K |
| Metallicity [Fe/H] | 0.35±0.10 dex |
| Rotation | 38.8±0.05 days |
| Rotational velocity (v sin i) | <1.23±0.01 km/s |
| Age | 8.6±1 Gyr |
| 55 Cnc B | |
| Mass | 0.264±0.007 M☉ |
| Radius | 0.268±0.009 R☉ |
| Luminosity | 0.00788±0.00013 L☉ |
| Temperature | 3,320±51 K |
| Metallicity [Fe/H] | 0.15±0.16 dex |
| Rotation | 6.11+3.2 −1.9 days |
| Rotational velocity (v sin i) | 2.36 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
| 55 Cnc B | |
| Exoplanet Archive | data |
| ARICNS | data |
As of 2015, five extrasolar planets (designated 55 Cancri b, c, d, e and f; named Galileo, Brahe, Lipperhey, Janssen and Harriot, respectively) are known to orbit 55 Cancri A.
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