81 Cancri
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cancer |
| Right ascension | 09h 12m 17.547s |
| Declination | +14° 59′ 45.78″ |
| Apparent magnitude (V) | 6.49 |
| Characteristics | |
| Spectral type | G8V + K1V / L8 + ~L8 |
| B−V color index | 0.731±0.004 |
| Variable type | Constant |
| Astrometry | |
| Radial velocity (Rv) | 49.8252±0.076 km/s |
| Proper motion (μ) | RA: −523.619 mas/yr Dec.: +244.282 mas/yr |
| Parallax (π) | 49.1493±0.3467 mas |
| Distance | 66.4 ± 0.5 ly (20.3 ± 0.1 pc) |
| Absolute magnitude (MV) | +4.95 |
| Orbit | |
| Primary | 81 Cancri A |
| Name | 81 Cancri B |
| Period (P) | 988.058±0.34698 d |
| Semi-major axis (a) | 115.4±0.63″ |
| Eccentricity (e) | 0.433256±0.0034 |
| Inclination (i) | 124.1±0.64° |
| Longitude of the node (Ω) | 317.6±0.46° |
| Periastron epoch (T) | 1982.690±0.0040 |
| Argument of periastron (ω) (secondary) | 170.731±0.81° |
| Argument of periastron (ω) (primary) | 350.731±0.81° |
| Semi-amplitude (K1) (primary) | 11.4908±0.11 km/s |
| Semi-amplitude (K2) (secondary) | 12.1317±0.14 km/s |
| Details | |
| 81 Cnc A | |
| Mass | 0.89±0.029 M☉ |
| Radius | 0.82 R☉ |
| Luminosity | 1.03 L☉ |
| Surface gravity (log g) | 4.55 cgs |
| Temperature | 5,430 K |
| Metallicity [Fe/H] | −0.28 dex |
| 81 Cnc B | |
| Mass | 0.85±0.026 M☉ |
| Radius | 0.81 R☉ |
| Surface gravity (log g) | 4.56 cgs |
| Temperature | 5,360 K |
| Metallicity [Fe/H] | −0.28 dex |
| Other designations | |
| π1 Cnc, 81 Cancri, GJ 337, HD 79096, HIP 45170, SAO 98427, WDS J09123+1500 | |
| Database references | |
| SIMBAD | data |
81 Cancri is a stellar system in the zodiac constellation of Cancer. It has the Bayer designation Pi1 Cancri, which is Latinized from π1 Cancri, and abbreviated Pi1 Cnc or π1 Cnc; 81 Cancri is the star's Flamsteed designation. The main component of the system is a close binary, while a brown dwarf binary is located at a wide separation. The primary is just bright enough to be visible to the naked eye, having an apparent visual magnitude of 6.49. Its position near the ecliptic means it is subject to lunar occultations.
Based on parallax measurements, this system is located at a distance of 66 light-years (20 pc) from the Sun. HD 164595 has a large proper motion, traversing the celestial sphere at an angular rate of 0.578″ yr−1. It is drifting further away with a line of sight velocity of 49.8 km/s.