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Binary star system in the constellation Cancer From Wikipedia, the free encyclopedia
Epsilon Cancri (ε Cancri, abbreviated Epsilon Cnc, ε Cnc) is a white-hued binary star system in the zodiac constellation of Cancer. It is the brightest member of the Beehive Cluster[14] with an apparent visual magnitude of +6.29,[2] which is near the lower limit of visibility with the naked eye. The annual parallax shift of 5.4 mas as seen from Earth yields a distance estimate of approximately 606 light-years from the Sun.
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cancer |
| ε Cnc A | |
| Right ascension | 08h 40m 27.01010s[1] |
| Declination | 19° 32′ 41.3243″[1] |
| Apparent magnitude (V) | 6.29[2] |
| HD 73711 | |
| Right ascension | 08h 40m 18.09670s[3] |
| Declination | 19° 31′ 55.1636″[3] |
| Apparent magnitude (V) | 7.535[4] |
| Characteristics | |
| ε Cnc A | |
| Spectral type | A5 III[5] (kA3hA5mF0)[6] |
| U−B color index | +0.16[7] |
| B−V color index | +0.17[7] |
| HD 73711 | |
| Spectral type | F0III[8] (kA3hA5mF0)[9] |
| Astrometry | |
| ε Cnc A | |
| Radial velocity (Rv) | +29.9±1.1[10] km/s |
| Proper motion (μ) | RA: −36.293[1] mas/yr Dec.: −12.133[1] mas/yr |
| Parallax (π) | 5.3836 ± 0.0474 mas[1] |
| Distance | 606 ± 5 ly (186 ± 2 pc) |
| Absolute magnitude (MV) | +0.00[2] |
| HD 73711 | |
| Proper motion (μ) | RA: −36.251[3] mas/yr Dec.: −12.118[3] mas/yr |
| Parallax (π) | 5.4103 ± 0.0308 mas[3] |
| Distance | 603 ± 3 ly (185 ± 1 pc) |
| Orbit[11] | |
| Primary | ε Cnc Aa |
| Companion | ε Cnc Ab |
| Period (P) | 35.14101±0.00005 d |
| Semi-major axis (a) | 1.9127±0.0004 mas |
| Eccentricity (e) | 0.4195±0.0003 |
| Inclination (i) | 81.454±0.010° |
| Longitude of the node (Ω) | 356.069±0.014° |
| Periastron epoch (T) | 2448314.598 ± 0.016 |
| Argument of periastron (ω) (primary) | 258.38±0.02° |
| Semi-amplitude (K1) (primary) | 56.60±0.03 km/s |
| Semi-amplitude (K2) (secondary) | 61.55±0.10 km/s |
| Details | |
| ε Cnc Aa | |
| Mass | 2.420[11] M☉ |
| Radius | 4.8[4] R☉ |
| Luminosity | 90[4] L☉ |
| Surface gravity (log g) | 3.49[12] cgs |
| Temperature | 8,163[4] K |
| Metallicity [Fe/H] | +0.10[12] dex |
| Rotational velocity (v sin i) | 49.2[13] km/s |
| Age | 637 ± 19[11] Myr |
| ε Cnc Ab | |
| Mass | 2.226[11] M☉ |
| HD 73711 | |
| Mass | 2.54[3] M☉ |
| Radius | 2.4[3] R☉ |
| Luminosity | 43.5[3] L☉ |
| Surface gravity (log g) | 4.09[3] cgs |
| Temperature | 9,572[3] K |
| Metallicity [Fe/H] | +0.79[3] dex |
| Rotational velocity (v sin i) | 56.3[8] km/s |
| Age | 407[3] Myr |
| Other designations | |
| ε Cancri: Meleph, ε Cnc, 41 Cancri, BD+20°2171, GC 11904, HD 73731, HIP 42556, HR 3429, SAO 98024, GSC 01395-02733 | |
| HD 73711: BD+20°2163, GC 11893, HD 73711, SAO 98018 | |
| Database references | |
| SIMBAD | ε Cancri |
| HD 73711 | |
The binary pair has the designation WDS J08405+1933. The primary star is designated Epsilon Cancri and the secondary is HD 73711. Epsilon Cancri is itself a spectroscopic binary with components designated Aa (also named Meleph[15]) and Ab. HD 73711 is also suspected of being a spectroscopic binary.[16]
ε Cancri (Latinised to Epsilon Cancri) is the system's Bayer designation, which originally referred to the entire cluster.[17]
In 2016, the IAU organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[19] It approved the name Meleph for the component Epsilon Cancri Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[15]
The system is moving away from the Sun with a radial velocity of +30 km/s.[10]
Epsilon Cancri A is a double-lined spectroscopic binary system with an orbital period of 35.14 days and eccentricity of 0.42.[11] It has a stellar classification of A5 III,[5] which matches an A-type giant star. The spectrum displays the chemically peculiar characteristics of an Am star.[20] Its spectral type has been listed as kA3hA5mF0, indicating the different spectral types shown by spectral lines of calcium, hydrogen, and other metals.[6] Despite the spectral classification, evolutionary models suggest that the star is still on the main sequence, although at the very end of its hydrogen-burning life.[1] The age of the system is estimated to be around 637 million years.[11]
HD 73711 is another Am star, given a stellar classification of F0 III on the basis of its hydrogen absorption lines but a more complete classification of kA3hA5mF0. Although the spectral class would indicate that the star is a giant, models suggest that it is still fusing hydrogen in its core.[3]
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