Epsilon Cancri
Binary star system in the constellation Cancer
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Epsilon Cancri is a white-hued multiple star system in the zodiac constellation of Cancer. Its name is a Bayer designation that is Latinized from ε Cancri, and abbreviated Epsilon Cnc or ε Cnc. This is the brightest member of the Beehive Cluster (or Praesepe)[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 (186 pc) from the Sun. The system is moving away from the Sun with a radial velocity of +30 km/s.[10]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| 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] |
| B (HD 73711) | |
| Evolutionary stage | main sequence[3] |
| 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 mas/yr[1] Dec.: −12.133 mas/yr[1] |
| Parallax (π) | 5.3836±0.0474 mas[1] |
| Distance | 606 ± 5 ly (186 ± 2 pc) |
| Absolute magnitude (MV) | +0.00[2] |
| B (HD 73711) | |
| Proper motion (μ) | RA: −36.251 mas/yr[3] Dec.: −12.118 mas/yr[3] |
| Parallax (π) | 5.4103±0.0308 mas[3] |
| Distance | 603 ± 3 ly (185 ± 1 pc) |
| Orbit[11] | |
| Primary | ε Cnc Aa |
| Name | 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[11] | |
| ε Cnc Aa | |
| Mass | 2.420±0.008 M☉ |
| Radius | ~3.8[a] R☉ |
| Luminosity | ~59.8 L☉ |
| Surface gravity (log g) | ~3.6 cgs |
| Temperature | ~8,060 K |
| Metallicity [Fe/H] | ~ +0.2 dex |
| Age | 637±19 Myr |
| ε Cnc Ab | |
| Mass | 2.226±0.004 M☉ |
| Radius | ~2.7[b] R☉ |
| Surface gravity (log g) | ~4.0 cgs |
| Temperature | ~8,330 K |
| Metallicity [Fe/H] | ~ +0.2 dex |
| Age | 637±19 Myr |
| B (HD 73711) | |
| Mass | 2.02[12] M☉ |
| Radius | 2.65[12] R☉ |
| Luminosity | 29[12] L☉ |
| Surface gravity (log g) | 3.90[12] cgs |
| Temperature | 8,236[12] K |
| Metallicity [Fe/H] | +0.79[3] dex |
| Rotational velocity (v sin i) | 56.3[8] km/s |
| Age | 346[13] Myr |
| Other designations | |
| CCDM J08404+1932, WDS J08405+1933 | |
| ε Cancri: Meleph, ε Cnc, 41 Cancri, BD+20°2171, GC 11904, HD 73731, HIP 42556, HR 3429, SAO 98024, GSC 01395-02733 | |
| B: BD+20°2163, GC 11893, HD 73711, SAO 98018 | |
| Database references | |
| SIMBAD | ε Cancri |
| B (HD 73711) | |
The outer 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]
Nomenclature
ε Cancri (Latinised to Epsilon Cancri) is the system's Bayer designation, which originally referred to the entire Beehive Cluster.[17] In his Uranometria, Bayer cited (among others) the name Melleff or Meeleph for the cluster, from Arabic Al Ma'laf, the Stall;[18] as Meleph, this name is also now applied specifically to this star.[19]
In 2016, the IAU organized a Working Group on Star Names (WGSN)[20] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[21] 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]
Properties
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.[22] 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 and so is till on the main sequence.[3]