EZ Canis Majoris
Binary star system in the constellation Canis Major
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EZ Canis Majoris (abbreviated to EZ CMa, also designated as WR 6) is binary system in the constellation of Canis Major. The primary is a Wolf-Rayet star and it is one of the ten brightest Wolf-Rayet stars, brighter than apparent magnitude 7.[8]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Canis Major |
| Right ascension | 06h 54m 13.04410s[1] |
| Declination | −23° 55′ 42.0150″[1] |
| Apparent magnitude (V) | 6.91[2] 6.71 to 6.95[3] |
| Characteristics | |
| Spectral type | WN4-s[4] |
| U−B color index | −0.89[2] |
| B−V color index | −0.28[2] |
| Variable type | UGZ?[3] |
| Astrometry | |
| Proper motion (μ) | RA: −4.431±0.057[5] mas/yr Dec.: 2.884±0.092[5] mas/yr |
| Parallax (π) | 0.4119±0.0503 mas[5] |
| Distance | 4,900 ly (1,500[6] pc) |
| Absolute magnitude (MV) | −5.33[4] |
| Orbit[7] | |
| Period (P) | 3.63 d |
| Semi-major axis (a) | 0.13 au |
| Eccentricity (e) | 0.10 |
| Inclination (i) | 74° |
| Details | |
| WR | |
| Mass | 23[4] M☉ |
| Radius | 3.25[4] R☉ |
| Luminosity (bolometric) | 620,000[4] L☉ |
| Temperature | 89,100[4] K |
| companion | |
| Mass | 1.5[7] M☉ |
| Other designations | |
| EZ CMa, ALS 98, CD−23°4553, CEL 1426, Collinder 121 4, CPD−23°1588, GC 9061, HD 50896, Hen 3-20, HIP 33165, HR 2583, LBN 1052, MR 6, PPM 251223, SAO 172546, SH 2-308, TYC 6522-3270-1, WR 6 | |
| Database references | |
| SIMBAD | data |
Binary system
L. W. Ross announced his discovery that the star's brightness varies, in 1961.[9] EZ CMa has an apparent visual magnitude which varies between 6.71 and 6.95 over a period of 3.766 days, along with changes in the spectrum.[10] It has been proposed that it could be a binary star, with a neutron star as companion that would complete an orbit around the Wolf-Rayet with that period, being the cause of those variations. The General Catalogue of Variable Stars lists it as a possible cataclysmic variable on this basis. It has been argued that the companion does not exist and spectral variations are caused by activity on the star's surface.[10]
Observations of the light variations over a four-month period from late 2015 to early 2016 confirmed the clear 3.76 d variations. This was interpreted as a 3.66 d orbital period with rapid apsidal precession completing a full rotation in about 100 days. The orbit is inclined at around 60–74 degrees and there are two eclipses during each orbit.[7]
Wolf Rayet star and nebula
The spectral type of WN4 indicates an extremely hot star, and this leads to a very high luminosity, mostly emitted as ultraviolet radiation. The spectrum shows a star entirely devoid of hydrogen at the surface.[4]
EZ CMa is surrounded by a faint bubble nebula, a small HII region blown by stellar winds up to 1,700 km/s and ionised by the intense UV radiation. This is catalogued as Sharpless Sh2-308, or just S308.[6] It is likely to be a member of the very scattered open cluster Collinder 121, found around the orange supergiant ο1 CMa.