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EZ Canis Majoris
	Location of EZ CMa (circled)
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Canis Major
Right ascension	06h 54m 13.04410s
Declination	−23° 55′ 42.0150″
Apparent magnitude (V)	6.91 6.71 to 6.95
Characteristics
Spectral type	WN4-s
U−B color index	−0.89
B−V color index	−0.28
Variable type	UGZ?
Astrometry
Proper motion (μ)	RA: −4.431±0.057 mas/yr ; Dec.: 2.884±0.092 mas/yr
Parallax (π)	0.4119 ± 0.0503 mas
Distance	4,900 ly ; (1,500 pc)
Absolute magnitude (MV)	−5.33
Orbit
Period (P)	3.63 d
Semi-major axis (a)	0.13 au
Eccentricity (e)	0.10
Inclination (i)	74°
Details
WR
Mass	23 M☉
Radius	3.25 R☉
Luminosity (bolometric)	620,000 L☉
Temperature	89,100 K
companion
Mass	1.5 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

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]

Binary system

Detail of one edge of the bubble blown by EZ CMa. EZ CMa is off frame to the left (east).

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.^[9] 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.^[9]

A light curve for EZ Canis Majoris, plotted from *TESS* data^[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 H_II 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.

References

^ ^a ^b Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
^ ^a ^b ^c Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
^ ^a ^b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.
^ ^a ^b ^c ^d ^e ^f ^g Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J.; Oskinova, L. M. (2019). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". Astronomy & Astrophysics. A57: 625. arXiv:1904.04687. Bibcode:2019A&A...625A..57H. doi:10.1051/0004-6361/201834850. S2CID 104292503.
^ ^a ^b ^c Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
^ ^a ^b Toalá, J. A.; Guerrero, M. A.; Ramos-Larios, G.; Guzmán, V. (2015). "WISE morphological study of Wolf-Rayet nebulae". Astronomy & Astrophysics. 578: A66. arXiv:1503.06878. Bibcode:2015A&A...578A..66T. doi:10.1051/0004-6361/201525706. ISSN 0004-6361. S2CID 55776698.
^ ^a ^b ^c Schmutz, W.; Koenigsberger, G. (2019). "Long uninterrupted photometric observations of the Wolf-Rayet star EZ CMa by the Toronto BRITE satellite reveal a very fast apsidal motion". Astronomy & Astrophysics. 624: L3. arXiv:1903.09501. Bibcode:2019A&A...624L...3S. doi:10.1051/0004-6361/201935094. S2CID 85459362.
^ Van Der Hucht, Karel A. (2001). "The VIIth catalogue of galactic Wolf–Rayet stars". New Astronomy Reviews. 45 (3): 135–232. Bibcode:2001NewAR..45..135V. doi:10.1016/S1387-6473(00)00112-3.
^ ^a ^b St-Louis, Nicole; Dalton, M. J.; Marchenko, S. V.; Moffat, A. F. J.; Willis, A. J. (1995). "The [ITAL]IUE[/ITAL] Mega Campaign: Wind Structure and Variability of HD 50896 (WN5)". The Astrophysical Journal. 452. Bibcode:1995ApJ...452L..57S. doi:10.1086/309706. S2CID 117990494.
^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.