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]
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
SharplessSh2-308, or just S308.[6] It is likely to be a member of the very scattered
open clusterCollinder 121, found around the orange supergiant
ο1 CMa.
^
abcDucati, 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.
^
abSamus, 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.
^
abcdefgSota, 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.
S2CID104292503.