WY Geminorum

WY Geminorum is a binary star system in the northern constellation of Gemini, abbreviated WY Gem. It has an apparent visual magnitude that ranges from 7.26 down to 7.51, which is too faint to be readily viewed with the naked eye. This system is located at a distance of approximately 6,300 light years from the Sun based on parallax measurements, and is receding with a radial velocity of 19.5 km/s.

In 1922, M. L. Humason found the spectrum of HD 42474 matches an M-type star, but with the peculiarity of numerous bright lines. It appears similar to the spectrum of VV Cephei (HR 8383), an eclipsing binary. P. Swings and O. Struve in 1941 discovered emission lines in the ultraviolet spectrum. The presence of a B-type stellar spectrum from a companion star was confirmed by W. P. Bidelman in 1954. The primary spectrum matches an M-type supergiant star. A. Cowley in 1970 found evidence of an atmospheric eclipse of the companion. In 1981, A. Buzzoni determined the primary to be a semi-regular variable of the SRb type with a period of 169 days.

This is a double-lined spectroscopic binary star system with an approximate orbital period of 23550 ± and a high eccentricity (ovalness) of 0.61. The primary component is an M-type supergiant star with a stellar classification of M2Ia or b. The companion is most likely a hotter B-type main-sequence star with a class of B2V. The pair are classified as a VV Cephei-type star system. The companion may be accreting matter from the supergiant around the time of periastron passage, resulting in the formation of an intermittent accretion disk orbiting the hotter star. Radio emission has been detected, which is most likely coming from an ionized region in the stellar wind of the supergiant.