WR 140
WR 140 is a visually moderately bright Wolf-Rayet star placed within the spectroscopic binary star, SBC9 1232, whose primary star is an evolved spectral class O4-5 star. It is located in the constellation of Cygnus, lying in the sky at the centre of the triangle formed by Deneb, γ Cygni and δ Cygni. WR 140 has been described as the brightest Wolf Rayet star in the northern hemisphere, although WR 133 also in Cygnus is comparably bright. The Wolf-Rayet component is identified as the secondary star, being less massive, less luminous, and probably less visually  bright than its primary even though it dominates the spectrum with its broad emission lines. The primary star is an O4-5 star, most likely a giant or supergiant. Its current accepted spectroscopic orbit is highly eccentric and has an orbital period of 7.9 ± 0.2 years, which has been determined from the velocity variations observed with the component's spectral lines, mostly from the Balmer absorption lines of the O4-5 primary and C IV emission lines at 465.0 nm for WR 140. Separation between these two stars varies from 1.3 AU at periastron to 23.9 AU at apastron . WR 140 is listed as a Wolf-Rayet variable star, and has been given the variable star designation V1687 Cyg in the General Catalogue of Variable Stars, whose visual brightness varies only very slightly. Interest with this WR 140 system is principally observing the infrared light fluctuations during the component's orbit, being extensively studied because of its episodic dust formation. It is now regarded as the prototype colliding-wind binary. Shortly after periastron passage every eight years, the infrared brightness increases dramatically and then slowly drops again over a period of months. Here stellar winds collide with the dust  formation created by the stars.