WR 137 is a

variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...

Wolf-Rayet star located around 6,000 light years away from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

in the constellation of Cygnus. WR 137, together with

WR 134 WR 134 is a variable Wolf-Rayet star located around 6,000 light years away from Earth in the constellation of Cygnus, surrounded by a faint bubble nebula blown by the intense radiation and fast wind from the star. It is five times the ...

and

WR 135 WR 135 is a variable Wolf-Rayet star located around 6,000 light years away from Earth in the constellation of Cygnus, surrounded by a faint bubble nebula blown by the intense radiation and fast wind from the star. It is just over four ti ...

, was one of three stars in Cygnus observed in 1867 to have unusual spectra consisting of intense

emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s rather than the more normal continuum and

absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s. These were the first members of the class of stars that came to be called Wolf-Rayet stars (WR stars) after Charles Wolf and

Georges Rayet Georges-Antoine-Pons Rayet (12 December 1839 – 14 June 1906) was a French astronomer. He was born in Bordeaux, France. He began working at the Paris Observatory in 1863. He worked on meteorology in addition to astronomy. He specialized ...

who discovered their unusual appearance. It is a member of the carbon sequence of WR stars, indicated by the lack of nitrogen lines and the strength of carbon emission. WR 137 has a spectrum with C_III emission weaker than C_IV and O_V weaker still, leading to the assignment of a WC7 spectral type. The spectrum also shows emission lines of He_II and O_IV. V1679CygLightCurve

WR 137 is a binary system, with an O9 main sequence or giant companion. The two stars orbit every thirteen years in a mildly eccentric orbit, and there is an episode of dust production near

periastron An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...

. The inclination of the orbit is uncertain, most likely near 67° but with some analyses suggesting values around 23°. The O star is visually brighter and more massive, but the WR star dominates the spectrum and has a higher bolometric luminosity. Visible in the spectrum are

s and some narrow emission lines, each thought to originate from the secondary star. The line profiles suggest a

decretion disc Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

around the star, produced by its rapid rotation, which would make it the only known system containing a WR star and an Oe star. WR 137 is about a degree away from WR 135 and the two are believed to lie at approximately the same distance from Earth within the Cygnus OB3 association. Its properties are uncertain because of the presence of the hot luminous companion. A pseudo-fit of the combined spectrum yielded a temperature of 56,000 K, a luminosity of , and a radius of . A more typical radius for a WC7 star would be , implying a hotter temperature.

Evolutionary Evolution is change in the heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes, which are passed on from parent to ...

modelling of the WR 137 pair suggest an initial mass for the primary of and for the secondary of , with an age of 4.1 million years. The initial orbital period would have been around 1,580 days. Around have been transferred from the primary to the secondary.

References

External links

Wolf-Rayet shells
showing a spectrum of WR 135
WR134 Ring Nebula
with WR 135 visible in the top left corner {{Stars of Cygnus Cygnus (constellation) Wolf–Rayet stars Cygni, V1679 099769 192641 Durchmusterung objects Spectroscopic binaries O-type main-sequence stars