WR 137, together withWR 134 andWR 135, was one of three stars inCygnus observed in 1867 to have unusual spectra consisting of intenseemission lines rather than the more normal continuum andabsorption lines. These were the first members of the class of stars that came to be called Wolf-Rayet stars (WR stars) afterCharles Wolf andGeorges Rayet who discovered their unusual appearance.[12] 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 CIII emission weaker than CIV and OV weaker still, leading to the assignment of a WC7 spectral type. The spectrum also shows emission lines of HeII and OIV.[13][14]
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 nearperiastron. The inclination of the orbit is high, near 97 degrees.[10] 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 areabsorption lines and some narrow emission lines, each thought to originate from the secondary star. The line profiles suggest adecretion disc around the star, produced by its rapid rotation, which would make it the only known system containing a WR star and anOe star.[11]
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.[15] 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 537,000 L☉, and a radius of 10 R☉. A more typical radius for a WC7 star would be 4.5 R☉, implying a hotter temperature.[9]
Evolutionary modelling of the WR 137 pair suggest an initial mass for the primary of 60 M☉ and for the secondary of 30 M☉, with an age of 4.1 million years. The initial orbital period would have been around 1,580 days. Around three M☉ have been transferred from the primary to the secondary.[11]
Observations withJWST instrument MIRI did resolve 10 rings around the binary, representing 131 years of dust ejection. The dust moves with a speed of 1700 km/s, near theterminal velocity. Each ring represents a dust plume, which starts to form near aquadrature in their orbit and continues after theconjunction. This results in dust being seen in both directions along the nearly edge-on orbital plane.[1]
^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.Bibcode:2002yCat.2237....0D.
^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.Bibcode:2009yCat....102025S.
