The very massive X-ray bright binary system Wack 2134 (= WR 21a)

V.S. NIEMELA; R. C. GAMEN; R. H. BARBÁ; E. FERNÁNDEZ LAJÚS; P. BENAGLIA; G. R. SOLIVELLA; P. REIG; M. J. COE

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

The Royal Astronomical Society, Blackwell Publishing

Año: 2008 vol. 389 p. 1447 - 1452

0035-8711

From the radial velocities of the N IV 4058 and He II 4686 emission lines,and the N V 4604-20 absorption lines, determined in digital spectra, we reportthe discovery that the X-ray bright emission line star Wack 2134 (= WR 21a) isa spectroscopic binary system with an orbital period of 31.673+/-0.002 days.With this period, the N IV and He II emission and N V absorption lines, whichoriginate in the atmosphere of the primary component, define a rather eccentricbinary orbit (e=0.64+/-0.03). The radial velocity variations of the N Vabsorptions have a lower amplitude than those of the He II emission. Such abehaviour of the emission line radial velocities could be due to distortionsproduced by a superimposed absorption component from the companion. Highresolution echelle spectra observed during the quadrature phases of the binaryshow H and He II absorptions of both components with a radial velocitydifference of about 541 km/s. From this difference, we infer quite high valuesof the minimum masses, of about 87Mo and 53Mo for the primary and secondarycomponents, respectively, if the radial velocity variations of the He IIemission represent the true orbit of the primary. No He I absorption lines areobserved in our spectra. Thus, the secondary component in the Wack2134 binarysystem appears to be an early O type star. From the presence of H, He II and NV absorptions, and N IV and C IV emissions, in the spectrum of the primarycomponent, it most clearly resembles those of Of/WNLha type stars.