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

Niemela, V.S., Gamen, R.C., Barbá, R.H., Fernández Lajús, E., Benaglia, P., Solivella, G.R., Reig, P. and Coe, Malcolm J. (2008) The very massive X-ray bright binary system Wack 2134 (= WR 21a). Monthly Notices of the Royal Astronomical Society, 389 (3), 1447-1452. (doi:10.1111/j.1365-2966.2008.13684.x).

Abstract

From the radial velocities of the N ivλ4058 and He iiλ4686 emission lines, and the N vλ4604-20 absorption lines, determined in digital spectra, we report the discovery that the X-ray bright emission line star Wack 2134 (= WR 21a) is a spectroscopic binary system with an orbital period of 31.673 ± 0.002 d . With this period, the N iv and He ii emission and N v absorption lines, which originate in the atmosphere of the primary component, define a rather eccentric binary orbit (e =  0.64 ± 0.03) . The radial velocity variations of the N v absorptions have a lower amplitude than those of the He ii emission. Such a behaviour of the emission line radial velocities could be due to distortions produced by a superimposed absorption component from the companion. High-resolution echelle spectra observed during the quadrature phases of the binary show H and He ii absorptions of both components with a radial velocity difference of about 541 km s^-1. From this difference, we infer quite high values of the minimum masses, of about 87 and 53 M☉ for the primary and secondary components, respectively, if the radial velocity variations of the He ii emission represent the true orbit of the primary. No He i absorption lines are observed in our spectra. Thus, the secondary component in the Wack 2134 binary system appears to be an early O-type star. From the presence of H, He ii and N v absorptions, and N iv and C iv emissions, in the spectrum of the primary component, it most clearly resembles those of Of/WNLha-type stars.

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Contributors

Author: Malcolm J. Coe

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