Phase-resolved X-ray and optical spectroscopy of the massive binary HD 93403^*

¹ Institut d'Astrophysique, Université de Liège, Allée du 6 Août, Bât B5c, 4000 Liège (Sart Tilman), Belgium
² School of Physics & Astronomy, University of Birmingham, Edgbaston Birmingham B15 2TT, UK
³ Centre Spatial de Liège, Université de Liège, Avenue du Pré-Aily, 4031 Angleur, Belgium
⁴ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK

Corresponding author: G. Rauw, rauw@astro.ulg.ac.be

Received: 24 July 2001
Accepted: 3 April 2002

Abstract

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD 93403 reveals a clear orbital modulation of the X-ray luminosity as a function of the orbital phase. Below 1.0 keV, the observed X-ray flux is modulated by the opacity of the primary wind. Above 1.0 keV, the observed variation of the X-ray flux is roughly consistent with a dependence expected for an adiabatic colliding wind interaction. HD 93403 appears less overluminuous in X-rays than previously thought and a significant fraction of the total X-ray emission arises probably within the winds of the individual components of the binary. Optical monitoring of the system reveals strong variability of the He ii  λ 4686 and Hα line profiles. The He ii  λ 4686 line displays a broad asymmetrical emission component which is found to be significantly stronger between phases 0.80 and 0.15 than around apastron. This suggests that part of the emission arises in the interaction region and most probably in the trailing arm of a shock cone wrapped around the secondary. Some absorption lines of the secondary's spectrum display equivalent width variations reminiscent of the so-called Struve-Sahade effect. The differences in behaviour between individual lines suggest that the temperature may not be the only relevant parameter that controls this effect.