The Struve-Sahade effect in the optical spectra of O-type binaries I. Main-sequence systems

TL;DR

This study investigates the Struve-Sahade effect in four O-type binary systems using high-resolution spectra, revealing that the effect influences both stars' spectra and varies with the system's orbital phase and characteristics.

Contribution

It provides new orbital solutions and spectral types for four massive binaries and demonstrates that the Struve-Sahade effect impacts both components differently depending on the system.

Findings

Equivalent width variations occur during orbital cycles.

The effect influences both primary and secondary spectra.

Some variations are linked to the systems' ellipsoidal variability.

Abstract

We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the Struve-Sahade effect (defined as the apparent strengthening of the secondary spectrum of the binary when the star is approaching, and the corresponding weakening of the lines when it is receding). We use high resolution optical spectra to determine new orbital solutions and spectral types of HD 165052, HD 100213, HD 159176 and DH Cep. As good knowledge of the fundamental parameters of the considered systems is necessary to examine the Struve-Sahade effect. We then study equivalent width variations in the lines of both components of these binaries during their orbital cycle. In the case of these four systems, variations appear in the equivalent widths of some lines during the orbital cycle, but the definition given above can any longer be valid, since it is now clear that the effect modifies the primary spectrum as much as the secondary spectrum. Furthermore, the lines affected, and the way in which they are affected, depend on the considered system. For at least two of them (HD 100213 and HD 159176) these variations probably reflect the ellipsoidal variable nature of the system.