New Optical Results on gamma-ray Binaries

TL;DR

This paper reports new optical spectroscopic observations of gamma-ray binaries LS 5039 and HESS J0632+067, revealing short-term radial velocity oscillations likely caused by stellar oscillations and long-term emission line variations suggesting orbital modulation.

Contribution

It provides new optical spectroscopic data and analysis of gamma-ray binaries, identifying stable short-term oscillations and long-term emission line variations.

Findings

Sub-orbital radial velocity modulation with ~7 km/s amplitude and ~Porb/4 period.

Stable oscillations over 7 years likely due to stellar non-radial oscillations.

Long-term emission line variations indicating possible orbital periods >200 days.

Abstract

We present new optical spectroscopy of the gamma-ray binary LS 5039. Our data show evidence for sub-orbital modulation in the radial velocities with amplitude ~7 km/s and period ~Porb/4. This short-term oscillation is stable over at least 7 years and it is likely triggered by non-radial oscillations of the O6.5V optical star. We also present the results of a spectroscopic campaign on MWC 148, the optical counterpart of the new gamma-ray binary candidate HESS J0632+067. Long-term variations in the Halpha and Hbeta emission line parameters are clearly detected which, if modulated with the binary orbit, would imply a period >200 days.