On the periodicities present in the optical light curves of SMC Be/X-ray binaries

TL;DR

This study analyzes optical light curves of SMC Be/X-ray binaries, identifying multiple periodicities and distinguishing their origins, emphasizing careful interpretation of periodic signals in these systems.

Contribution

The paper introduces new metrics to differentiate between mechanisms causing periodicities and categorizes these in a large sample of SMC binaries, advancing understanding of their variability.

Findings

Discovered new optical periodicities in 9 systems.

Identified mechanisms like disk disturbance and pulsations as sources.

Only about 30% of periodicities are clearly linked to orbital periods.

Abstract

We present a comprehensive study of the periodic variations observed in OGLE I-band light curves of SMC Be/X-ray binaries, discovering new optical periodicities in 9 systems. We find that these periodicities derive from a number of mechanisms, notably disturbance of the decretion disk on the orbital period of the system, and aliased non-radial pulsations. We develop metrics that allow these mechanisms to be distinguished on the basis of the shape of the folded optical light curve, and use these metrics to categorise the periodicities present in \sim 50 SMC binary systems. We conclude that extreme care must be taken in the interpretation of the OGLE light curves since only around 30% of the periodicities present can be unambiguously attributed to orbital periods.