Two decades of optical variability of Small Magellanic Cloud high-mass X-ray binaries

¹ Department of Astronomy, Yale University, PO Box 208101 New Haven, CT 06520-8101, USA
² Department of Physics and Astronomy, Amherst College, C025 New Science Center, 25 East Dr., Amherst, MA 01002-5000, USA
³ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁴ Department of Physics, National and Kapodistrian University of Athens, University Campus Zografos, GR 15784 Athens, Greece
⁵ Institute of Accelerating Systems & Applications, University Campus Zografos, Athens, Greece
⁶ Max-Planck-Institut für Extraterrestrische Physik, Gießenbachstraße 1, D-85748 Garching, Germany
⁷ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

^⋆ Corresponding authors; lena.treiber@princeton.edu, gevas@phys.uoa.gr

Received: 15 June 2024
Accepted: 10 December 2024

Abstract

Aims. We present an analysis of the long-term optical/IR behavior of 111 high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud based on data from the OGLE collaboration.

Methods. Most systems exhibit variability on a range of time scales. This variability regulates the mass transfer to the compact object, while the compact object can, in turn, affect the donor star’s behavior. To better understand this complex interaction and the resulting X-ray properties in these systems, we define a new taxonomy for the observed super-orbital variability.

Results. This taxonomy connects to the color changes, orbital periods, and X-ray behavior of the sources. In most cases, these properties can be explained by differences between the flux of the disk around the Be star and the flux from the star itself. We also refine and present new potential orbital periods and sub-orbital variability in the sources.