Catalogue of Be/X-ray binary systems in the Small Magellanic Cloud: X-ray, optical & IR properties

TL;DR

This paper compiles a comprehensive catalogue of about 70 Be/X-ray binary systems in the Small Magellanic Cloud, analyzing their multi-wavelength properties, distributions, and correlations to enhance understanding of their characteristics and behaviors.

Contribution

It provides the first combined IR data from Spitzer with ground-based observations and confirms key correlations and bi-modality in the spin period distribution of these systems.

Findings

Bi-modality in spin period distribution is strongly supported.

Correlation between orbital period and disk size is confirmed and quantized.

Homogeneous data set allows re-investigation of previous results.

Abstract

This is a catalogue of approximately 70 X-ray emitting binary systems in the Small Magellanic Cloud (SMC) that contain a Be star as the mass donor in the system and a clear X-ray pulse signature from a neutron star. The systems are generally referred to as Be/Xray binaries. It lists all their known binary characteristics (orbital period, eccentricity), the measured spin period of the compact object, plus the characteristics of the Be star (spectral type, size of the circumstellar disk, evidence for NRP behaviour). For the first time data from the Spitzer Observatory are combined with ground-based data to provide a view of these systems out into the far-IR. Many of the observational parameters are presented as statistical distributions and compared to other similar similar populations (eg isolated Be & B stars) in the SMC, and to other Be/X-ray systems in the Milky Way. In addition previous important results are re-investigated using this excellently homogeneous sample. In particular, the evidence for a bi-modality in the spin period distribution is shown to be even stronger than first proposed, and the correlation between orbital period and circumstellar disk size seen in galactic sources is shown to be clearly present in the SMC systems and quantised for the first time.