Outliers: multicolour photometry guiding the search for evolved binary systems in the globular cluster 47 Tucanae

TL;DR

This study utilizes multicolour photometry from the Hubble Space Telescope to identify and analyze potential evolved binary systems in 47 Tucanae, revealing a new population of likely binary stars through outlier detection.

Contribution

The paper introduces a method using multicolour photometry to identify candidate binary systems in a globular cluster, expanding the understanding of binary populations without relying solely on X-ray detection.

Findings

Identified 24 candidate binary systems as outliers in the colour-magnitude diagram.

Most candidates are likely white dwarf-main sequence binaries without X-ray counterparts.

Some candidates may be double-degenerate systems.

Abstract

We use Hubble Space Telescope multicolour photometry of the globular cluster 47 Tucanae to uncover a population of 24 objects with no previous classification that are outliers from the single-star model tracks in the colour-magnitude diagram and yet are likely cluster members. By comparing those sources with evolutionary models and X-ray source catalogues, we were able to show that the majority of those sources are likely binary systems that do not have any X-ray source detected nearby, most possibly formed by a white dwarf and a main-sequence star and a small number of possible double-degenerate systems.