The strange hot horizontal-branch binary star in NGC 6752

Abstract

M5865 is the only so-far confirmed close binary found in the extreme horizontal branch (EHB) of a globular cluster. A detailed study has recently proposed that this object could be a close system (period P=1.61 days) comprising a EHB and a main-sequence star of mass M≈0.6 Mʘ. Such a system has never been found among hundreds of known EHB binaries in the field, and it results in a very interesting, unique object. In this contribution, we resume the previous literature results on M5865, we discuss the reasons of interest on it, and we present some very preliminary results obtained from new observations.

Keywords

• close binaries
• horizontal branch
• globular cluster