BHB and MS in inner Galactic halo

They are, hence, very old objects that can be used as markers in studying galactic structure and formation history. Their formation requires significant mass loss during the red-giant phase, but the role of stellar interactions in this process remains unclear.

Knowing the fraction of BHBs that exist in binary or higher multiple systems where mass transfer may occur will enhance our understanding of their stellar evolution. We determine the fraction of BHBs in binary systems over a wide range of separations in the inner Galactic Halo to constrain mass-loss mechanisms and evolutionary pathways. Using a catalogue of 22336 BHB candidates from Gaia DR3, we analysed radial velocity variations found in spectra (263 spectra of 89 targets) acquired using the Ondvrejov Echelle spectrograph attached to the Perek 2m telescope at the Astronomical Institute of the Czech Academy of Sciences together with archival spectra from the Ultraviolet and Visual Echelle Spectrograph (UVES) and Fiber-fed Extended Range Optical Spectrograph (FEROS).