Radial velocities of 329 BHB stars

The observed binary fraction of BHB stars is 18%+/-2% for cases with n>=2 and 21%+/-3% for cases with n>=3, where n represents the number of observation times. After correcting for observational biases, the intrinsic binary fraction increases to 31%+/-3% for n>=2 and 32%+/-3% for n>=3. A clear contrast is observed between halo-like and disk-like BHB stars, with halo-like BHBs exhibiting a lower intrinsic binary fraction (28%+/-3% for n>=2 and 29%+/-3% for n>=3) compared to disk-like BHBs (46%+/-11% and 51%+/-11%, respectively), indicating different formation pathways.

In particular, halo-like BHB stars are more likely to have formed via a single-star evolution channel, whereas disk-like BHB stars may predominantly result from binary evolution processes. Additionally, we find that bluer BHB stars exhibit a significantly higher binary fraction (42%+/-6% for n>=2 and 45%+/-6% for n>=3) than redder BHB stars (24%+/-5% and 23%+/-5%, respectively), which suggests a possible link between binarity and the effective temperature, although more samples are required to confirm this.

No correlation is found between {pi} ({kappa}) and metallicity or kinematics, nor between {pi} ({kappa}) and the effective temperature of BHB stars.