The multiple origin of blue straggler stars

Hagai Perets (Harvard University, USA)
 

Blue straggler stars (BSSs) are stars observed to be hotter and bluer than other stars with the same 
luminosity in their environment. As such they appear to be much younger than the rest of the stellar 
population. BSSs have been identified in various environments, including both open clusters and globular 
clusters as well as in the Galactic halo. Various channels have been suggested for the formation of BSSs, 
including (1) collisions between stars in clusters (2) mass transfer between, or merger of, the components of 
primordial short-period binaries and (3) Induced formation and merger of close inner binaries in triple 
systems due to couple secular evolution and tidal friction. We discuss these formation channels and the 
possible ways to distinguish between them. In particular, we focus on the binarity and higher multiplicity of 
BSSs, and on the orbital properties of binary BSSs. Current observational evidence suggest a combination of 
the formation channels contribute to BSS formation. Halo BSS are likely to have formed through binary stellar 
evolution and cluster BSS were likely to form through all three suggested formation channels.