  The red giant branch (RGB) of globular clusters (GCs) is home to some exotic
stars, which may provide clues on the formation of multiple stellar populations
in GCs. It is well known that binary interactions are responsible for many
exotic stars. Thus, it is important to understand what fraction of stars on the
RGB of GCs is the result of binary interactions. In this paper, we performed a
binary population synthesis study to track the number of
post-binary-interaction (post-BI) stars that appear on the RGB, with particular
emphasis on the evolved blue straggler stars (E-BSSs). Assuming an initial
binary fraction of nearly 50%, we find that about half of the objects on the
RGB (called giants) underwent the binary interactions, and that E-BSSs account
for around 10% of the giants in our standard simulation. We also compare the
properties of post-BI giants that evolved from different channels. We find that
the initial orbital period and mass ratio distributions significantly affect
the fraction of post-BI giants. Our results imply that the non-standard stars
from binary interactions provide a non-negligible contribution to the RGB stars
in GCs, which should be considered in future investigations of the origin of
multiple stellar populations.
