Massive binaries as the source of abundance anomalies in globular
  clusters
  Abundance anomalies observed in globular cluster stars indicate pollution
with material processed by hydrogen burning. Two main sources have been
suggested: asymptotic giant branch (AGB) stars and massive stars rotating near
the break-up limit (spin stars). We propose massive binaries as an alternative
source.
  We compute the evolution of a 20 Msun star in a close binary and find that it
sheds about 10 Msun. The ejecta are enriched in He, N, Na, and Al and depleted
in C and O, similar to the abundance patterns observed in gobular cluster
stars. In contrast to the fast, radiatively driven winds of massive stars, this
material is typically ejected with low velocity. We expect that it remains
inside the potential well of a globular cluster and becomes available for the
formation or pollution of a second generation of stars.
  We estimate that the amount of processed low-velocity material ejected by
massive binaries is greater than the contribution of AGB stars and spin stars
combined, assuming that the majority of massive stars in a proto-globular
cluster interact. If we take the possible contribution of intermediate mass
stars in binaries into account and assume that the ejecta are diluted with an
equal amount of unprocessed material, we find that this scenario can provide
enough material to form a second generation of low-mass stars, which is as
numerous as the first generation of low-mass stars. In this scenario there is
no need to make commonly adopted assumptions, such as preferential loss of the
first generation of stars, external pollution of the cluster, or an anomalous
initial mass function. [Abridged]
