  For a continuous map on a topological graph containing a unique loop S it is
possible to define the degree and, for a map of degree 1, rotation numbers. It
is known that the set of rotation numbers of points in S is a compact interval
and for every rational r in this interval there exists a periodic point of
rotation number r. The whole rotation set (i.e. the set of all rotation
numbers) may not be connected and it is not known in general whether it is
closed.
  The graph sigma is the space consisting in an interval attached by one of its
endpoints to a circle. We show that, for a map of degree 1 on the graph sigma,
the rotation set is closed and has finitely many connected components.
Moreover, for all rational numbers r in the rotation set, there exists a
periodic point of rotation number r.
