  We present the first linear multicolor polarization observations for a sample
of 35 stars in the direction of the Galactic cluster NGC 6231. We have found a
complex pattern in the angles of the polarimetric vectors. Near the core of
this cluster the structure shows a semi-circular pattern that we have
interpreted as a re-orientation of the dust particles, showing the morphology
of the magnetic field. We propose that a supernova event has occurred some time
ago and produced a shock on the local ISM. We discuss in this paper independent
confirmations othis event, both from the studies on the diffuse interstellar
absorptions Crawford (2001) and the results of the pre-main sequence stars
(PMS) given by Sung et al. (1998). We also show that a supernova is supported
by the evolutive status of the cluster.
