Multicolor polarization study of Ara OB1

We present the results of a multicolor polarimetric study of stars in the association Ara OB1. Several objects belonging to the clusters NGC 6204, 6193, and 6167 and the local field were observed as part of a global study of the region. The polarimetry shows that the orientation of the polarimetric vectors of each star is very similar within each cluster. The average values are 35 degrees 5 +/- 15 degrees 1 and 52 degrees 2 +/- 16 degrees for NGC 6204 and 6193, respectively. An average value of 106 degrees 5 +/- 9 degrees 9 is found for NGC 6167,but the angle distribution is asymmetric, and a second component can be fitted to the angle histogram (P.A. similar to 120 degrees 8 +/- 11 degrees 6), showing a behavior not observed in NGC 6204 and 6193. So, we suggest that some of the observed stars perhaps belong to another stars grouping, located behind NGC 6167 and between a dust layer with a different orientation of the grains. The large difference in the polarization angle between NGC 6167 and the other two clusters could also be explained because NGC 6167 is supposed to be at the center of a gas-expanding structure and it is possible that this cluster was the origin of the star formation process in the Ara OB1 association, triggered by stellar winds or supernova explosions.