The Highly Polarized Open Cluster Trumpler 27

We have carried out multicolor linear polarimetry (UBVRI) of the brighteststars in the area of the open cluster Trumpler 27. Our data show a high levelof polarization in the stellar light with a considerable dispersion, from $P =4%$ to $P = 9.5%$. The polarization vectors of the cluster members appear to bealigned. Foreground polarization was estimated from the data of some non-memberobjects, for which two different components were resolved: the first oneassociated with a dust cloud close to the Sun producing $P_{\lambda max}=1.3%$and $\theta=146$ degrees, and a second component, the main source ofpolarization for the cluster members, originated in another dust cloud, whichpolarizes the light in the direction of $\theta= 29.5$ degrees. From a detailedanalysis, we found that the two components have associated values $E_{B-V} <0.45 $ for the first one, and $E_{B-V} > 0.75$ for the other. Due thedifference in the orientation of both polarization vectors, almost 90 degrees(180 degrees at the Stokes representation), the first cloud ($\theta \sim 146$degrees) depolarize the light strongly polarized by the second one ($\theta\sim 29.5$ degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in A