1995A&A...294..568B

We present the first results from our Crimean-Tuorla programme for polarimetry of distant stars at high galactic latitudes. The available observations reveal a clear increase in the interstellar linear polarization of A and F stars, up to Z≃600pc where one reaches P_V≃0.25%. This means an average A_B≥0.11mag over the northern polar cap for the diffuse component of the interstellar extinction that we are probing. There is no clear indication in the data that the asymptotic level of P_V has been reached, and with future observations above Z=600pc we shall investigate this question. The trend found is in agreement with the stellar reddening analysis by Teerikorpi (1990A&A...235..362T). The directions of the plane of vibration are in agreement with Markkanen's (1979A&A....74..201M) analysis of closer (Z<200pc) stars in his "Area II". Outside of this area we define two sectors B and C which encompass the Local Spiral Arm and had little stars in previous investigations. Here the polarization vectors deviate strongly from those in Markkanen's Area II, where one is probably looking at an interarm region, close to the edge of the Local Spiral Arm. Our measurements indicate for B and C average polarization vectors consistent with the direction l≃110deg obtained by other authors for the magnetic field in the Local Spiral Arm using the rotation measure method.