Astronomy And Astrophysics

. We have carried out deep CCD polarimetry in the I band in selected elds in three lamentary, molecular clouds: the L1400 complex, L204, and MBM25, at galactic latitudes 4 Æ , 21 Æ , and 31 Æ , respectively. I magnitudes and the degree and direction of linear polarization were measured with satisfactory accuracies for 387 stars down to I = 19:5. Typical uncertainties of the degree and angle of polarization are P0.5% and 10 Æ . We also derived extinctions from star counts in and around the observed elds. In the L1400 complex we imaged a 48 arcmin 2 eld in the H and K bands, providing independent measures of extinction based on the E(H K) colour excess. Our measurements show that the patterns of polarization are remarkably smooth over the elds studied, particularly in the L1400 complex. There is no indication of any statistically signicant dierence in polarization angle and degree between obscured and non-obscured regions. MBM25, with the lowest levels of extinctio..