The impact of dipole straylight contamination on the alignment of low multipoles of CMB anisotropies

We estimate the impact of the dipole straylight contamination (DSC) for the Planck satellite on the alignments of vectors associated with the low multipoles of the pattern of the cosmic microwave background (CMB) anisotropies. In particular we study how the probability distributions of 18 estimators for the alignments change when DSC is taken into account. We find that possible residual DSC should leave a non-negligible impact on low multipole alignments for effective values of the fractional far sidelobe integrated response, p, larger than similar to few x 10(-3). The effect is strongly dependent on the intrinsic sky amplitude and weakly dependent on the considered scanning strategy. We find a decrease of the alignment probability between the quadrupole and the dipole and an increase of the alignment probability between the hexadecapole and the dipole (larger is the intrinsic sky amplitude and lower is the contamination). The remaining estimators do not exhibit clear signatures, except, in some cases, considering the largest values of p and the lowest sky amplitudes. Provided that the real sidelobes of the Planck receivers in flight conditions will correspond to p less than or similar to few x 10(-3), as realistically expected at least in the cosmological frequency channels, and will be known with accuracies better than similar to few x 10 per cent allowing for a suitable cleaning during data reduction, Planck will be very weakly affected from DSC on the alignments of low multipoles.