Circular Polarization Observations at ESO Using UT2 and FORS1

Abstract

We present results from circular polarimetry made by using UT2 and FORS1. In our ESO Programs 076.D-0608A, 076.D-0608B and 077.D-0499A between Dec 12, 2005 and Apr 20, 2006, we have observed a sample of Intermediate Polars (IPs, magnetic cataclysmic variables) by using FORS1 in circular imaging polarimetry mode. The aim of studies were to detect possible polarization effects in Intermediate Polars (IPs) and to search how many of them are polarized and via polarisation data to calculate their magnetic field∈dex magnetic field strengths and to explain accretion behaviour and their evolution.

The measured polarization found in our sample of soft X-ray Intermediate Polars has varied from nearly zero percent up to few percent, and thus high S/N is needed. As the polarization in these objects is due to cyclotron cooling effects near the surface of the white dwarf (WD), and the WD has typically a spin period between 10 and 20 min (in some systems the spin of the WD can be only few minutes) we needed high time resolution to cover rapid circular polarization variations well. These requirements all together emphasize needs of the large telescopes and their light collecting power, such as VLT.