Polarimetric evolution of V838 Monocerotis

We present the results of our polarimetric and spectropolarimetric monitoring of V838 Monocerotis, performed at the Asiago and Crimean observatories during and after the multiple outbursts that occurred in January-March 2002. The polarization of the object is mainly due to interstellar polarization (P\u2dc 2.48%). Intrinsic polarization up to \u2dc 0.7% at 5000 \uc5 is present during the second maximum of the object (February 2002). This intrinsic component increases toward shorter wavelengths but our limited spectral coverage (5000-7500 \uc5) does not allow conclusive inferences about its origin. A strong depolarization across the H\u3b1 profile is observed. The interstellar polarization gives a lower limit to the reddening of E(B-V) >0.28, with E(B-V)\u2dc 0.5 being the most probable value. A normal ratio of total to selective absorption (RV=3.22\ub10.17) was derived from the wavelength of maximum interstellar polarization. This suggests a low (if any) contribution by circumstellar material with a peculiar dust to gas ratio. A polarimetric map of a portion of the light echo shows a complex polarization distribution reaching Pmax=45%. Based on observations collected at Padua Astronomical Observatory at Asiago and Crimean Astrophysical Observatory