Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. I. The reflection nebula

Aims:The recent outburst of the young eruptive star V1647 Orionis has produced a spectacular appearance of a new reflection nebula in Orion (McNeil's nebula). We present an optical/near infrared investigation of McNeil's nebula. This analysis is aimed at determining the morphology, temporal evolution and nature of the nebula and its connection to the outburst.
Methods: We performed multi epoch B, V, R_C, I_C, z_gunn, and KS imaging of McNeil's nebula and V1647 Ori as well as KS imaging polarimetry. The multiband imaging allows us to reconstruct the extinction map inside the nebula. Through polarimetric observations we attempt to disentangle the emission from the nebula from that of the accretion disk around V1647 Ori. We also attempt to resolve the small spatial scale structure of the illuminating source.
Results: The energy distribution and temporal evolution of McNeil's nebula mimic that of the illuminating source. The extinction map reveals a region of higher extinction in the direction of V1647 Ori. Excluding foreground extinction, the optical extinction due to McNeil's nebula in the direction of V1647 Ori is AV ~ 6.5 mag. The polarimetric measurement shows a compact high polarization emission around V1647 Ori. The percentage of KS band linear polarization goes from 10-20%. The vectors are all well aligned with a position angle of 90° ± 9° East of North. This may correspond to the orientation of a possible accretion disk around V1647 Ori. These findings suggest that the appearance of McNeil's nebula is due to reflection of light by pre-existing material in the surroundings of V1647 Ori. We also report on the discovery of a new candidate brown dwarf or protostar in the vicinity of V1647 Ori as well as the presence of clumpy structure within HH 22A.