We studied the brightness and spectral evolution of the young eruptive star V1647 Ori during its recent outburst in the period 2004 February – 2006 Sep. We performed a photometric follow–up in the bands V , R _ { \mathrm { C } } , I _ { \mathrm { C } } , J , H , K _ { s } as well as visible and near-IR spectroscopy .
The main results derived from combining our data with those published by other authors are as follows : The brightness of V1647 Ori stayed more than 4 mag above the pre-outburst level until 2005 October when it started a rapid fading .
In the high state we found a periodic component in the optical light curves with a period of 56 days .
The delay between variations of the star and variations in the brightness of clump of nearby nebulosity corresponds to an angle of 61 \arcdeg \pm 14 \arcdeg between the axis of the nebula and the line of sight .
The overall appearance of the infrared and optical spectra did not change in the period March 2004 – March 2005 , though a steady decrease of HI emission line fluxes could be observed .
In 2006 May , in the quiescent phase , the HeI 1.083 \mu m line was observed in emission , contrary to its deep blueshifted absorption observed during the outburst .
The J - H and H - K _ { s } color maps of the infrared nebula reveal an envelope around the star whose largest extension is about 18″ ( 0.03 pc ) .
The color distribution of the infrared nebula suggests reddening of the scattered light inside a thick circumstellar disk .
Comparison of the K _ { s } and H \alpha images of McNeil ’ s Nebula , the conical nebulosity illuminated by V1647 Ori , shows that HH 22A , the Spitzer infrared source and the bright clump C of the nebula may be unrelated objects .
We show that the observed properties of V1647 Ori could be interpreted in the framework of the thermal instability models of Bell et al .
( 1995 ) .
V1647 Ori might belong to a new class of young eruptive stars , defined by relatively short timescales , recurrent outbursts , modest increase in bolometric luminosity and accretion rate , and an evolutionary state earlier than that of typical EXors .