V1647 Orionis (IRAS 05436−0007) in Outburst: The First Three Months

We report on photometric (BVRIJHK) and low-dispersion spectroscopic observations of V1647 Orionis, the star that drives McNeil's Nebula, between 2004 February 10 and May 7. The star is photometrically variable atop a general decline in brightness of about 0.3–0.4 mag during these 87 days. The spectra are featureless, aside from Hα and the Ca II infrared triplet in emission and a Na II D absorption feature. The Ca II triplet line ratios are typical of young stellar objects. The Hα equivalent width may be modulated on a period of about 60 days. The postoutburst extinction appears to be less than 7 mag. The data are suggestive of an FU Orionis–like event, but further monitoring will be needed to definitively characterize the outburst.