V2492 Cygni: The Early Evolution of the 2010 Outburst

Abstract: We present Gemini-North optical and near-IR observations of a young eruptive star in Cygnus, designated as V2492 Cyg in the General Catalog of Variable Stars. This object is one of two young stars, located within 2 degrees of each other, that recently brightened by around 5 mags and were reported as possible new FU Orionis-type variables. The outburst spectrum of V2492 Cyg shows atomic emission features throughout the optical and near-infrared. In the optical, Halpha is in emission and has an associated blue-shifted absorption component. The far-red CaII triplet lines are also in emission and, as with Halpha, possess significant blue-shifted absorption. The optical TiO molecular bands are also in emission. In the near-infrared, Pabeta, Brgamma, and the CO overtone bandheads are strongly in emission. Such spectral characteristics are very similar to those exhibited by both EX Lupi, the progenitor of the EXor class of eruptive variables, during its 2008 extreme outburst, and V1647 Ori during its elevated phase in 2003. Additionally, we consider archival data on V2492 Cyg and investigate the pre-outburst nature of this young star. We construct a quiescent-phase spectral energy distribution which, via model fitting, gives insight into the circumstellar environment of the object prior to the current eruption. Our investigation strongly suggests that the V2492 Cyg outburst appears to be more consistent with an EXor event, a fact supported by its recent 2 mag fading and stochastic variability.