High Spatial Resolution Mid-IR Imaging of V838 Monocerotis: Evidence of New Circumstellar Dust Creation
We report high spatial resolution 11.2 and 18.1 μm imaging of V838 Monocerotis obtained with Gemini Observatory's Michelle instrument in 2007 March. Strong emission is observed from the unresolved stellar core of V838 Mon in our Gemini imagery and is confirmed by Spitzer MIPS 24 μm imaging obtained in 2007 April. The 2007 flux density of the unresolved mid-infrared emission component is ~2 times brighter than that observed in 2004. No clear change in the net amount of 24 μm extended emission is observed between the 2004 and 2007 epoch Spitzer imagery. We interpret these data as evidence that V838 Mon has experienced a new circumstellar dust creation event. We suggest that this newly created dust has condensed from the expanding ejecta produced from V838 Mon's 2002 outburst events and is most likely clumpy. We speculate that one (or more) of these clumps might have passed through the line of sight in late 2006, producing the brief multiwavelength photometric event reported by H. Bond in 2006 and U. Munari et al. in 2007b. We detect no evidence of extended emisssion above a level of ~1 mJy at 11.2 μm and ~7 mJy at 18.1 μm over radial distances of 1860-93,000 AU (0.3''-15.0'') from the central source. Using the simple assumption that ejecta material expands at a constant velocity of 300-500 km s-1, this gap of thermal emission suggests that no significant prior circumstellar dust production events have occurred within the past ~900-1500 yr.