Interferometric Observations of V838 Monocerotis

We have used long-baseline near-IR interferometry to resolve the peculiar eruptive variable star V838 Mon and to provide the first direct measurement of its angular size. Assuming a uniform disk model for the emission, we derive an apparent angular diameter at the time of observations (2004 November-December) of 1.83 ± 0.06 mas. For a nominal distance of 8 ± 2 kpc, this implies a linear radius of 1570 ± 400 R ☉ . However, the data are somewhat better fitted by elliptical disk or binary component models, and we suggest that the emission may be strongly affected by ejecta from the outburst.