2002ApJ...567L.137M

The eccentric W-R + O binary system WR 140 produces dust for a few months at intervals of 7.94 yr coincident with periastron passage. We present the first resolved images of this dust shell, at binary phases φ∼0.039 and ∼0.055, using aperture masking techniques on the Keck I telescope to achieve diffraction-limited resolution. Proper motions of approximately 1.1 mas per day were detected, implying a distance ≲1.5 kpc from the known wind speed. The dust plume observed is not as simple as the ``pinwheel'' nebulae seen around other W-R colliding wind binaries, indicating the orbital plane is highly inclined to our line of sight and/or the dust formation is very clumpy. Follow-up imaging in the mid-infrared and with adaptive optics is urgently required to track the dust motion further, necessary for unambiguously determining the orbital geometry, which we only partially constrain here. With full knowledge of the orbital elements, these infrared images can be used to reconstruct the dust distribution along the colliding wind interface, providing a unique tool for probing the postshock physical conditions of violent astrophysical flows.