2009ApJ...699.1015S

We have carried out high-resolution spectroscopic observations of the carbon star V Hya, covering the 4.6 µm band of CO. These data, taken over seven epochs, show that the circumstellar environment of V Hya consists of a complex high-velocity (HV) outflow containing at least six kinematic components with expansion velocities ranging between 70 and 120 km/s, together with a slow-moving normal outflow at about 10 km/s. Physical changes occur in the HV outflow regions on a timescale as short as 2 days, limiting their extent to be ≲10¹⁶ cm. The intrinsic line width for each HV component is quite large (6-8 km/s) compared to the typical values (∼1 km/s) appropriate for normal circumstellar envelopes (CSEs) of asymptotic giant branch stars, due to excess turbulence and/or large velocity gradients resulting from the energetic interaction of the HV outflow with the V Hya CSE. We have modeled the absorption features to set constraints on the temperature distribution in, and the mass ejection rates for gas in the main HV components.