Sculpting an AGB Mass-Loss Envelope into a Bipolar Planetary Nebula: High-Velocity Outflows in V Hydrae

TL;DR

This study uses high-resolution spectroscopy to analyze the complex high-velocity outflows in the circumstellar environment of the carbon star V Hya, revealing multiple kinematic components and rapid physical changes.

Contribution

It provides detailed characterization of V Hya's high-velocity outflows, including their velocities, turbulence, and interaction with the circumstellar envelope, advancing understanding of planetary nebula formation.

Findings

Multiple high-velocity components with velocities 70-120 km/s identified.

Rapid physical changes in outflows occur on timescales as short as two days.

Large line-widths indicate significant turbulence or velocity gradients.

Abstract

We have carried out high-resolution spectroscopic observations of the carbon star V Hya, covering the 4.6 micron band of CO. These data, taken over 7 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 time-scale as short as two days, limiting their extent to < ~ 10^{16} 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 AGB circumstellar envelopes (CSEs), 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 modelled the absorption features to set constraints on the temperature distribution in, and the mass ejection-rates for gas in the main HV components.