The Mass-Loss History of the Red Hypergiant VY CMa

TL;DR

This study reconstructs the recent mass-loss history of the red hypergiant VY CMa through imaging and spectroscopy, revealing episodic ejections over the past few centuries linked to stellar variability.

Contribution

It provides detailed measurements of ejecta motions and ages, connecting mass-loss events to stellar activity and variability, highlighting the role of surface activity in red supergiant mass loss.

Findings

Ejecta ages cluster around 70, 120, 200, and 250 years ago.

Recent ejection possibly coincides with a 1985-1995 outburst.

Mass loss is likely driven by surface or convective activity.

Abstract

Imaging and spectroscopy of the knots, clumps, and extended arcs in the complex ejecta of VY CMa confirm a record of high mass loss events over the past few hundred years. HST/STIS spectroscopy of numerous small knots close to the star allow us to measure their radial velocities from the strong K I emission and determine their separate motions, spatial orientations, and time since ejecta. Their ages concentrate around 70, 120, 200 and 250 years ago. A K I emission knot only 50 mas from the star ejected as recently as 1985 -- 1995 may coincide with an H2O maser. Comparison with VY CMa's historic light curve from 1800 to the present, shows several knots with ejection times that correspond with extended periods of variability and deep minima. The similarity of this correspondence in VY CMa with the remarkable recent dimming of Betelgeuse and an outflow of gas is apparent. The evidence for similar outflows from the surface of a more typical red supergiant suggests that discrete ejections are more common and surface or convective activity is a major source of mass loss for red supergiants.