(Proposal ID) S15B-122

(PI) Jovanovic, Nemanja

(Proposal Title)
A high angular-resolution study of mass-loss in highly evolved stars

(Abstract)
Mass loss from stars in the last stages of life is the key evolutionary 
wildcard: it governs their ultimate destiny as a supernovae or planetary 
nebulae, and is crucial for galactic chemical enrichment. The mechanisms 
driving the mass loss remain poorly understood; to accelerate a dust-driven 
wind requires grains to form too close to the star, while aspherical and 
clumpy envelopes require an additional mechanism to shape the outflow. 
Multiple models have been proposed, including pulsations, magnetic activity 
and scattering-driven winds. We propose to utilise the unique synergy provided 
by SCExAO by conducting simultaneous observations of northern evolved stars 
using coronagraphic NIR imaging (with HiCIAO) and visible, polarimetric 
interferometry using VAMPIRES. In observations led by the SCExAO and VAMPIRES 
teams, HiCIAO images will reveal the structure - and hence mass-loss history - 
in the mass-loss envelopes of the objects. Simultaneously, VAMPIRES will 
provide diffraction-limited observations of the innermost circumstellar 
regions where the dust formation process takes place, and constrain dust grain 
properties using polarisation. Together, these data will shed light on the 
mystery of the wind driving mechanism and discriminate between competing 
models.