ACES Image reconstruction from polarimetric interferometry for probing mass loss from evolved stars
Lucinda Lilley
The University of Sydney, Australia
The VAMPIRES (Visible Aperture Masking Polarimetric Interferometer for Resolving Evolved Stars) instrument of SCExAO/SUBARU combines polarimetry and interferometry to deliver unique observational reach into the astrophysics of the high contrast, immediate stellar environment
of evolved stars. These regions lying within the core of the telescope point spread function are historically difficult to study, but are critical for capturing the physics of mass loss at the circumstellar wind base. Inferring the dynamics in this region will yield answers to many outstanding questions about evolved star mass loss – such as what the physical mechanism launching the wind is, and whether asymmetries in mass loss shells originate at the stellar surface or further out in the envelope.
We are now able to understand and calibrate the instrumental component in our polarimetric observations, disambiguating between instrumental and astrophysical origins for observed ‘phase shifts’ within polarimetric differential visibilities. We have found that VAMPIRES is able to resolve non-azimuthal scattering of dust around red supergiant mu Cephei. This result suggests a complex circumstellar morphology: potentially the presence of resolved polarised asymmetry in the inner mass loss region – significantly closer to the stellar surface than previously thought.
To fit our data, we have employed a combination of classical Bayesian and machine learning methods. Recently we have developed a novel image reconstruction method – which uses a convolutional neural network to perform image reconstruction. Critically, our network simultaneously
reconstructs sub-diffraction limited images which are physically consistent across each reconstructed polarisation state. The enhanced performance of the recently upgraded VAMPIRES, when coupled with our developments to model fitting, highlight the crucial role VAMPIRES is playing in characterising the mass loss physics of evolved stars, with exciting prospects for probing
previously unobservable astrophysics.
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