Imagerie des \'etoiles \'evolu\'ees par interf\'erom\'etrie. R\'earrangement de pupille

TL;DR

This paper demonstrates how single-mode fiber interferometry can be used to produce high-resolution, turbulence-free images of evolved stars, revealing their surface asymmetries and surrounding molecular shells.

Contribution

The authors introduce a novel technique using spatial filtering with single-mode fibers and pupil remapping to reconstruct diffraction-limited images free of speckle noise.

Findings

Achieved high-precision measurements of stellar surface features.

Reconstructed images of stars showing asymmetries and molecular shells.

Simulations suggest over 10^6 dynamic range possible on 8m telescopes.

Abstract

Atmospheric turbulence is an important limit to high angular resolution in astronomy. Interferometry resolved this issue by filtering the incoming light with single-mode fibers. Thanks to this technique, we obtained with the IOTA interferometer very precise measurements of the spatial frequencies of seven evolved stars. From these measurements, we performed a blind deconvolution to restore an image of the surface of the stars. Six of the them, Betelgeuse, Mu Cep, R leo, Mira, Chi Cyg and CH Cyg, feature very asymmetrical brightness distributions. On the other hand, the Arcturus data are extremely well fitted with a simple limb-darkened photospheric disc. From the observations of $\chi$ Cyg, we show that the star is surrounded by a molecular shell undergoing a ballistic motion. We propose to use the same technique of spatial filtering with single-mode fibers to correct for the effect of turbulence in the pupil of a telescope. Because the pupil is redundant, this technique does require a remapping of the pupil. We developed a dedicated algorithm to show that it was possible to reconstruct images at the diffraction limit of the telescope free of any speckle noise. Our simulations show that a high dynamic range (over 10^6) could be obtained in the visible on an 8 meter telescope. A lab experiment is under construction to validate the concept of this new instrument.