Scintillation correction on the VLT using tomographic wavefront sensing

ABSTRACT The development of adaptive optics (AO) to correct the effects of optical turbulence has made ground-based telescopes increasingly competitive with those in space. However, AO cannot correct for atmospheric scintillation noise, which severely limits the precision of time-resolved photometry for ground-based observations of bright targets such as exoplanet transits. A scintillation correction technique has been proposed and tested on-sky that uses tomographic wavefront sensing and turbulence profile measurements to produce an estimate of the intensity fluctuation due to scintillation. These estimated scintillation patterns can then be used to correct the photometric data. A key benefit of this technique is that it can easily be applied to most existing tomographic AO systems without any additional hardware, and can also be performed entirely in post-processing. Previously, a simple proof-of-concept experiment to demonstrate the technique was performed and published, observing the Orion Trapezium asterism as reference stars for the wavefront sensing on the Isaac Newton Telescope. However, the scintillation correction technique is ideally suited to much larger telescopes with laser guide stars, which allows a far greater sky coverage. We present a demonstration of this scintillation correction technique using data from the GALACSI (Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging) instrument on the Adaptive Optics Facility at the Very Large Telescope (VLT). On average, the scintillation index was reduced by a factor of $2.7 \pm 0.2$. This will enable higher precision exoplanet transit analysis, and hence detections of smaller planets, from the ground.