Performance of the Gemini Planet Imager's adaptive optics system.

The Gemini Planet Imager's adaptive optics (AO) subsystem was designed specifically to facilitate high-contrast imaging. A definitive description of the system's algorithms and technologies as built is given. 564 AO telemetry measurements from the Gemini Planet Imager Exoplanet Survey campaign are analyzed.

First light of the Gemini Planet imager.

The Gemini Planet Imager is a dedicated facility for directly imaging and spectroscopically characterizing extrasolar planets. It combines a very high-order adaptive optics system, a diffraction-suppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution. Every aspect of the Gemini Planet Imager has been tuned for maximum sensitivity to faint planets near bright stars.

Dating of sediment record at two contrasting sites of the Seine River using radioactivity data and hydrological time series.

Sediment cores were collected at the outlet of the highly anthropogenized catchment of the Seine River at two contrasting sites: a flood plain of the lower Seine River and a quasi-permanently submerged harbour basin (or wet dock) in the upper tidal estuary. Analyses of artificial radionuclides ((137)Cs and plutonium isotopes), coupled with hydrological and bathymetric data, lead to a precise dating of the sediment cores collected at the two sites. (137)Cs signals originating from global fallout (early 1960s) and from the Chernobyl accident (1986) are identified, but at different levels due to the incomplete nature or variable continuity of the records.

Computer vision applications for coronagraphic optical alignment and image processing.

Modern coronagraphic systems require very precise alignment between optical components and can benefit greatly from automated image processing. We discuss three techniques commonly employed in the fields of computer vision and image analysis as applied to the Gemini Planet Imager, a new facility instrument for the Gemini South Observatory. We describe how feature extraction and clustering methods can be used to aid in automated system alignment tasks, and also present a search algorithm for finding regular features in science images used for calibration and data processing.

Production of phase screens for simulation of atmospheric turbulence.

The ability to simulate atmospheric turbulence in the laboratory is a crucial part of testing and developing astronomical adaptive optics (AO) technology. We report on the development of a technique for creating phase plates that involves the strategic application of clear acrylic paint onto a transparent substrate. Results of interferometric characterization of these plates are described and compared to Kolmogorov statistics.

Analysis of on-sky sodium profile data from Lick Observatory.

The next generation of adaptive optics will depend on laser guide stars to increase sky coverage. However, there are a few limitations. The thickness of the sodium layer in the mesosphere at 90 km causes spot elongation, which is more severe for large telescopes.

Amplitude variations on a MEMS-based extreme adaptive optics coronagraph testbed.

High-contrast imaging techniques such as coronagraphy are expected to play an important role in the imaging of extrasolar planets. Instruments like the Gemini Planet Imager (GPI) or the Spectro-Polar-Imetric High-Contrast Exoplanet Research (SPHERE) require high-dynamic range, achieved using coronagraphs to block light coming from the parent star. An extremely good adaptive optics (AO) system is required to reduce dynamic atmospheric wavefront errors to 50-100 nm rms.

Laboratory demonstration of accurate and efficient nanometer-level wavefront control for extreme adaptive optics.

A 32 x 32 microelectricalmechanical systems mirror is controlled in a closed-loop adaptive optics test bed with a spatially filtered wavefront sensor (WFS), Fourier transform wavefront reconstruction, and calibration of references with a high-precision interferometer. When correcting the inherent aberration of the mirror, 0.7 nm rms phase error in the controllable band is achieved.