Stellar Coronagraphy Research Articles

The 'Pisco' Speckle Camera at Pic Du Midi Observatory

We present a new speckle camera designed and built at Observatoire Midi-Pyrenees. This focal instrument has been used for four years with the 2-meter Bernard Lyot Telescope of Pic du Midi observatory. It can be set in various operating modes: full pupil imaging, masked-pupil imaging, spectroscopy, wave-front sensor and stellar coronagraphy, hence its name 'PISCO' ('Pupil Interferometry Speckle COronagraph'). Restored images of double and triple stars have demonstrated its capabilities in providing close to diffraction limited images (0.06′′ in V). PISCO has been fully tested and is now ready to be used by the whole astronomical community.

High-resolution ground-based coronagraphy using image-motion compensation

The first results of a new approach to ground-based stellar coronagraphy are reported. A coronagraph has been equipped with an image-motion compensation system for the stabilization of the telescope field, permitting both improved image resolution and contrast at optical wavelengths. By stopping the telescope aperture D to ~ 4 r(0), where r(0) is Fried's parameter, the maximum attainable resolution gain factor of 2.2 was achieved. Gains measured for D/r(0) > 14 were below the theoretical value of 1.3 theory and were indicative of centroid anisoplanatism, a small spatial coherence outer scale, or both. These effects are also evidenced by diminished power at low frequencies in the power spectrum of image motion over the full telescope aperture. A comparison of stabilized and unstabilized images shows that this coronagraph may detect circumstellar objects 2 magnitudes fainter than those detectable with a conventional coronagraph.