Speckle Interferometry, Image Reconstruction By Speckle Masking, Speckle Spectroscopy, Multiple-Mirror Interferometry

Abstract

The atmosphere of the earth restricts the resolution of conventional astrophotography to about 1". We will discuss various high-resolution speckle methods which can overcome image degradation caused by the atmosphere and telescope aberrations. All methods yield diffraction-limited resolution, for example 0.03" for a 3.6m telescope. We will show various astronomical applications of speckle interferometry, observations of asteroids, Pluto/Charon, double stars and the gravitational-lens triple quasar. Speckle interferometry can yield a true diffraction-limited image if there is a point source (reference star) in the isoplanatic neighbourhood of the object (holographic speckle interferometry). We show an application of holographic speckle interferometry to the central object R136a of the 30 Doradus nebula in the Large Magellanic Cloud. A true diffraction-limited image of R136a has been reconstructed. The image shows that R136a consists of 8 stars. Speckle masking is a triple correlation method which yields diffraction-limited images of general astronomical objects. A point source near the object is not required. We will describe an application of speckle masking to the central object in the giant H II region NGC 3603. The reconstructed image shows that this central object is a star cluster of 4 stars with magnitudes 11m, 12m, 13m and 13m. The signal-to-noise ratio of the speckle masking image is about the same as the signal-to-noise ratio of the speckle interferometry autocorrelation. Speckle spectroscopy is a speckle method which yields diffraction-limited objective prism spectra. It is also possible to apply speckle masking to multiple-mirror interferometers or long-baseline interferometers on the ground or in space. True images of very high angular resolution can be obtained by these techniques. We will show computer simulations which illustrate the dependence of the signal-to-noise ratio on photon noise.