One-bit correlator concept for high-resolution speckle imaging: a computer simulation of astronomical observations

摘要

The influence of the atmosphere reduces the angular resolution of long exposures taken with large ground-based telescopes. On the other hand, short exposures contain the complete high-resolution information about the observed object in hidden form. Such short exposures are called speckle interferograms because of their appearance. The hidden object information can be deconvolved from a set of such speckle interferograms by various speckle methods. The speckle masking method can even yield images of the observed object with diffraction-limited resolution. The investigation of the required resolution in dynamic range for the digital recording of the speckle images leads to the simple conclusion: one bit is enough to feasibly detect speckle images for the high- resolution methods. In this article, the applicability of the one-bit detector is investigated in detail. This is done by means of an extensive computer simulation, in which first only a simple object structure - a binary - is used. With the dependence of the image quality obtained by bispectral analysis the useful range of the detection threshold is searched for. In these experiments the following observational parameters are varied: the seeing conditions, the separation and the magnitude difference of the binary. Next, the influence of detector noise and of photon noise is considered. Finally, the simulation of the observation of a NGC 3603-like star cluster is performed. This experiment, in which all disturbing effects are included simultaneously, shows clearly the applicability of the one-bit detector to speckle imaging of more complex objects. The advantages for building and using such a detector motivate the transfer of the concept of one-bit correlation - the correlation of interferometric data detected with a dynamic range of only one bit - from astronomical radio interferometry to speckle observations.