Polychromatic transfer functions in stellar speckle interferometry

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Abstract
A general expression has been derived for the dichromatic speckle cross spectrum (DCS), using as a unique assumption Korff’s log-normal model for the complex wave amplitude at the telescope pupil. For a given spectral bandwidth, it is shown that the attenuation of the DCS with respect to the monochromatic spectrum is strongly seeing dependent. A high-frequency asymptotic form is derived for the rapid numerical computation of the DCS, thus making it possible to estimate with ease the allowable spectral bandwidth for any given speckle experiment. The performance of the instrumental achromatization technique is analyzed and shown to be useful only with good seeing and narrow bandwidths.