Improving Null Depth Measurement with statistics : theory and first results with the Palomar Fiber Nuller

A unique statistical data analysis method has been developed for reducing nulling interferometry data. The idea is to make use of the statistical distributions of the fluctuating null depths and beam intensities to retrieve the astrophysical null depth in the presence of fluctuations. The approach yields an accuracy much better than is possible with standard data reduction methods, because the accuracy of the null depth is not limited by the sizes of the phase and intensity errors but by the uncertainties on these errors. The result is an improvement in the instrumental null depth measurement limit of roughly an order of magnitude. We show in this paper that broadband null depths of 10-4 can be measured in the lab with our infrared Fiber Nuller without achromatic phase shifters. On sky results are also dramatically improved, with measured contrasts up to 5 x 10-4 with our instrument mounted on the Hale telescope at the Palomar Observatory. This statistical analysis is not specific to our instrument and may be applicable to other interferometers.