Limitations to null depth S.3. Null depth is limited by the relative spatial extent of the object.
Deep nulls require a high degree of pathlength stability between the two arms of the interferometer.
The amount of variation is a function of the atmospheric parameters and the bandwidth of the interferometer fringe tracker. Note that there will be adequate photon flux from a bright central star for at least a factor of 10 faster fringe tracking than this example, and aggressive tracker algorithms can provide deeper nulls for the same sampling rate. Corrugations in the stellar wavefront caused by imperfect optics reduce the interferometer fringe visibility and hence the null depth. Without further compensation, this limits the null depth S to 0.016. However, it is possible to do significantly better by using a single-mode spatial filter to remove wavefront aberrations.