The nulling interferometry data standard: NIFITS

The proliferation and scientific impact of optical interferometers in the past 15 years were made possible by the adoption of OIFITS, a standard format for exchanging optical interferometry data. While a few nulling interferometers have been developed and used on sky, their incompatibility with this format has hindered their scientific impact. With this work we aim to construct a data format that can support the exploitation of nulling interferometers. It should be adaptable to all types of nullers, both current and future, and allow data interpretation by teams unfamiliar with the instrument details. This process should not compromise the commitment of nullers to operate at high contrast by rejecting stellar photon noise from the science channels. We offer a standardized way to store the recording of the observation in terms of output flux as directly measured by the system, along with a parametric representation of a forward model of the instrument and its operational state. This is implemented by modeling the beam combination as a complex amplitude transfer matrix linking collected inputs to measured outputs. We show how this can unambiguously describe the instrument transfer function and be used by users agnostic to the instrument in any inference process for astrophysical interpretation.