Asgard/NOTT: L-band nulling interferometry at the VLTI[0.5em] IV. Prospects for characterising hot exozodiacal dust

Abstract

Near-infrared interferometric surveys have revealed extended emission around the photosphere of ≈40 main-sequence stars, attributed to the presence of hot exozodiacal dust (HEZD). A promising technique for investigating this phenomenon is nulling interferometry. The VLTI nulling interferometer NOTT (Nulling Observations of exoplaneTs and dusT) is designed to characterise exoplanets and HEZD in the L′ band (3.5 − 4.0 μm). We aim to assess NOTT’s potential for the detection and characterisation of HEZD with various instrumental and model parameter configurations. We model the HEZD as an optically thin dust ring, using the nearby Sun-like star τ Ceti with HEZD as a reference model. Applying the end-to-end nulling tool SCIFYsim to model the instrumental response of NOTT to simulated HEZD brightness distributions, we evaluate how variations in HEZD and instrumental parameters affect NOTT’s key observables: the photon flux rate and the null depth. We demonstrate that NOTT is capable of disentangling stellar and dust contributions to the signal and detecting HEZD. The null depth and photon flux rate are sensitive to the HEZD geometry, with inclination, position angle, and ring location having the strongest impact on the signal. Although the detailed temporal signatures are target-specific, the results can be generalised to other systems. NOTT has the potential to deliver unprecedented sensitivity for HEZD observations, granting access to detailed information through spectral dispersion, beam-combination schemes, and exploitation of sky rotation. This enables more sensitive HEZD detections than is possible with current instruments, and improved spatial constraints on the dust, as well as variability studies.