Séminaire de l'INPHYNI: Federico Izraelevitch

The methods used to obtain information about celestial objects from the light reaching our instruments are, at the most basic instrumental level, determining its spatial distribution using an imager and measuring its spectrum. Extensions of these techniques include studying how these observables vary with time, on timescales ranging from minutes to years, as well as measuring the polarization state of the incoming light. Another conceptually different approach relies on interference, which enables observations beyond the diffraction limit of an individual telescope. In classical (amplitude) interferometry, the optical fields collected by two separated telescopes are combined coherently and detected together. In quantum (intensity) interferometry, the photon arrival times are recorded independently at two separated telescopes, and the second-order correlation function is computed.

IC4Stars (Intensity Correlations for Stars) is a project that aims to directly measure the physical size of a white dwarf star for the first time using intensity interferometry (also known as the Hanbury-Brown and Twiss effect). The experiment measures photon arrival times independently at distant astronomical telescopes, using a common time base synchronized to picosecond precision. In this talk, we will review the efforts of the Nice team in this field over the past few years and the current status of the project. We will present the results of an on-sky observation campaign conducted at the Calern site of the Observatoire de la Côte d’Azur in April 2026, as well as our plans to deploy a setup at Mauna Kea Observatory, Hawaii, in early 2027. We will explain why measuring just one star can provide valuable insight into the final evolutionary stage of the vast majority of stars in our Universe. We will also discuss how the Pauli exclusion principle gives rise to a macroscopic effect that determines their ultimate fate.