Imaging stellar surfaces with intensity interferometry

Sammanfattning: Context. Intensity interferometry was invented and used by R.Hanbury Brown and R.Q.Twiss in the 1960's to measure stellar angular diameters. Its main advantage over conventional interferometry is that it enables very long baselines and is insensitive to poor seeing. However, because it requires very large light collectors, it was never pursued further. The Cherenkov Telescope Array (CTA) is a new upcoming facility that will detect rapid flashes of optical Cherenkov light induced by extraterrestrial gamma-rays. Its large telescopes could very well be used part-time for intensity interferometry. With its 2 km maximum baseline, it could image surfaces of hot stars at an unprecedented sub-milliarcsecond resolution. Aim. To experimentally simulate intensity interferometry in the laboratory with an array analogous to the planned CTA. Methods. Small pinhole apertures were illuminated by experimentally produced light with appropriate quantum statistics to simulate stars. High-speed single-photon counting avalanche diode detectors mounted on laboratory telescopes made up the array, enabling more than 100 baselines. A digital data processor was used to calculate the spatial coherence of the stars. Results. Intensity interferometry was successfully performed for stars of different sizes and shapes. With all the baselines available, it was possible to reconstruct two-dimensional maps of the spatial coherence required for image restoration. Conclusions. The results experimentally demonstrated the validity and potential of a multi-telescope array similar to the CTA for stellar surface imaging.