Dainis Dravins, Lund's observatory, will hold a seminar entitled "Intensity Interferometry: Sub-milliarcsecond optical imaging with Cherenkov telescope arrays".

Abstract

Much of astronomy is driven by imaging with constantly higher resolution.  The night sky is full of stars but while we observe the light radiated by them, we are still unable - with few exceptions - to observe the stars themselves, i.e., resolve their disks or view structures across and outside their surfaces.  Bright stars have typical sizes of some milliarcsecond(s), and kilometer-scale optical baselines are required for their imaging.  Ordinary phase/amplitude interferometry is hindered by atmospheric turbulence while space interferometry is too complex.  However, atmospheric effects can be circumvented by intensity interferometry, a technique (once pioneered by Hanbury Brown and Twiss in the radio) for measuring the second-order coherence of light.  The required large flux collectors are now becoming available as the arrays primarily erected to measure Cherenkov light emitted in air by particle cascades initiated by energetic gamma rays.  Planned facilities (in particular CTA, Cherenkov Telescope Array) envision many tens of telescopes distributed over a few square km.  Digital signal handling enables very many baselines to be simultaneously synthesized between many pairs of telescopes, while stars may be tracked across the sky with electronic time delays, in effect synthesizing an optical interferometer in software (not unlike LOFAR), enabling two-dimensional imaging with angular resolutions around 30 microarcseconds.