Intensity interferometry: optical imaging with kilometer baselines

Abstract

Optical imaging with microarcsecond resolution will reveal details across and outside stellar surfaces but requires kilometer-scale interferometers, challenging to realize either on the ground or in space. Intensity interferometry, electronically connecting independent telescopes, has a noise budget that relates to the electronic time resolution, circumventing issues of atmospheric turbulence. Extents up to a few km are becoming realistic with arrays of optical air Cherenkov telescopes (primarily erected for gamma-ray studies), enabling an optical equivalent of radio interferometer arrays. Pioneered by Hanbury Brown and Twiss, digital versions of the technique have now been demonstrated, reconstructing diffraction-limited images from laboratory measurements over hundreds of optical baselines. This review outlines the method from its beginnings, describes current experiments, and sketches prospects for future observations.

Intensity interferometry of P Cygni in the H α emission line: towards distance calibration of LBV supergiant stars

“…LMC versus SMC. The brightest stellar members of Magellanic Clouds have apparent magnitudes in the range of 12 to 15 in the visible and their visibilities could be measured with future extremely long-baseline optical interferometers such as the intensity interferometric mode of the CTA array [10] or connecting large optical telescopes on existing observatories [26], such as Mauna Kea or Paranal, which will offer better than 10 µas angular resolution, compatible with the range of angular di-ameters of the brightest stars of the Magellanic Clouds. Therefore the present work constitutes the first successful step towards settling the quantitative spectroscopy of luminous stars and the W-LR relation, which may serve as an independent calibration technique of cosmological distances comparable to the Cepheid or post-AGB methods [49].…”

“…An extensive review of these experiments is described by Hanbury Brown in his book on the Narrabri interferometer [16], which stopped operating in the early seventies. More recently Cherenkov arrays of telescopes have been considered to revive II with much larger telescopes in size and much longer baselines, aiming at stellar surface imaging by aperture synthesis interferometry on a much broader class of targets [10]. In this context our group started a number of pilot experiments in 2016 using two modest 1 m size optical telescopes.…”

OWL-Moon in 2050 and beyond

“…The issue of the detectability of the mountains has already been addressed for transiting planets [18]. Here we propose a significant improvement, based on the principle of the detection of the silhouette of ringed planets by Intensity Interferometry as developed by Dravins [19]. With a 60 m resolution at the 1.4 pc distance of alpha Cen, for transiting planets, mountains will appear at the border of the planet silhouette during the transit (in case of a transparent atmosphere with no clouds).…”

Enabling discoveries: a review of 30 years of advanced technologies and instrumentation at the National Science Foundation

“…Cerenkov telescopes, which study celestial gamma-ray sources via flashes of light emitted by particle cascades in the upper atmosphere, have the potential for dual-use as optical intensity interferometers. 147 This approach is being pursued with the European Cerenkov Telescope Array. 148 Meanwhile an ATI-funded effort used the Very Energetic Radiation Imaging Telescope Array System, VERITAS, to demonstrate intensity interferometry (1806262/Kieda).…”