Demonstration of stellar intensity interferometry with the four VERITAS telescopes

Abstract

High angular resolution observations at optical wavelengths provide valuable insights in stellar astrophysics [1, 2], directly measuring fundamental stellar parameters [3, 4], and probing stellar atmospheres, circumstellar disks [5], elongation of rapidly rotating stars [6], and pulsations of Cepheid variable stars [7]. The angular size of most stars are of order one milli-arcsecond or less, and to spatially resolve stellar disks and features at this scale requires an optical interferometer using an array of telescopes with baselines on the order of hundreds of meters. We report on the successful implementation of a stellar intensity interferometry system developed for the four VERITAS imaging atmospheric-Cherenkov telescopes. The system was used to measure the angular diameter of the two sub-mas stars β Canis Majoris and Orionis with a precision better than 5%. The system utilizes an off-line approach where starlight intensity fluctuations recorded at each telescope are correlated post-observation. The technique can be readily scaled onto tens to hundreds of telescopes, providing a capability that has proven technically challenging to current generation optical amplitude interferometry observatories. This work demonstrates the feasibility of performing astrophysical measurements with imaging atmospheric-Cherenkov telescope arrays as intensity interferometers and the promise for integrating an intensity interferometry system within future observatories such as the Cherenkov Telescope Array.

The VERITAS-Stellar Intensity Interferometry (VSII) survey of Stellar Diameters

“…The final visibility curve must be corrected for the presence of night sky background. After this correction, a suitable stellar diameter model is fitted to the visibility curve to extract a reliable measurement of the stellar diameter [7,8]. We will present a sampling of preliminary stellar diameter measurements for selected stars from the VSII survey at the conference.…”

Searching for interstellar quantum communications

“…Photon bunching was observationally shown for sunlight with a result of g (2) (τ ) = 1.45 ± 0.03 (Tan et al 2014), and g (2) (τ ) = 1.7; lower than the expected value of 2 due to noise. The same measurement was successfully performed with starlight (Tan & Kurtsiefer 2017) for stars such as P Cygni with a 1 m telescope, as well as β Canis Majoris and Orioni with the Veritas telescope (Abeysekara et al 2020). In all cases, a significant value for g (2) (τ ) > 1 was found.…”

Intensity interferometry with the MAGIC telescopes

“…From eq. 4 it is clear that intensity interferometry can be realized with large mirror sized telescopes equipped with fast and sensitive electronics, making Imaging Atmospheric Cherenkov Telescopes (IACTs), in particular the 17 meters diameter MAGIC ones, well suited platforms for the implementation of intensity interferometers and the measurement of the diameter of stars [3]. Given the typical distances between IACTs and the typical wavelength it can detect, eq.…”