Speaker
Description
Recent advances in single-photon detection technology have opened entirely new opportunities for stellar intensity interferometry (SII). In this talk, we present the concept and current development status of SII measurements with the new MAST array. The array consists of twenty 60 cm telescopes, providing a total effective collecting area comparable to that of a single 2.7 m telescope, while requiring only about 10% of the cost.
Each telescope will be equipped with a spectrograph designed to minimize light losses associated with conventional optical filtering. The dispersed light is recorded by a 320-pixel SPAD Lambda detector, providing a spectral resolution of approximately Δλ = 0.2 nm per pixel, allowing to record up to ~80 different spectral lines simultaneously. In this way, we improve for a given observation time the signal-to-noise ratio of the correlation measurements by a factor √80 ≈ 9 with respect to recording only a single spectral line. Combined with the high quantum efficiency and picosecond timing resolution of modern SPAD arrays, we expect an overall SNR 2× higher than the historic Narrabri Intensity Interferometer, despite operating with only ~1% of its collecting area.
A key aspect of the system is the synchronization of different SPAD arrays. For this purpose, we employ a White Rabbit timing system referenced to a GPS antenna, enabling precise time distribution between detector modules. The telescopes, spectrographs, detectors, and synchronization infrastructure are currently being tested in the laboratory.
By demonstrating that small, high-quality telescopes can deliver SII sensitivity on par with—or exceeding—that of large “light-bucket” facilities, we aim to establish a path toward an affordable, dedicated SII observatory with ~50 telescopes and kilometer-scale baselines
forming the next generation of optical SII capability. Two developments are particularly promising in this regard: (i) next-generation SPAD arrays with 10³–10⁴ pixels—already under active development—will enable broader spectral multiplexing, driving order-of-magnitude gains in SNR; (ii) operating multiple telescopes in redundant-baseline or non-redundant configurations will provide, respectively, higher sensitivity and rapid, complete (u,v)-plane coverage. We note that this program is well past the conceptual stage: initial funding has been secured from both national agencies and private sources, the MAST telescopes are being commissioned at the Weizmann Astrophysical Observatory in Israel's Negev desert, and the full SII instrument chain is now undergoing integration toward first on-sky HBT measurements.
