Presentation description

Stellar Intensity Interferometry (SII) enables high-resolution measurements of stellar angular diameters by correlating fluctuations in photon intensity recorded simultaneously at separated telescopes. This technique is well-suited for ground-based observations at optical wavelengths due to its ability to tolerate atmospheric turbulence. In this study, we apply SII to observations of Eta Ursae Majoris (η UMa) using the VERITAS (Very Energetic Radiation Imaging Telescope Array System) array in southern Arizona.
Data was collected by the VERITAS SII system between 2022 and 2025. Correlation functions were extracted and processed with a custom analysis pipeline that includes noise modeling, optical path delay (OPD) corrections, and alignment of correlation peaks across frames. Additional modifications were implemented to account for known electronic delay changes in the array's instrumentation across observing seasons. Each correlation file was manually reviewed, and only those displaying a distinct, sharp correlation peak-indicative of high signal quality-were selected for inclusion in the final analysis. This ensured that only high-quality, high-contrast observations contributed to the angular diameter fit.
After basic analysis, we applied a uniform-disk visibility model to fit the resulting correlation amplitudes as a function of baseline. The analysis produced a well-constrained angular diameter estimate for η UMa. The goodness-of-fit was assessed through chi-squared minimization, which is currently under further refinement.
This work demonstrates the capability of VERITAS to perform precision optical measurements using SII and contributes to the growing body of modern intensity interferometry research. Our results confirm that angular scales in the sub-milliarcsecond regime are accessible with current instrumentation, paving the way for future studies of stellar structure and binarity at high angular resolution.