Observations with the Southern Connecticut Stellar Interferometer. II. First Three-telescope Observations and a New Diameter Measurement of Arcturus

Abstract We discuss the most recent observations made with the Southern Connecticut Stellar Interferometer, which is a three-station stellar intensity interferometer located on the campus of Southern Connecticut State University, in New Haven, Connecticut. Two different kinds of observations are presented. We first analyze observations of Vega taken in a three-telescope mode. (Previously, the instrument had only two operational stations.) We show that, while the efficiency remains nearly identical to that reported in our last paper, the addition of the third station allows more photon data to be recorded simultaneously, and therefore we can build up the photon-bunching peak in the data stream in fewer hours on sky for an unresolved source. In the second part of the paper, we report our observations to date of the nearby red giant star Arcturus, most of which occurred in the first half of 2025. These show that, as a partially resolved source at the baselines we used, we detect fewer correlations in the photon-bunching peak than for an unresolved source of comparable brightness. Combining the data with speckle imaging observations taken at Apache Point Observatory, we derive a new measurement of Arcturus’ diameter that extends the temporal baseline of interferometric observations of the star and is consistent with previous analyses made by other investigators.