Abstract
Abstract We discuss the design, construction, and operation of a new intensity interferometer, based on the campus of Southern Connecticut State University in New Haven, Connecticut. While this paper will focus on observations taken with an original two-telescope configuration, the current instrumentation consists of three portable 0.6 m Dobsonian telescopes with single-photon avalanche diode detectors located at the Newtonian focus of each telescope. Photons detected at each station are time stamped and read out with timing correlators that can give cross-correlations in timing to a precision of 48 ps. We detail our observations to date with the system, which has now been successfully used at our university in 16 nights of observing. Components of the instrument were also deployed on one occasion at Lowell Observatory, where the Perkins and Hall telescopes were made to function as an intensity interferometer. We characterize the performance of the instrument in detail. In total, the observations indicate the detection of a correlation peak at the level of 6.76σ when observing unresolved stars, and consistency with partial or no detection when observing at a baseline sufficient to resolve the star. Using these measurements, we conclude that the angular diameter of Arcturus is larger than 15 mas and that of Vega is between 0.8 and 17 mas. While the uncertainties are large at this point, both results are consistent with measures from amplitude-based long baseline optical interferometers.
Highlights
Intensity interferometry, first proposed by Hanbury Brown & Twiss (1956, 1958), can be used as a method of extracting very high resolution information of astrophysical sources based on the super-Gaussian statistics of photons, referred to as the Hanbury Brown and Twiss (HBT) effect
While this paper will focus on observations taken with an original two-telescope configuration, the current instrumentation consists of three portable 0.6-m Dobsonian telescopes with single-photon avalanche diode (SPAD) detectors located at the Newtonian focus of each telescope
The signal-to-noise ratios (SNRs) is a linear function of the square root of the number of correlations seen in a typical timing bin in the final cross-correlation function for an observing session, where the slope is the fraction of correlated photons
Summary
First proposed by Hanbury Brown & Twiss (1956, 1958), can be used as a method of extracting very high resolution information of astrophysical sources based on the super-Gaussian statistics of photons, referred to as the Hanbury Brown and Twiss (HBT) effect They showed that light recorded by two independent detectors at different locations has a weak correlation in intensity if the object being viewed was indistinguishable from a point source. Over the last several years, our group has designed, built, and operated a new intensity interferometer based mainly at the campus of Southern Connecticut State University, but which is modular enough to transport the photon-detection instrumentation to other astronomical facilities (Horch & Camarata 2012; Horch et al 2016, 2018; Weiss, Rupert, & Horch 2018; Klaucke et al 2020) It belongs to the second category of intensity interferometers just mentioned in that it uses 0.6-m telescopes and SPAD detectors. We use the correlations detected to make deductions concerning the diameters of Vega (α Lyr, HR 7001), and Arcturus (α Boo, HR 5340); while still uncertain, these measurements are consistent with those made with the larger Michelson-style optical interferometers
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