2023 Fall Meeting of the APS Eastern Great Lakes Section
Friday–Saturday, October 20–21, 2023;
Cleveland State University, Cleveland, Ohio
Session F01: Poster Session
5:30 PM,
Friday, October 20, 2023
Cleveland State University
Room: Fenn Tower 303
Abstract: F01.00037 : Analysis of the ADCs for Stellar Intensity Interferometry
Abstract
Presenter:
John W Scott
(The Ohio State University)
Author:
John W Scott
(The Ohio State University)
In this poster, I will analyze the analog to digital converter (ADC) signal received from each of the four telescopes in VERITAS (the Very Energetic Radiation Imaging Telescope Array system) that we use to provide measurements of the angular diameter of stars. Located in Arizona, the array is primarily used for ultra-high energy gamma ray astronomy. During the full moon when gamma ray astronomy is not possible, the stellar intensity interferometry (SII) group makes use of these telescopes by observing light at a wavelength of 416 nm. The four telescopes provide six pairs with baselines that range from about 35-170m and our observing runs range from 30 minutes to 2 hours. Each of the four telescopes provides its own ADC, which is a measurement of light intensity obtained from photomultiplier tubes (PMTs) on the telescope. The ADC from one telescope is then correlated over the entire length of the run with the ADC from another telescope in the array. The correlation function produced by this process shows a small signal with magnitude on the order of 10e-6 that is known as the “HBT peak”, named after Hanbury Brown and Twiss. The HBT peak is an observed increase in probability of measuring photons from the same source at the same time which, based on this peak and the distance between the telescopes, can be used to give a measurement of the angular diameter of the star. While the individual ADCs do not tell us much about the HBT peak, there is still plenty to learn from an ADC signal before it is correlated with another telescope. By analyzing how the ADCs change as time progresses in the run, we can find characteristics in the signal and detectors and make insights on how they may be affecting our measurements of the stars. One such characteristic is afterpulsing, a type of feedback where the received signal overloads the detector and spreads the signal out over a longer period of time. This can cause uncertainty in the timing of our signal, which is key when correlating it with another ADC to find the HBT peak.