Atmospheric monitoring by star signal analysis using a CMOS camera system for the Telescope Array Project

The Telescope Array (TA) Observatory located in Utah, U.S.A., is dedicated to the study of ultra-high-energy cosmic rays (UHECRs). The project’s primary aim is to investigate the energy spectrum, origin, and composition of these cosmic rays. TA employs a hybrid detection method, using surface detectors (SDs) in combination with fluorescence detectors (FDs). The observation of air showers by FDs provides more direct estimation of the energy of the primary UHECRs, which is used to calibrate the energy estimated by SDs. Atmospheric conditions play an important role in reconstructing the shower parameters. Presently, data acquired by the FDs under cloudy skies is eliminated from the scientific analysis based on the regular visual observations logged by operators in the field. In this work, we aim to additionally assess these atmospheric conditions by monitoring a part of the FD field of view with a wide-angle, high-sensitivity CMOS camera. The analysis results may be compared with the FD data to characterize the variation of the background caused by stars. In this paper, we present this CMOS camera setup and first results toward application to the UHECR observations.