Pointing calibration of LHAASO-WFCTA telescopes using bright stars

One of the main scientific objectives of the Large High Altitude Air Shower Observatory (LHAASO) is to perform accurate measurements of the energy spectra for different cosmic ray masses, from a few TeV to 100 PeV. As one of the main sub-arrays of LHAASO, the Wide Field-of-View Cherenkov Telescope Array (WFCTA), which consists of 18 telescopes, can help in achieving this goal. The pointing accuracy of each telescope is crucial for reconstructing energy and determining mass-sensitive parameters. In this study, a method for absolute pointing calibration using ultraviolet bright stars was established. The proposed method can achieve a pointing accuracy of approximately 0.02 degrees by using more than five stars. When more stars are used in the telescope's field of view, the accuracy of the pointing calibration can be improved, e.g, a pointing accuracy of 0.01 degrees can be achieved when using more than 15 stars. A high-precision inclinometer with a monitor resolution of 0.003 degrees was installed on the camera to monitor the zenith direction of the telescope at every second. After calibration using bright stars, the absolute pointing accuracy of the inclinometer was 0.02 degrees.

Automated summary

The Large High Altitude Air Shower Observatory (LHAASO) aims to accurately measure the energy spectra for different cosmic ray masses. The Wide Field-of-View Cherenkov Telescope Array (WFCTA), as one of its main sub-arrays, plays a crucial role in achieving this goal. This study established a method for absolute pointing calibration using ultraviolet bright stars, which can achieve high pointing accuracy.