Monitoring the pointing of the prototype LST-1 using star reconstruction in the Cherenkov camera

TL;DR

This paper presents a star reconstruction method for real-time monitoring of the LST-1 telescope's pointing accuracy during sky observations, complementing existing calibration techniques and enhancing performance verification.

Contribution

It introduces a novel star-based pointing monitoring approach that operates during normal data acquisition without additional hardware or dedicated observations.

Findings

Method successfully reconstructs star positions in simulated data.

Provides real-time validation of telescope pointing accuracy.

Complementary to existing CCD camera calibration methods.

Abstract

The first Large-Sized Telescope (LST-1) proposed for the forthcoming Cherenkov Telescope Array (CTA) has started to operate in 2019 in La Palma. The large structure of LST-1 - with a 23 m mirror dish diameter - imposes a strict control of its deformations that could affect the pointing accuracy and its overall performance. According to CTA specifications that are conceived to resolve e.g. the fine structure of galactic sources, the LST post-calibration pointing accuracy should be better than 14 arcseconds. To fulfill this requirement, the telescope pointing precision is monitored with two dedicated CCD cameras located at the dish center. The analysis of their images allows us to disentangle different systematic deformations of the structure. In this work, we investigate a complementary approach that offers the possibility to monitor the pointing of the telescope during the acquisition of sky data. After properly cleaning the events from the Cherenkov showers, the reconstructed positions of the stars imaged in the camera field of view are compared to their nominal expected positions in catalogues. This provides a direct measurement of the telescope pointing, that can be used to cross-check the other methods and as a real-time monitoring of the optical properties of the telescope and of the pointing corrections applied by the bending models. Additionally, this method benefits from not relying on specific hardware or dedicated observations. In this contribution we will illustrate this analysis and show results based on simulations of LST-1.