Normalized and Asynchronous Mirror Alignment for Cherenkov Telescopes

Abstract

Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and as they are composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment is a challenge. Here we present a computer vision based star tracking alignment method, which also works for limited or changing star light visibility. Our method normalizes the mirror facet reflection intensities to become independent of the reference star's intensity or the cloud coverage. Using two CCD cameras, our method records the mirror facet orientations asynchronously of the telescope drive system, and thus makes the method easy to integrate into existing telescopes. It can be combined with remote facet actuation, but does not require one to work. Furthermore, it can reconstruct all individual mirror facet point spread functions without moving any mirror. We present alignment results on the 4 meter First Geiger-mode Avalanche Cherenkov Telescope (FACT).

accepted for publication in Astroparticle Physics

References in corpus (6)

• The First VERITAS Telescope
• Design and Operation of FACT -- The First G-APD Cherenkov Telescope
• The optical system of the H.E.S.S. imaging atmospheric Cherenkov telescopes, Part I: layout and components of the system
• The CAT Imaging Telescope for Very-High-Energy Gamma-Ray Astronomy
• A New Mirror Alignment System for the VERITAS Telescopes
• Bokeh Mirror Alignment for Cherenkov Telescopes

Cited by in corpus (4)

• Bokeh Mirror Alignment for Cherenkov Telescopes
• The Single Mirror Small Sized Telescope For The Cherenkov Telescope Array
• Mirror Position Determination for the Alignment of Cherenkov Telescopes
• Exploring one giga electronvolt cosmic gamma rays with a Cherenkov plenoscope capable of recording atmospheric light fields, Part 1: Optics