Tests & Calibration on Ultra Violet Imaging Telescope (UVIT)

TL;DR

This paper details the tests and calibration procedures for the UVIT instrument on ASTROSAT, including optical, vibration, and thermo-vacuum tests, ensuring its readiness for multi-wavelength astronomical observations.

Contribution

It presents the comprehensive testing and calibration results of the UVIT telescopes, a first multi-wavelength mission from India, demonstrating their performance readiness.

Findings

Optical tests confirmed the targeted resolution better than 1.8 arc-second.

Vibration and thermo-vacuum tests validated the structural and thermal stability.

Calibration results ensure accurate imaging across UV and visible bands.

Abstract

Ultra Violet Imaging Telescope on ASTROSAT Satellite mission is a suite of Far Ultra Violet (FUV; 130 to 180 nm), Near Ultra Violet (NUV; 200 to 300 nm) and Visible band (VIS; 320 to 550nm) imagers. ASTROSAT is a first multi wavelength mission of INDIA. UVIT will image the selected regions of the sky simultaneously in three channels & observe young stars, galaxies, bright UV Sources. FOV in each of the 3 channels is about 28 arc-minute. Targeted angular resolution in the resulting UV images is better than 1.8 arc-second (better than 2.0 arc-second for the visible channel). Two identical co-aligned telescopes (T1, T2) of Ritchey-Chretien configuration (Primary mirror of 375 mm diameter) collect the celestial radiation and feed to the detector system via a selectable filter on a filter wheel mechanism; gratings are available in the filter wheels of FUV and NUV channels for slit-less low resolution spectroscopy. The detector system for each of the 3 channels is generically identical. One telescope images in the FUV channel, and other images in NUV and VIS channels. One time open-able mechanical cover on each telescope also works as Sun-shield after deployment.We will present the optical tests and calibrations done on the two telescopes. Results on vibrations test and thermo-vacuum tests on the engineering model will also be presented.