2026AJ....171..184D

The Ultra-Violet Imaging Telescope (UVIT) is one of the five payloads on board the first Indian multiwavelength astronomical observatory, AstroSat, launched by the Indian Space Research Organisation on 2015 September 28. UVIT, designed for simultaneous imaging in the far-ultraviolet (FUV; 1300-1800 Å) and near-ultraviolet (NUV; 2000-3000 Å) channels, has completed 9 yr in orbit in 2024 despite the failure of the NUV channel in 2018. As the FUV optics is subject to possible reduction in sensitivity due to microscopic amounts of contaminants, we used the FUV data acquired by UVIT over the past 9 yr on the open cluster NGC 188 and the white dwarf HZ 4 to study sensitivity variations in the UVIT FUV channel. Our findings indicate no significant reduction in the sensitivity of the FUV channel over the last 9 yr, with no significant episodic variations due to unknown causes.