Teriaca, L. ; Schühle, U. ; Aznar Cuadrado, R. ; Heerlein, K. ; Berghmans, D. ; Auchère, F. ; Gissot, G. ; Kraaikamp, E. ; Harra, L. ; Long, D. ; Stegen, K. ; Verbeeck, C.

Poster presented at Solar Orbiter 8, Belfast on 2022-09-12

Abstract: HRILYA is the intensified high-resolution telescope of the EUI instrument operating at the Lyman alpha line of Hydrogen. The telescope obtained the first light images on April 12th 2020 and, since then, has acquired images of the solar surface on about 80 different days until June 2022 (last analysed data). Some of these observations were obtained specifically to calibrate the instrument response to different settings of the high voltages and of the CMOS/APS sensor of the camera and integrate the available measurements taken on the ground. This pre-calibration step is essential in comparing data taken with different setups. By considering only data taken near disk centre, using the full available field of view, binning not greater than 2⨉2 and exposure times and high voltage settings suitable for scientific observation, we built a dataset of more than 15000 images. These images were carefully analysed to retrieve information on the average signal and contrast as a function of time and distance between the spacecraft and the Sun. These results show the evolution of the instrument throughput and (part of) performance through the first two years of life. Throughput and contrast appear to reduce over the considered period, with the situation worsening significantly during March 2022 apparently in correspondence with the first perihelion (below 0.35 AU). Besides solar images, UV LED that illuminate it directly (without making use of the optical elements) can also stimulate the camera. We also analyse LED images taken at the beginning of the mission and compare them to a set acquired recently (June 12th 2022) to try to understand whether the problem concerns the camera or the optical elements. This latter analysis is subject to the availability of the recent data and whose downlink time is expected to be of several weeks.

Keyword(s): Solar Orbiter ; EUI
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