To improve the instrument performance 2

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Before the engineering observation in March 2024, we PFS project carried out two major modification works at Subaru telescope.

One of them is realignment of Metrology Camera System. “Metrology Camera System (MCS)” is the instrument installed on Cassegrain focus of Subaru telescope, and namely measures the fibers position on the prime focus plane. In fact, there was an accident during the instrument exchange in December 2023, which resulted in significant change of the image quality. Fortunately, the impact of image degradation didn’t affect on-telescope test in December 2023. However, we decided to align camera module of MCS again for further observations and long-term operation. In January 2024, the team at Academia Sinica, Institute of Astronomy and Astrophysics (ASIAA) in Taiwan visited Subaru and carried out realignment work. At the time, we adjusted the tilt of the camera module so that the sport size gets more uniform across the camera image.

The other work is modification of Spectrograph to recover its throughput. As reported in the previous article, we modified orientation of the optics called VPHG when we integrated the last two Spectrograph modules at Subaru Telescope. At that time, we modified three out of four kinds of VPHG, because VPHG for medium resolution has two big glasses on its sides, which requires more discussion to develop different strategy and method. Modification jigs (see photos in below, left side) were designed and produced by Princeton University and Johns Hopkins University discussing with Laboratoire d’Astrophysique de Marseille (LAM). In February 2024, team from LAM visited to Subaru and modified VPHG orientation to complete throughput recovery in all wavebands and resolution modes.

In the engineering run in March, we tested instrument performance and optimized software after these modifications.