The last two Spectrograph modules have come!

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We achieved a big milestone in November 2023. Finally, the four spectrograph modules have been installed at Subaru Telescope, National Astronomical Observatory of Japan, in Hawaii!!

PFS project has been developing four spectrograph modules to observe about 2400 spectra at the same time. The spectrograph modules are being developed by Laboratoire d’Astrophysique de Marseille (LAM), Johns Hopkins University (JHU), Princeton University, Brazilian consortium in collaboration with Bertin Winlight. We had preship reviews of the third and fourth modules in July and September 2023, respectively, and these modules were delivered to Subaru telescope one month later than each review.

Because a PFS engineering observation had been scheduled in December, we decided to prioritize completion of the fourth module after shipping the third, rather than integrating the third module at Subaru. We planned to integrate the two modules so that we could test the full four spectrographs in December. On the other hand, to reduce the task in the later phase, we carried out some tasks in advance for the third module after its delivery such as transporting the boxes with the optics and setting down the optical bench.

After the fourth module departed from France, we started ~25-day integration work of two modules in the end of October 2023. Three members from LAM visited Subaru telescope and worked together with Subaru staffs. In the same period, we also corrected the orientation of one of the optical components called VPHG [*], because it was revealed that VPHG had been assembled in a wrong orientation and that spectrograph throughput was therefore lower than expected.

Although the delivery of the fourth module was delayed, the great efforts of the team as well as big supports from Subaru staffs enabled us to complete integrating the two modules and correcting the VPHG orientation while LAM members were staying in Hawaii.

With the four modules, the clean room looks cramped now, but it is very impressive to see four spectrograph modules sitting together.

At this moment, all PFS instruments have been integrated at Subaru Telescope, except for the last near-infrared camera which is being developed and tested at JHU. Although our engineering observation in December was cancelled unfortunately, we are testing the cameras after integration and/or modification. We plan to validate spectrograph performance at Subaru and stabilize it for the next engineering observation.

[*] VPHG (Volume Phase Holographic Grating) is an optical component to disperse the light. It consists of glasses and gelatin in between, whose refractivity is different.