We are going to show the second milestone we achieved this month in this article.
At last, we succeeded in taking stars spectra during the recent Engineering observation. That is, we achieved the engineering first light!
We PFS project have carried out the on-telescope tests since Metrology Camera System was delivered to Subaru Telescope in 2018. In particular, we started engineering observations connecting Prime Focus Instrument through Spectrograph Module 1 in September 2021 (see here for details).
We have achieved various test items so far — calibrating the parameters to move the fiber positioners “Cobras” on the Subaru telescope, aligning PFI to the telescope primary mirror, testing functionalities of the guiding cameras, and taking data for the development of data processing software. Among these test items, the most important one is “to get the celestial objects on the fibers”.
Since PFI doesn’t have a camera to look at the entire field of the focal plane, PFS observes the targets whose position on the sky are catalogued from the past observations. When we observe the celestial objects, we predict the positions of the objects on the prime focus focal plane where the fibers are accommodated, and we move Cobras by measuring the fiber positions on the prime focus focal plane using Metrology Camera System (see below figure).
In this process, it is crucial to match calculation of the celestial object positions and calculation of the fiber positions. We are establishing this by observing the stars. In June 2022 we tried to put the stars on the fibers for the first time, but failed unfortunately — we found big offsets between the objects and fibers. The team discussed the reason, and tried it again in September 2022 by fixing the problem. As a result, in September 2022, we succeeded to take spectra from many stars with our Spectrograph. The images pf the Spectrograph blue and red cameras are quite impressive with hundreds of stars’ spectra!
In the coming engineering observations, we’ll improve position calculations to center the object light on the fibers, and verify the entire instrument performance.