The new instrument passes a major testing milestone to capture light from multiple stars simultaneously

The international collaboration to develop the Prime Focus Spectrograph (PFS) marked a major testing milestone by successfully obtaining spectra of targeted stars.

PFS will be mounted on the 8.2-meter Subaru Telescope atop Mauna Kea, Hawaii. When complete, the instrument will use about 2,400 optical fibers to take simultaneous exposures of a large number of celestial objects in the night sky, such as stars and galaxies, and split their light into their various wavelengths. The resulting data set is called a “spectrum,” which tells researchers various details about a celestial object, including its motion, physical parameters, and age.

Using PFS, researchers will be able to uncover information that can only be seen with spectra and not visually in images. The team has been conducting tests on the telescope since 2018, but none has been more important than its latest test to capture light from celestial objects at PFS.

In late September of this year, the team conducted mechanical observations at the Subaru telescope, where they performed raster scans. These scans allow researchers to check how well their instrument is aligned with the objects they should be capturing. The fibers are placed where the researchers think the target objects should be in the focal plane of the Prime Focus Instrument (PFI), then the telescope is adjusted to a grid pattern on the sky and a spectrograph exposure is taken at each admixture location. This allows the team to measure the deviation between the actual fiber position and the actual target position.

After starting to acquire data, the team continued to take more raster scan data sets on several bright stars to correct errors and apply possible optimizations, until finally they were satisfied that the instrument was able to place the fibers very precisely on the targets of.

“The team’s efforts were again outstanding. This September run was only recently planned, but they effectively re-optimized priorities and plans and completed the required work on both hardware and software on time. And indeed the run was successful and productive .. I appreciate these and I’m really proud of the team members,” said PFS Project Director and Associate Professor Naoyuki Tamura of the Kavli Institute for the Physics and Mathematics of the Universe.

Tamura said this milestone is still a result in a single field with a specific fiber configuration. The fiber alignment with the stars has not yet reached satisfactory levels.

“But this is clearly a very encouraging achievement. Based on the fact that we were able to capture starlight from our target objects using PFS, I would say that the team has achieved Engineering First Light and entered the next instrument commissioning regime Tamura said.

“Although the PFS accommodates about 2,400 fibers, the proportion of the total area occupied by the fibers in the PFS field of view is only about 0.01% (1/10,000). In other words, even if we blindly observe the sky with PFS The fibers cannot pick up light from objects (stars and galaxies) in the sky. This is equally designed to effectively observe faint objects in the universe. The PFS team led by Naoyuki was able to accurately determine the relationship between the positions of the fibers and of the positions of the stars in the sky This success of the commissioning observation is a great first step towards the ultimate goal of revealing the nature of the dark energy occupying today’s universe from the 3D map of the universe constructed by PFS. Very exciting, “he said PFS Program Scientist and IPMU Kavli Professor Masahiro Takada;

“It is so exciting to see that we can capture starlight in our spectrograph. It opens the way to amazing science to understand how stars and galaxies formed, why the universe is aging today, what dark matter is and where the universe is headed. This milestone marks an amazing amount of work by our team. It was made possible by efforts in the fiber placement regulators developed by JPL and Caltech, the camera and spectrograph developed by John Hopkins, Princeton and LAM, optical fibers from the Brazil team and the Prime Focus Instrument from ASIAA, Taiwan. I can’t thank everyone in the team more,” said PFS Principal Investigator and Kavli IPMU Professor Hitoshi Murayama.

“It is really encouraging for those of us planning future science with PFS to actually see photons from astrophysical objects collected by the individual fibers and transmitted through the spectrographs to the detectors as a result of the integration of a remarkable instrument and a powerful telescope. We greatly appreciate the incredible effort of the instrument team,” said co-chair of the PFS Galaxy Evolution Working Group and IPMU Kavli Associate Professor John Silverman.

The data obtained by the team during this observation will continue to be carefully analyzed and discussed.

Subcomponents and subsystems of the PFS are and continue to be manufactured, assembled and tested by partner institutions in the US, France, Brazil and Taiwan before being shipped to the Subaru telescope. Operations are scheduled to begin around 2024.