WHAC Visits Subaru

Over the past few years the West Hawaii Astronomy Club has visited nearly every telescope on Mauna Kea. One glaring exception to this is Subaru, the 8.2 meter telescope belonging to NAOJ.

Subaru… Check.

Subaru is the only telescope with an active tour program. By making reservations ahead of time you can visit the interior of the facility with a guide. This made making the arrangements for a tour quite simple, even when the observatories are worried about events on the mountain. We did quite well for tour guides, Rieko Murai and Josh Walawender made the tour a bit better than the usual tour. Josh is well known to the local amateur community, bringing his own small telescopes to observe at the VIS.

The limit for any group visiting the telescope is eight due to practical considerations such as safety. Thus I had set up two tours, using both the 10:30 and 11:30 slots. This allowed most of the club an opportunity to visit the telescope. This did mean we were unable to enjoy the experience together. While we waited for our later tour I led a short walk to some interesting geologic features and one of the ancient ahu that are near the road.

Unlike the other telescope atop the mountain, Subaru uses a building the co-rotates with the telescope. This creates a very different appearance to the interior with the telescope seemingly hemmed in by the enclosure. This also offers any number of conveniences such as excellent access to parts of the telescope in way not offered by a dome. this also creates a great deal of volume for the location of instruments and workshops alongside the telescope.

Subaru is unusual for large telescopes, it was specifically designed to use prime focus instruments. By installing a specially designed instrument in the position normally occupied by the secondary mirror, the telescope takes advantage of the full eight meter aperture while still allowing for a wide field of view. Here is where spectacular cameras like Hyper Suprime-Cam are positioned.

A large bay near the top of the building provides storage and work space to support the secondary mirrors and prime focus instruments. Each instrument sits in a large rotary carriage for stowage. A robotic arm assembly allows the instrument to be removed from the carriage and moved into the telescope enclosure. From there a special attachment to an overhead crane takes the instrument and lifts it into the telescope.

During the tour we visited the prime focus bay where we saw Suprime Cam and Hyper Suprime Cam. We took a close look at the interesting FMOS fiber-fed multi-object spectrograph and viewed the telescope from a catwalk high above the observing floor.

A visit to the main floor at the base of the telescope allowed a close look at the cassegrain focus and the instruments located there. Here there is a special cart used for exchanging the cassegrain instruments that mirrors the robot in the prime focus bay. The main floor also provided an opportunity for a group photo in front of the telescope.

Despite a generous amount of time and so many answered questions we were ready for more, the tour all too short. It was a great day and another wonderful experience atop the mountain.