Mauna Kea telescopes step up collaborations

If the Gemini and Subaru observatories pull off a proposed joint Wide-Field Multi-Object Spectrograph (WFMOS), the collaboration would epitomize nascent trends in astronomy toward both time-swapping and large “campaign” projects.

The observatories on Mauna Kea have dabbled in time-swapping for a couple of years. Since the beginning of last year, for example, Gemini and Keck have traded five nights a semester. The arrangement gives Keck users access to Gemini’s mid-infrared imager and spectrometer, and the Gemini community uses Keck’s high-resolution optical spectrograph. On a smaller scale, Keck and Subaru have swapped nights here and there, and, starting later this year, Gemini and Subaru plan to exchange five nights a semester.

But the WFMOS collaboration would be much more ambitious, says Gemini acting director Jean-René Roy. “Japan effectively becomes a new partner in Gemini, and Gemini becomes a new partner in Subaru. This is really a new paradigm.” The twin 8.1-meter Gemini telescopes, one on Mauna Kea and the other in Chile, have seven member countries, with the US holding a 50% share. Subaru is Japan’s only 8-meter-class telescope; the country’s next-largest telescope is 1.88 meters in diameter.

“Joined at the hip”

The idea for WFMOS came from the Gemini community. A key motivation for the instrument is to probe dark energy in a new way, by measuring the distribution of galaxies (see the story on page 32). “We would measure what amounts to a fundamental scale in the universe at different epochs—before and after the switch 5 billion years ago from a matter-dominated to an energy-dominated universe,” says Doug Simons, Gemini’s associate director for instrumentation. “The point is not just to conclude we are in an accelerating universe, but to figure out the rate at which the universe is accelerating.”

WFMOS would also be used for a second science campaign, on galactic archaeology. From the abundance of elements and stellar velocities revealed in star spectra, stars would be traced back to the specific molecular clouds where they were born, says Simons. “The idea is to DNA-type one or two million stars, and thus decompose the family history of our galaxy, and for the first time make an assessment of how the galaxy was put together. We’ve never seen a galaxy forming.”

But WFMOS, which would have around 10 spectrographs to record 20 000 spectra per night, is too bulky for Gemini. “Gemini is light, fragile, dynamic. It could not accommodate such an instrument without a major transformation,” says Roy. “The cost would have been outrageous.”

It turns out that Subaru’s rigid, sturdy structure is a good fit. Moreover, the Subaru community was already planning to enlarge its telescope’s wide-field corrector for a new imager, HyperSuprime-Cam, which would give the widest field of view on any 8-meter or larger telescope. Now Gemini and Subaru are looking into designing the corrector to be compatible with WFMOS too. A weak-field gravitational-lensing survey planned for HyperSuprime-Cam, says Satoshi Miyazaki, the lead designer for the imager, “directly probes dark matter, and the distribution of dark matter depends on dark energy.” The two instruments, adds Simons, “are joined at the hip politically, scientifically, and technically.”

In exchange for hosting WFMOS, the Japanese astronomy community would get access to both Gemini telescopes for perhaps a total of half the number of nights that Subaru devotes to the joint projects; over five years or so, a couple hundred nights each would go to the dark-energy survey and the galactic archaeology project. The partners would split the cost of WFMOS—estimated by Gemini at $65 million—and would build it jointly.

Campaigns and collaboration

With instruments growing in complexity and price, it’s no longer affordable for each telescope to be outfitted with every type of instrument. “The trend is to concentrate on a few instruments where we think [a particular] telescope is best designed to produce the highest performance,” says Roy. Campaign science with large telescopes, he adds, “is a shift. We are moving in the direction of particle physics, the way it happened in the 1960s and 1970s. The questions are bigger, and you need bigger tools.”

One downside of campaign science, the squeezing out of principal investigators, is diluted by collaborating; with WFMOS, that burden would be spread across three telescopes—Subaru and the Gemini twins. “I feel we have to keep at least 50% of the time on all our telescopes for PI science,” says Roy.

Competition with Europe’s Very Large Telescope in Chile adds fuel to the move toward sharing telescopes in the North, Roy says. “[The Europeans] have basically decided that they will cream the US. They want more papers, more citations. They have a huge machine. We cannot be balkanized anymore.” In the future era of 30-meter-class and larger telescopes, adds Subaru director Hiroshi Karoji, “we will all be partners. So it’s natural to start sharing the coverage of wavelengths and resolving power among several telescopes.”

But for the WFMOS collaboration to go forward, scientific, technical, financial, political, and logistical details need to be worked out. In the WFMOS design, a balance needs to be struck between the technical demands of the campaigns and the broader needs of PI science. And the two observatories will have to coordinate development of future instruments so that they are attractive for both user communities, says Karoji. In the swaps undertaken so far, observatories select proposals from their own community to use the other facility, and time is allocated and data are archived according to the host observatory’s rules.

Other logistical challenges include designing, building, and managing the instrument and agreeing on how to share credit for any major discoveries. Those issues are not showstoppers, says Doug Welch, an astronomer at McMaster University in Hamilton, Ontario, and the incoming chair of the Gemini board. “The challenge right now for Gemini and the Japanese community is to figure out a timely process for getting WFMOS under way.”

Sanity checks

Gemini has put the science case for WFMOS “through numerous reality checks and sanity checks,” Welch says. In Japan, the debate over WFMOS is just heating up. While there are theoretical physicists in Japan who focus on dark energy, among traditional users of Subaru the field is “almost nonexistent,” says Karoji. “So it’s a hard task for me to convince the community to do this.” Swapping time “drastically changes the mode of life” for Japanese astronomers, he adds. “To have limited access to Subaru, and have to go to Gemini for observing, is a huge change. It’s normal that there is a debate.”

Subaru is about five times over-subscribed, and Japanese astronomers worry that by devoting time to the WFMOS campaigns, other instruments on their telescope will be shut out. Some say they simply aren’t interested in the instruments available on Gemini. They worry, too, that grant money for fields outside of dark energy and cosmology will dry up. “By far the most important factor to achieve consensus of the Subaru user’s community,” says University of Tokyo cosmologist Yasushi Suto, a supporter of the project, “is the visibility of Japanese participants in planning and running WFMOS science.”

Despite the challenges, says Karoji, “I think a compromise, mutual understanding, is possible, because [WFMOS] could be used in many ways and in many fields of science. Dark energy is one of them, but large-scale structure development, the evolution of galaxy morphology, these basic questions are favorite themes in the Japanese astronomy community.” Through Gemini, Japanese astronomers would gain access to the southern sky. And the WFMOS project would announce Japan as a major player in astronomy. “It is a good opportunity for Subaru to have a big international collaboration,” says Naoshi Sugiyama, an astronomer at Subaru’s parent body, the National Astronomical Observatory of Japan.

At this point, says Karoji, “I have not one yen [to pay for WFMOS]. We need two things, approval in the community and approval from the NAOJ headquarters for funding.” Gemini and Subaru are moving forward with design plans and seeking money. The plan is to have a conceptual design by spring 2007 and a decision on going ahead later that year.

Another project in the making for a bit further in the future would use optical fibers to link a half dozen Mauna Kea telescopes into an optical interferometer. “The classic way to have done that with multiple telescopes would be to build great big tunnels between them and have optical rays in vacuum pipes,” says Keck director Fred Chaffee. With fibers, he adds, “The technical challenge is inversely proportional to the wavelength, so with optical wavelengths a million times shorter than radio, everything becomes literally a million times more difficult. It’s a completely different ball game.” The two Keck telescopes were linked last year, demonstrating the proof of principle. The project is called OHANA (Optical Hawaii Array for Nanoradian Astronomy), the Hawaiian word for “family.”