Enhanced Vision for the Subaru Telescope

The Subaru telescope has been equipped with a new adaptive optics system that has enhanced its already impressive vision by a factor of 10. The new system uses a laser beam to project an artificial guide star into the sky at an altitude of 90 km. Computers can then calculate the distortions from the Earth’s atmosphere and adjust the shape of a special mirror to remove those distortions.

On October 9, 2006 the Subaru telescope researchers used a new adaptive optics system to obtain an image of the Trapezium region of the Orion Nebula. A comparison of this new image with a first light image taken when the Subaru telescope first began observing in 1999 (Figure 1), shows a dramatic increase in contrast and detail in the higher-resolution image. With the new system in place, including a newly installed laser guide star system, to measure and correct for the effect of turbulence in real-time, Subaru’s eyesight has been improved by a factor of ten, giving astronomers a clearer view of the universe.

Adaptive optics and laser guide star technology are important to astronomers because a ground-based telescope’s ability to resolve spatial detail is limited by turbulence in Earth’s atmosphere. If the Subaru telescope were in space (without atmospheric interference) it could achieve an angular resolution of 0.06 arcseconds for light with a wavelength of 2 microns.

In practice, even with the excellent observing conditions on Mauna Kea, the typical resolution Subaru can obtain is 0.6 arcseconds because of the atmospheric turbulence that causes light traveling from stars and other objects to twinkle and blur. Fortunately, adaptive optics technology removes the twinkle and eliminates the blur. This allows astronomers to see greater detail in the objects they observe.

Subaru’s adaptive optics development team has been working on replacing its older 36-element adaptive optics system with an improved 188-element system for the past five years. At the same time, the team also developed and installed a new laser guide star system that allows astronomers to create an artificial star anywhere in the sky. They use light from the artificial star to measure the twinkle brought on by the atmosphere. That information is then used by the adaptive optics system to deform a special mirror that removes the twinkle and clarifies the view.

On October 12, 2006, researchers projected a laser beam into the sky to produce an artificial star in the sodium layer of Earth’s atmosphere, at an altitude of about 90 kilometers. (Figure 2 and 3) Subaru’s laser guide star system is the 4th system to be completed in the world for 8-10m telescopes, and its use of unique solid-state laser and optical fiber technology, both developed in Japan, represents a new and original contribution to the field.

Together, both systems open up a larger portion of the sky to observations with adaptive optics and allow Subaru to reach its theoretical performance limit (Figure 4).With the addition of these new systems, the Subaru telescope will enable astronomers to study objects that were previously unobservable, such as the detailed structure of faint distant galaxies and stellar populations of nearby galaxies. They will also be able to do more detailed imaging and spectroscopy of quasars and gamma-ray bursters.

The research and development of the new systems was supported by a grant from MEXT, the Japanese Ministry of Education, Culture, Sports, Science and Technology.

The following people at Subaru Telescope and the National Astronomical Observatory of Japan contributed to this research: Masanori Iye (Principal Investigator), Hideki Takami (Head of the Adaptive Optics Project), Yutaka Hayano (Leader of laser guide star system development), Makoto Watanabe, Masayuki Hattori, Yoshihiko Saito, Shin Oya, Michihiro Takami, Olivier Guyon, Yosuke Minowa, Stephen Colley, Michael Eldred, Mathew Dinkins, Taras Golota.

Original Source: Subaru News Release