Subaru Telescope 2.0

Four Key Instruments

The Subaru Telescope has a tremendous advantage in observing a wide field of view with high spatial resolution in visible light. Hyper Suprime-Cam (HSC), mounted on the prime focus at the top of the telescope, offers an ultra-wide field. In the mid-2020s, Subaru will add Prime Focus Spectrograph (PFS) on the prime focus. Moreover, ULTIMATE-Subaru, a wide-field, high-resolution infrared instrument, is scheduled to start observation in the latter half of the decade. With these new instruments, Subaru will realize unprecedented large-scale survey observations in visible and infrared light.
Identifying exoplanets (extrasolar planets) requires a specialized instrument. InfraRed Doppler (IRD) is being used in this search for Earth-like planets.

The key instruments for Subaru Telescope 2.0 have the following three features.

1. Imaging and spectroscopic instruments at the primary focus (primarily visible light)

Instruments: HSC, PFS

Since 1999, the Subaru Telescope has been exploring the Universe by taking advantage of its wide field of view capabilities. In general, the larger the aperture of the telescope, the smaller the area of the sky it can observe at once. The Subaru Telescope, however, realizes a wide field of view by mounting a camera on the prime focus. In 2013, Hyper Suprime-Cam (HSC), whose sky coverage is as large as nine full Moons, started operation. The Subaru Telescope’s most extensive observing program, the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), began in 2014 and lasted approximately 330 nights. The program surveyed an unprecedented area of the sky using HSC.
In the mid-2020s, Prime Focus Spectrograph (PFS), an ultra-wide field multi-object spectrograph, will begin observation, taking advantage of its prime focus to the spectrograph, to obtain spectra of 2,400 objects at one time. With PFS, the Subaru Telescope will have 50 times the field of view and 20 times the number of simultaneous spectroscopic objects compared to other conventional instruments.


2. Infrared instrument with a wide field of view, high sensitivity, and high spatial resolution

Instrument: ULTIMATE-Subaru


The revolution in the wide field observation capability of the Subaru Telescope is not limited to the visible light wavelength range. The technique called "Adaptive Optics (AO)" has been applied to correct the atmospheric turbulence in real-time. A Laser Guide Star (LSG) system generates an artificial guide star, enabling us to measure and minimize the effects of the turbulence. Adaptive optics is a powerful technique that allows us to obtain sharp astronomical images as if we were observing from outside the atmosphere. However, with conventional technology, there is a problem obtaining sharp images with only a narrow field of view. "High spatial resolution" and "wide field of view" are competing elements. To overcome this obstacle, "ULTIMATE-Subaru," a wide-field high-resolution infrared instrument is under development, expected to be completed in the latter half of this decade. The system launches multiple laser beams into the sky, concentrating on correcting the effect of atmospheric turbulence near the ground's surface. Such systems are called Ground Layer Adaptive Optics (GLAO). The instrument is designed to realize an adaptive optics system with a field 200 times wider than that of the conventional adaptive optics of the Subaru Telescope, creating the largest field of view among the biggest telescopes in the world.

3. Specialized instrument used in the search for exoplanets

Instrument: IRD

The study of exoplanets (extrasolar planets) is one of the main themes of modern astronomy. InfraRed Doppler (IRD) is a specialized instrument that aims to detect earth-size planets orbiting stars that are fainter and cooler than the Sun and to search for habitable worlds in which liquid water may exist. The operation of IRD started in 2018. Among various approaches for exoplanets, the Doppler method for detecting wobbles of a host star has been most frequently applied to visible-light observations. IRD enables infrared observations that can detect wobbles of a star with an accuracy of about the speed of a human walk, approximately 2 meters per second. As of 2022, IRD has the highest accuracy for velocity determination among working infrared instruments for 8-10 meter telescopes. IRD is essential not only in the search for exoplanets but also for investigating the properties of low-temperature stars, which have yet to be well-studied. In addition, SCExAO and CHARIS / VAMPIRES — adaptive optics instruments that enable direct imaging, spectroscopy, and polarization observation of exoplanets —are also important instruments in this field.


The History of Instruments leading up to Subaru Telescope 2.0


The four key instruments for Subaru Telescope 2.0 follow the mainstream of instrument development for the Subaru Telescope so far. The history of the instruments is summarized in this chronological table according to their features. For instruments not listed here that are in-service or already decommissioned, see the web page “About Subaru Telescope” > “Observational Instruments.”

Wavelength Regime


The Subaru Telescope has an imaging camera and a spectrograph covering visible light to infrared. HSC is a camera for imaging in visible light, and PFS is a spectrograph primarily in visible light. ULTIMATE-Subaru has both spectroscopic and imaging capability in infrared. IRD is an instrument focusing on ultra-high precision velocity measurements with high spectral resolution in the infrared range. In this figure, wavelengths shorter than 1 micrometer are displayed as visible light, whereas those longer than 1 micrometer are displayed as infrared.