Maunakea Telescope to Assess Planets of Nearby Stars

Figure 1: Data from CHARIS instrument during its commissioning observation run shows multiple planets around a star HR 8799. (Credit: CHARIS/Princeton Team and NAOJ)

A team of scientists and engineers recently reported successful operation of a new instrument for the Subaru Telescope that will allow astronomers to make direct observations and take spectra of planets orbiting nearby stars.

The CHARIS project is part of a long-term collaboration among Princeton University, the University of Tokyo and the National Astronomical Observatory of Japan, which operates the Subaru Telescope on Maunakea.

The instrument, dubbed CHARIS (Coronagraphic High Angular Resolution Imaging Spectrograph), was designed and built by a team led by Prof. N. Jeremy Kasdin of Princeton University.

It allows astronomers to isolate light from planets going around a star other than the sun for detailed analysis. The recent observation is known in the astronomical community as a “first light,” a first test of the instrument on the telescope to capture light from the universe that demonstrates it is operating successfully (Figure 1, above).

“We couldn’t have been more pleased by the results,” said Kasdin. “CHARIS exceeded all of our expectations. I can’t praise our joint team enough for their extremely hard work and dedication that made CHARIS a success. It is on track to be available for science observations starting in February, 2017.”

Figure 2: CHARIS (Coronagraphic High Angular Resolution Imaging Spectrograph, the red box) is attached to SCExAO (Subaru Coronagraphic Extreme Adaptive Optics, the black box) at the Nasmyth focus platform of the Subaru Telescope. (Credit: CHARIS/Princeton Team and NAOJ)

“CHARIS is a key addition to the growing exoplanet imaging and characterization capabilities at Subaru Telescope,” said Olivier Guyon, the leader of the adaptive optics program at Subaru Telescope. “With CHARIS spectra we can now do a lot more than simply detect planets: we can measure their temperatures and atmosphere compositions.”

The research team took about five years to assemble the spectrograph sealed in a 500-pound container, which operates at very cold temperature—lower than the liquid nitrogen temperature.

The spectrograph sits behind SCExAO (Subaru Coronagraphic Extreme Adaptive Optics). It channels light from the telescope and uses special patterns to separate the light from a star and the light from orbiting planets.

It is a bit like picking out a home run baseball going behind a floodlight from hundreds of miles away, said the astronomers.

Figure 3: Vapor clouds moving across a section of the planet Neptune captured in the CHARIS’s view during its commissioning observation run. (Credit: CHARIS/Princeton Team and NAOJ)

The high contrast is key, which is enabled by this SCExAO. The combination of CHARIS and SCExAO makes the overall system the most powerful tool in the world for studying other worlds.

Dr. Nemanja Jovanovic in Guyon’s team was a lead for integrating CHARIS with SCExAO (Figure 2, above).

Guyon said the integration process was very smooth “thanks to years of preparation and hard work on both the SCExAO and CHARIS side.”

The professional work of the staff in the Instrument Division at the Subaru Telescope also greatly contributed to the mounting of CHARIS, he added.