the Tomo-e Gozen project

The Institute of Astronomy, the University of Tokyo Kiso Observatory

UTokyo starts a full operation of Tomo-e Gozen.

The Tomo-e Gozen system has been being developed for the 105-cm Kiso Schmidt telescope by mainly Kiso Observatory, Institute of Astronomy, School of Science, the University of Tokyo since 2014, and finally completed. The University of Tokyo starts a full operation of Tomo-e Gozen in October 2019.

Japanese

Overview of the Tomo-e Gozen project

Tomo-e Gozen is an observation system including the world’s first astronomical wide-field movie camera and artificial intelligence software, which is developed to explore the universe changing with short timescales (Fig. 1-3). The Tomo-e Gozen camera covers a field-of-view of 20 square degrees on the sky at once, corresponding to a total area of 84 full-moons, by 84 chips of high-sensitivity CMOS image sensors with a total 190 million pixels. This camera produces movie bigdata of the sky of 30 TBytes, corresponding to about 10 thousand cinemas, in a night. The software of Tomo-e Gozen can detect variations of brightness and positions of stellar objects precisely by comparing with data sets taken in past observations in real-time (Fig. 4-10).

   
(left: Fig. 1) Scientific meaning for studying the changing universe. (right: Fig. 2) Phenomena with timescales shorter than 1 day have not been sufficiently explored. A main purpose of Tomo-e Gozen is to reveal the unexplored universe.

   
(left: Fig. 3) Tomo-e Gozen in cyber space. (right: Fig. 4) Overview of the Tomo-e Gozen camera.

   
(left: Fig. 5) Pictures of development works. (right: Fig. 6) Picture of the Tomo-e Gozen camera mounted on the focal plane of the Kiso Schmidt telescope.

   
(left: Fig. 7) Comparison of field-of-views of representative wide-field cameras. (right: Fig. 8) Field-of-view of a single sensor on the Tomo-e Gozen camera corresponds to an area of a full moon.

   
(left: Fig. 9) Example of detected trails of fast-moving objects. (eight: Fig. 10) Movie files of the Milky Way taken by the Tomo-e Gozen camera.

1. Movie 1(mp4): M27(planetary nebula) -> Altair (first-magnitude star） -> M11（open star cluster）
2. Movie 2(mp4): Sky areas 53-arcmin apart from (1) in the south direction
3. Movie 3(mp4): Meteor and its trail crossing behind thin clouds

These movies are played at five times the real speed. Each movie is taken by a single sensor. Each exposure time of consecutive frames is 0.5 seconds.

Observation system

The large-format high-sensitivity CMOS image sensors on the Tomo-e Gozen camera are not required to be cooled down like image sensors on other astronomical instruments because low dark current and low readout noise are achieved even at room temperature. This allows us to make a large size camera system (Fig. 11). The 84 chips of CMOS sensors are placed precisely along a spherical focal plane of the Schmidt telescope (Fig. 12). The Tomo-e Gozen camera and the telescope are automatically controlled by software with optimization algorisms on a computing system directly connected to the camera. Observation data is also automatically processed by software with machine learning models (Fig. 13). Since the observation data taken by the Tomo-e Gozen camera is too large, 30 TBytes/night, to keep it for a long time, it is deleted from a data storage in 7 days after the observations. The analysis software of Tomo-e Gozen saves only “attractive information” to a long-term storage before it is deleted. Astronomers mine information interesting for themselves from the long-term storage by onsite computers. When interesting stellar objects and events are found, alerts for follow-up observations are sent to other observatories in the world quickly. In order to build a quick and smooth alert system, we will connect between an information center at Kiso and a data center at the Kashiwa campus of the University of Tokyo via a high-speed network (Fig. 14). Tomo-e Gozen automatically creates observation plans and executes them based on demands of astronomers, and reoptimizes the running plans according to changing weather conditions and additional astronomical information such as detections of transient events by other telescopes (Fig. 15).

   
(left: Fig. 11) Overview of CMOS image sensor. (right: Fig. 12) Overview of camera unit.

   
(left: Fig. 13) Overview of onsite computing system. (right: Fig. 14) Flow of data obtained by Tomo-e Gozen.

(Fig. 15) Intelligent automatic observation system of Tomo-e Gozen.

Wide-field movie survey of the sky

Over 100 nights every year, Tomo-e Gozen carries out movie surveys of the sky repeatedly in a night (Fig. 16-18). These survey observations enable us to detect more than 130 thousand events of transient phenomena with short timescales of 1 second to 1 hour by monitoring brightness and positions of about 100 million sources on the observation images (Fig. 19-22). There is no precedent for such wide-field movie survey of the sky.

   
(left: Fig. 16) Overview of wide-field movie observations of the sky by Tomo-e Gozen. (right: Fig. 17) Scanning pattern. It fills gaps between sensors by moving the telescope slightly in 2x2 or 2x3 patterns.

   
(left: Fig. 18) Example of the wide-field movie survey. (right: Fig. 19) Wide-field image produced by stacking the survey data taken in a night.

Movie (mp4): Foot prints of Tomo-e Gozen in a wide-field movie survey.

   
(left: Fig. 20) Candidates of brightness variables detected in the wide-field movie survey. (right: Fig. 21) Candidates of fast-moving objects detected in the wide-field movie survey.

(Fig. 22) Strong points of the Tomo-e Gozen data.

Expected results

It is expected that transient events found by Tomo-e Gozen include many scientifically important phenomena such as supernovae just after explosions and asteroids with possibility of collision to the Earth (Fig. 23-24). We have a collaboration plan between Tomo-e Gozen, the gravitational wave observatory KAGRA, and the 3.8-m SEIMEI telescope, which is operated by Kyoto university and NAOJ at Okayama, to reveal origins of gravitational waves (Fig.25). Since bigdata obtained by Tomo-e Gozen every night contains many events appearing on the sky comprehensively, data driven astronomy based on cooperation among multiple fields such as studies on Earth’s upper atmosphere, monitoring of satellites and space debris, and social outreaches with real science data is expected (Fig. 26).

   
(left: Fig. 23) Expected science results. (right: Fig. 24) Continued.

   
(left: Fig. 25) Multi messenger astronomy by the gravitational wave observatory KAGRA, Tomoe- Gozen, and the 3.8-m SEIMEI telescope. (right: Fig. 26) Utilization of sky bigdata via high-speed networks.

(Fig. 27) Summary of the Tomo-e Gozen project.

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Reference

News release of Canon Inc.
"Kiso Observatory, University of Tokyo, commences full operation of 'Tomo-e Gozen,' a new observation system equipped with 84 Canon ultra-high-sensitivity CMOS sensors”

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Credit

Please credit images and movies on this site to Kiso Observatory, the University of Tokyo.
ex) Image credit: Kiso Observatory, the University of Tokyo