Tomo-e Gozen logo

Tomo-e Gozen project

The scientific goal of the Tomo-e Gozen project is to develop a frontier of time-domain astronomy in hours-to-subsec time scales by wide-field and high-cadence observations with a mosaic CMOS camera on the Kiso Schmidt telescope. This project was approved as the next generation project of Kiso Observatory in 2014. A prototype model with 8 chips of CMOS image sensors was completed in 2015. Development of a final model with 84 CMOS image sensors was started in 2016 and completed in September 2019. Wide-field and high-cadence video surveys and high-speed monitoring are now ongoing.
Kiso Schmidt telescope

Kiso Schmidt telescope

Kiso Observatory with the 1.05 m Schmidt telescope was founded in 1974 in Kiso-region, Nagano, Japan. This facility is operated by Institute of Astronomy, the University of Tokyo. The Kiso Schmidt telescope has a fast optics of f/3.1 and a wide field-of-view of 9 degree diameter. A drive system of the telescope and a 16 m dome is optimized for quick wide-field surveys and quick follow-ups by Tomo-e Gozen. Automatic and remote observations are achieved by autonomous control and management software with a weather monitoring system.
Tomo-e Gozen camera

Tomo-e Gozen camera

The Tomo-e Gozen camera mounted on the prime focus of the Kiso Schmidt telescope is the world's first astronomical wide-field CMOS imager. 84 chips of CMOS image sensors enable us to obtain consecutive frames of 20 deg2 sky in 2 fps with an absolute time accuracy of 0.2 msec. Monochromatic observations are carried out to give a priority to sensitivity. The camera body consists of four quadrant units symmetrical to each other (Q1, Q2, Q3, and Q4). Video data are produced with a rate of 30 TByte/night in the 2 fps observations.
Tomo-e Gozen camera

CMOS image sensor

84 chips of 19 microns pixel 2,000 x 1,128 front-side-illuminated CMOS image sensors are set along a spherical focal plane of the Schmidt telescope with a curvature radius of 3,300 mm. The sensor chips are operated without forced cooling devices owing to a low dark current at room temperature. A low read noise of 2 e- achieves higher sensitivity than that with typical CCD sensors in short exposures.
Tomo-e Gozen server

Data processing

Server computers with 100 CPU cores and 1 PB storage are directly connected to the Tomo-e Gozen camera. The observation data are processed by advanced data science methods in real time to detect transient events and issue alerts for follow-ups. All of the raw data are deleted from the storage after five days because it is difficult to keep such a large amount of data on site for a long term. Partial data with scientifically valuable information are evacuated to long-term archive storages before the raw data are deleted.
Tomo-e Gozen Emaki

Tomo-e Gozen (巴御前)

Tomo-e Gozen (years of birth and death unknown) was a female warrior born in Kiso region, who appeared in Japanese literature the Tale of the Heike (anonymous, compiled in the 14th century). She served a military commander Minamoto no Yoshinaka (1154 - 1184) through the Genpei War (1180 – 1185). Gozen is an honorific title, usually translated to "Lady". This science project was named after Lady Tomo-e, who forcefully tore through the age of wars in Kiso region.
Tomoe Gozen (part of the image), a drawing by Shitomi Kangetsu, Tokyo National Museum
Image: TNM Image Archives