Our colleague and prominent solar physicist, Katsuo Tanaka died in Tokyo on January 2, 1990, by leukemia which he had been fighting against for many years. He was only at the age of 46.
He was born in 1943 in Tokyo. After graduating from the University of Tokyo in 1965, he proceeded to the graduate course there and obtained his Ph.D degree in 1971 for the study of the solar chromosphere based on the eclipse data.
In 1970 he moved to the Tokyo Astronomical Observatory. His interest was then shifted to the observation of solar activity, particularly solar flares, in high resolution. For two years from 1971, he stayed at Big Bear Solar Observatory and made cooperative research with H. Zirin. Their work on the large flares of August 1972 still stands as a landmark achievement in solar flare study.
After he came back to Tokyo, he worked as a key person in the Astro-A project. The Astro-A satellite, to which Tanaka gave the name "Hinotori" (meaning "Phoenix" in Japanese), observed more than 700 flares during its mission (February 1981 to October 1982). Combining the data from his X-ray spectrometer with the hard X-ray images taken by the X-ray telescope on Hinotori, he classified X-ray flares into three types: (A) hot thermal flares, (B) impulsive flares, and (C) gradual hard flares. These differences would originate, as he believed, from the environmental variety of flare sites. He summarized his view in an invited review paper in the Publications of Astronomical Society of Japan in 1987. He was awarded the Inoue Science Foundation Prize in 1985 for his achievement in flare research.
Following the success of the Hinotori project, the planning for the next mission, the Solar-A project, had started, and Tanaka was a driving force in establishing the project. In 1983, however, he started suffering from constant fever. This was an initial manifestation of leukemia which finally deprived him of his life.
Even after he knew his disease, his scientific activity never declined. In 1988 he obtained a grant and started to construct a unique telescope which observes the magnetic field, velocity field, H-alpha and white light images of solar active regions simultaneously. He believed that the energy source of flares is the emergence of magnetic flux tubes which are twisted (stressed) underneath the solar surface. His last and very elaborate piece of work in this issue of Solar Physics presents this idea.
His name Katsuo means "victory" and "quickness" in Japanese, which in retrospect might indicate his great achievements in such a short life. We deeply regret that we had lost this talented scientist.
E. Hiei and T. Sakurai