Universe of Spectroscopy

Author: Tadashi Nakajima

What would you want to introduce to readers in this series

Even though it is born like a star, it fails to become a star shining constantly the way a star does because its mass is too small. It is a brown dwarf. Theoretically, the existence of brown dwarfs was anticipated by Dr. Kumar (U.S.A.), Prof. Hayashi and Prof. Nakano (Japan) in 1963.

However, brown dwarfs are dark, and moreover it is difficult to predict the spectrum of a low temperature atmosphere. So, those searching for brown dwarfs had been groping in the dark.

For about 30 years, many candidate celestial objects were born and disappeared.

I had been a researcher at Caltech since 1992. The work was to get scientific results using Johns-Hopkins University's coronagraph mounted on the 1.5 m mirror at Mt. Palomar.

A coronagraph is an instrument that detects dark celestial objects and constructions around a bright primary star by hiding the primary star.

The science program that I chose was to explore the brown dwarf companion stars around solar neighborhood stars. According to the calculation, it was possible to detect stars with a luminosity of up to 4% of that of the darkest star. In the beginning, I had a hard time because I could not find any candidate for the companion star. But, I found a companion star that has 9% of the Sun's mass around a star called Gliese 105A in October 1994.

At the same time as the observation term, I also found a candidate companion star that was very reddish in color on 0.8 micron and 0.9 micron near Gliese 229. If the star was a real companion star, it would be main candidate for a brown dwarf.

Waiting for one year, I confirmed the same movement of the primary star and companion star candidate in the star field, and found the luminosity of the companion star was 6% of the darkest star's luminosity. Then I released the discovery of the brown dwarf.

My research field and current interests

When thinking of direct imaging of extrasolar Jovian planets, an extension of brown dwarf research, the apparent distance between the primary star and the planet and the age of the extrasolar would be problems. The extrasolar planet is easier to find when it is younger and nearer.

I figured out a way to pick out the young star from the motion of the solar neighborhood star in the galaxy; then I picked out a target star for direct imaging.

In the case of small, light M-type dwarf stars, the primary star is swung easily by a planet, and then it is easy to find the planet indirectly from changing the radial velocity of the primary star. However, we do not understand the properties of M-type dwarf stars well. So, we are trying to research the properties of M-type dwarf stars that are low temperature by spectrum in near-infrared wavelength.

Besides this, I have been writing books. I published a "Guidebook of University Students and Graduate Students Who Study Physics" (Yoshioka Shoten Publishing) and "KAKINOMOTO no Hitomaro and ONO no Komachi" (Musashinoshoin).


Tadashi Nakajima
Extrasolar Planet Detection Project Office
Job Title
Assistant Professor
Field of Expertise
Brown dwarf, Extrasolar planet