Home Page       Tue Aug 19 18:00:36 JST 1997

Examples of new objects discovery from images

Now many teams at large observatories or some people are already working on discovery of new objects and obtaining good results. Here I show you two cases of them, the Solar and Heliospheric Observatory (SOHO) team and a Japanese amateur Takao Kobayashi, then grasp of the current situation of discovering projects and think of problems to be solved.

The SOHO team is monitoring the sun since 1995 December with a coronagraph loaded on a satellite in a Lagrangean point between the earth and the sun. Though their main purpose is not a new objects discovery, the SOHO team started new comets search near the sun in earnest in 1997, because many Kreutz comets, famous for their grazing to the sun's surface, has been caught accidentally. At first they found out the objects visually but they completed an automated detecting software. As you know they are now examining old images with the software, and discovering many comets in succession.

The way of the SOHO team is to detect moving objects making difference of successive images. At first, they gain a standard deviation of all pixels and adopt twice or three times of as a threshold. If the difference is more than the threshold, it is regarded as a real object. If less than the threshold, it is regarded as a noise.

The SOHO team's result of the old comets discovery by a retrospective check with an automated software shows the truth that it is so hard to discover new objects from images taken for another purpose and strongly implies that unknown objects are buried in unchecked images. Let me consider of a comet C/1996 J1 ( Evans-Drinkwater ), though it is not a new object. It has been too near to the sun in order to observe on the ground for a long time, and in 1997 May, it was cleared that the comet had bursted out during the blank period. This comet was near by the sun in 1996 December and 1997 January, so it might be in the SOHO's image. Let me also consider of a periodic comet 85P/Boethin, which has not yet observed until 1997 August, because it has been too near to the sun. This comet might be in the SOHO's image, too. Though the SOHO's main purpose is to observe the sun, the images also contain important information on other targets, like on these comets. Actually an image for one purpose often contains very significant information for other purposes. However, it is rare that the images come to be researched for other purposes as in the case of the SOHO team. In many cases the images are examined only for the main purpose and other significant information are never in the public.

As the second case, a typical amateur in Japan, Takao Kobayashi, are detecting new objects from images with his own system. The results are the enormous new asteroids discovered from 1996 to 1997 and the discovery of a comet P/1997 B1 ( Kobayashi ).

Kobayashi's way is finally to detect new objects visually with eyes on a computer display. Therefore I guess it takes some time and there are some possibility to miss objects at the detection. In addition, his system is not a public software, and is used only for his check of his own images. Because his observation are only during winter, the system is dead for summer.