MISAO Project

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History of MISAO Project New Variable Star Discoveries

1999 Dec. 27
KenIchi Kadota, Seiichi Yoshida / MISAO Project

In 1997 April, Seiichi Yoshida, a graduate student of Waseda University, made a plan to construct a database of enormous astronomical images, set up a framework to discover new celestial objects in the database, and develop a software to discover new celestial objects as a theme of the master thesis. Because of the diffusion of cooled CCD cameras, enormous images came to be yeilded in the world, however, most of the images were not examined for new objects and only little of data in the images were utlized. In order to improve this situation, Yoshida started the MISAO (Multitudinous Image-based Sky-survey and Accumulative Observations) Project, aiming to make use of images in the world for new object discoveries and data acquisition of known objects.

In Yoshida's thoughts, image examination must be automated in the MISAO Project to deal with enormous images. So Yoshida started to develop an automated image examination system which detects stars on the images, compares them with data in CD-ROM star catalogs, measures position and magnitude of all stars and picks up candidates of new objects. This is the PIXY (PIXII: Practical Image eXamination and Inner-objects Identification) system. Yoshida spent almost all of year 1997 for development of this software. Some people offered thier images for experiments and Yoshida promoted the development with many trials and errors based on the images. In this period, Yoshida did not investigated the images for new objects because the system was still poor. However, the system came to run roughly well in early 1998.

In 1998 March, KenIchi Kadota joined to the MISAO Project and started a collaborated experimental survey and PIXY system improvement. In the early stage, Yoshida and Kadota operated the survey at the Hanadateyama Observatory (Bistar) in Miwa village, Ibaraki, using a CCD camera under Kadota's instruction. However, the survey could be run only in the weekend and the weather was not well, so the survey succeeded only 4 times during 7 months between 1998 March and 1998 September. The about 200 images helped PIXY system improvement, but no new objects were discovered.

After 1998 October, Yoshida and Kaodta purchased a CCD camera in conjunction and Kadota started survey around his home in Ageo City, Saitama, with his own instruments. Then the style is established that Kadota takes CCD images and Yoshida examines them by the PIXY system. At that time, hearing the discoveries of new variable stars by Kesao Takamizawa or the discovery of the first new variable star by Katsumi Haseda, survey for new variable stars came to be kept in mind.

In the early stage, 35-mm camera lens was used mainly for the survey. After 1999 January, 180-mm camera lens was used to detect fainter stars. But no new objects were discovered by the PIXY system comparing two images of the same area with an interval of about one month, although the ability for discovery of the system was already practical and variable stars or ghost images looking like comets were certainly detected. The framework was set up to create a database of magnitude of detected stars by the PIXY system and compare them with data in new images of the same area automatically. The check of known variable stars was also automated.

In 1999 March, Yoshida examined the image of Sakurai's object (V4334 Sgr) taken by Kadota on Mar. 22, 1999 with 18-cm f/5.5 reflector (990-mm focal length), by the PIXY system and discovered a 15-mag new object. The object was not detected on the images of Sakurai's object taken on Feb. 12, 1999 because fainter than 16.4 mag, so the system detected it as a new object. This object was confirmed on Kadota's follow up observation images taken on Mar. 31, 1999. It brightened to 14 mag and did not move. Then Yoshida announced it as the first new variable star of the MISAO Project, MisV0001, on Apr. 3, 1999.

Discovery of new variable stars are authorized in public by being published in the GCVS (General Catalog of Variable Stars) after reporting to the Sternberg Astronomical Institute, Moscow University, a consultative committee of the IAU (International Astronomical Union) and the variability was confirmed. However, this style does not function well recently because too many variable stars became to be discovered to be managed by one organization. Therefore, variable star discoverers generally named their own variable stars and publish them in papers independently, and other discoverers and researchers recognize them. In the MISAO Project, the new variable stars are named as MisV (MISAO Variables) and published.

After that, some more new variable stars were discovered from the 18-cm reflector images for follow up observation of MisV0001. At the same time, Kadota started survey with 16-cm f/3.3 reflector (530-mm focal length) in 1999 April and some new variable stars were also discovered from the survey images. Those new variable stars were around 12-15 mag. The 16-cm reflector has 1.5 x 1 deg field of view and can catch 16 mag star by 20 sec exposure. The PIXY system detects about 2000 - 7000 stars automatically from one image in the Milky Way. Considering these results, we realized that many new variable stars would be discovered by taking continuous images in the Milky Way with 16-cm or 18-cm reflector. Then the variable star survey style is established that taking images in the Milky Way with 16-cm reflector, having wider field of view.

While 8 months between 1999 April and November, Kadota ran survey 30 times and obtained about 3000 images. The surveys were operated in the open field and Kadota carried his instruments from home and assembled them every time. The instruments were not controled by computers, so all works such as taking sight, releasing a shutter, saving image files, etc., are operated by hand. All survey images were examined by Yoshida with the PIXY system. In addition, about 2000 images taken by Kadota with 18-cm reflector of comets and known variable stars were also examined in the same way. The total number of the stars detected by the PIXY system is about 15 million.

About 100 image are obtained by one survey and about 400 thousand stars are detected. But in fact, there are two images of the same area in order to reject noises, so the real number of stars is about 200 thousand. The PIXY system compares the detected stars with data obtained from the past images of the same area and select only about 200 candidates of variable stars. Then Yoshida confirms these selected candidates by eye on the images and removes uncertain or blending ones. As a result, about 50 - 100 new variable stars are discovered finally.

For perfection, Kadota also checks the images of all new variable stars discovered by Yoshida. This duplicated check style continues all through our variable star survey and suspicious stars are not announced. Because only stars with evident variability easily found by eye on the images are announced, the magnitude range of most of the new variable stars of the MISAO Project are larger than 0.7 mag. Asteroids are also checked. Taichi Kato, Kyoto University, helps us on identification with known variable stars. As a result of our continuous survey, the number of new variable stars discovered by Yoshida and Kadota in collaboration with the PIXY system reached to 739 at the end of 1999 December.

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