IAU Symposium Abstract S186-006T

The Magellanic Stream and the Magellanic Cloud System
M. Fujimoto1, T. Sawa2, Y. Kumai3
1 Uedayama 4-901 Tempaku Nagoya 468, Japan: fujimoto@a.phys.nagoya-u.ac.jp
2 Department of Physics and Astronomy, Aichi University of Education, Kariya 448, Japan: sawa@auephyas.aichi-edu.ac.jp
3 Faculty of Commerce, Kumamoto Gakuen University, Kumamoto 862, Japan: kumai@kumagaku.ac.jp

Assuming a gravitaional potential of flat-rotation-curve for the Galaxy, we obtained a series of binary orbits of the LMC and SMC which endure around the Galaxy for the past 1.5 x 1010yr and reproduce both the observed geometry and dynamics of the Magellanic Stream through test-particle simulation. The orbits which satisfies the observed LMC proper motion can be uniquely determined for the near past of ~ 2 x 109 yr: An extremely-close encounter of the impact parmeter of 3-7 kpc was predicted to occur between the LMC and SMC a few 108 yr ago. Realistic binary orbits previous to ~ 2 x 109 yr ago are chosen out of our data by modeling the formation of populous star clusters in the LMC due to the close approch of the SMC.

We could not find any binary orbit whose LMC-SMC separation converges to a small but finite value as we go backward to 1.5 x 1010 yr ago. It is still difficult to conclude the common origin of the LMC and SMC as splitted from a single more massive gas cloud. We have finally applied the Galaxy-LMC-SMC system in the expanding universe where the Andromeda galaxy was close to the Galaxy about 15 Gyr ago. It is suggested that the LMC and SMC were formed simultaneously as bound to the Galaxy.