茅原 弘毅

The temperature dependence of diamagnetic grain orientation is reported for the first time concerning micron-sized graphite samples. An experimental method was developed for the purpose of studying the mechanism of interstellar grain alignment. The experiment was carried out in the temperature range from room temperature to 180 K, using ethanol as the suspending medium. The field of full orientation H-S decreased from 380 G to 260 G as the temperature decreased from room temperature to 180 K. The average sizes of the samples were 2.5 +/- 0.2 mu m and 3.8 +/- 0.2 mu m in diameter, and the thickness was 0.3 +/- 0.2 mu m. This temperature dependence of H-S agrees with a theoretical relation, which was derived from the theory of the Boltzmann distribution of suspended particles. A quantitative consistency in applying the conventional theory on interstellar grain alignment has not yet been achieved for the dense region, such as molecular clouds. The possibility of applying a diamagnetic-orientation experiment to the mechanism of interstellar grain alignment is discussed. The method for observing grain alignment established in the present work, can be applied for a quantitative evaluation of the star-light polarization mechanism.

The size dependence of diamagnetic orientation is reported on micron-sized graphite grains suspended in liquid ethanol at room temperature. The experiment was performed as a preliminary step to reproduce the magnetic alignment of astronomical dust particles in space. The mean grain sizes of the two samples were 2.5 and 3.8 mu m in diameter with the field of full orientation H-S being 35.9 and 29.0 mT, respectively. The present H-S obtained for graphite grains are the smallest values compared to any of the reported data on micron-sized particles. The diamagnetic orientation may be applicable to explain the grain alignment in the cosmic dense cloud of a star formation region. (C) 1998 Elsevier Science B.V. All rights reserved.

The diamagnetic anisotropy of oxide minerals are systematically studied. The field strength of diamagnetic ordering of micron-sized grains is evaluated quantitatively for various inorganic materials, for the purpose of reconsidering the possibility of diamagnetic ordering in the Universe. The possibility of a new mechanism is suggested for magnetic grain alignment on the galactic plane.