A&A 442, 507-512 (2005)
DOI: 10.1051/0004-6361:20052757
Laboratory production of magnesium sulfide grains and their characteristic infrared spectra due to shape
Y. Kimura1, M. Kurumada1, K. Tamura1, C. Koike2, H. Chihara2, 3 and C. Kaito11 Department of Physics, Ritsumeikan University, Kusatsu-shi, Shiga 525-8577, Japan
e-mail: rp092955@se.ritsumei.ac.jp
2 Laboratory of Physics, Kyoto Pharmaceutical University, Misasagi, Yamashina, Kyoto 607-8414, Japan
3 Department of Earth and Space Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka 560-0043, Japan
(Received 24 January 2005 / Accepted 13 May 2005 )
Abstract
Nanosized MgS grains, which have been considered the origin of the 30 
m emission feature of carbon-rich evolved objects, were produced
from the gas phase using an advanced gas evaporation method. The
far-infrared spectrum of cubic MgS grains showed a characteristic
absorption peak at 311 cm-1 (32.1 m) with three shoulders at
460, 400 and 262 cm-1 (21.7, 25.0 and 38.2 m). On the other
hand, when the grains were roundish or network-like, the absorption
peak at 250 cm-1 became predominant. The cubic MgS grains were
produced by direct nucleation from the gas phase. In the case of
production via a gas-solid reaction, the MgS grains were
network-like. Therefore, the formation environments of MgS grains
around carbon-rich evolved objects may be predicted from the intensity
of 310 and 250 cm-1 bands. We suggest that the origins of the
absorption band at 310 and 250 cm-1 are (100), (110) and/or
(111) surfaces of MgS grains, respectively.
Key words: methods: laboratory -- stars: AGB and post-AGB -- infrared: ISM -- infrared: stars
© ESO 2005