EDP Sciences
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Volume 442, Number 2, November I 2005
Page(s) 507 - 512
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20052757

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. Kaito1

1  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 )

Nanosized MgS grains, which have been considered the origin of the 30 $\mu$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 $\mu$m) with three shoulders at 460, 400 and 262 cm-1 (21.7, 25.0 and 38.2 $\mu$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

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