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Astron. Astrophys. 363, 1115-1122 (2000)

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Absorption spectra of Mg-rich Mg-Fe and Ca pyroxenes in the mid- and far-infrared regions

C. Koike 1, A. Tsuchiyama 2, H. Shibai 3, H. Suto 4, T. Tanabé 5, H. Chihara 2, H. Sogawa 1, H. Mouri 6 and K. Okada 6

1 Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8412, Japan
2 Osaka University, Department of Earth and Space Science, Toyonaka 560-0043, Japan
3 Nagoya University, Department of Physics, Chikusa, Nagoya 464-01, Japan
4 Subaru Telescope, National Astronomical Observatory of Japan, Hilo, Hawaii, USA
5 The University of Tokyo, Institute of Astronomy, Mitaka, Tokyo 181-8588, Japan
6 Meteorological Research Institute, Nagamine, Tshukuba 305-0052, Japan

Received 8 December 1997 / Accepted 6 October 2000

Abstract

Absorption spectra of the pyroxene group have been measured in mid and far infrared wavelengths. The samples are crystalline pyroxenes (enstatite, diopside, and natural pyroxene) and amorphous pyroxenes (enstatite and diopside glass). Especially, the synthetic pyroxenes such as orthoenstatite, clinoenstatite and diopside are pure and high-quality crystalline samples. For the first time we have detected very strong and sharp peaks at about 60-70 [FORMULA] in the pyroxenes. The spectra of the pyroxenes are useful to identify the observed peaks, which have been detected by ISO on top of the broad amorphous silicates spectra of comets, circumstellar dust shells around both young stars and evolved stars. Compared to the broad features of amorphous pyroxenes, the crystalline pyroxenes show many sharp peaks in the mid and far infrared regions. Chemical composition, crystal structure, hydration, and temperature affect these spectra. The diopside may contribute to the emission feature of the planetary nebulae NGC 6302 in the far infrared region.

Key words: ISM: dust, extinction – infrared: ISM: lines and bands – stars: circumstellar matter – ISM: planetary nebulae: individual: NGC 6302

Send offprint requests to: C. Koike

Correspondence to: koike@cr.scphys.kyoto-u.ac.jp

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© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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