Earth Planets Space, Vol. 62 (No. 1), pp. 105-110, 2010
B. W. Jiang1, Ke Zhang1, and Aigen Li2
1Department of Astronomy, Beijing Normal University, Beijing 100875, China
2Department of Physics Astronomy, University of Missouri, Columbia, MO 65211, USA
(Received July 31, 2008; Revised November 28, 2008; Accepted December 9, 2008; Online published February 12, 2010)
The 21-μm and 30-μm bands are the strongest dust emission features detected in evolved low- and intermediate-mass C-rich stars (i.e. asymptotic giant branch (AGB) stars, proto-planetary nebulae (PPNe), and planetary nebulae (PNe)). While the 21-μm feature is rare and exists only in the transient PPN phase, the 30-μm feature is more common and seen in the entire late stage of stellar evolution, from AGB to PPN and PN phases, as well as in the low-metallicity galaxies: the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). The carriers of these features remain unidentified. All the 21-μm sources also emit in the 30-μm band, suggesting that their carriers may be somewhat related.
Key words: AGB stars, post-AGB stars, circumstellar dust, infrared.