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Paper: Far-IR Imaging Survey of the Extended Dust Shells of Evolved Stars with AKARI
Volume: 418, AKARI, a Light to Illuminate the Misty Universe
Page: 127
Authors: Izumiura, H.; Ueta, T.; Yamamura, I.; Nakada, Y.; Matsunaga, N.; Ita, Y.; Matsuura, M.; Fukushi, H.; Mito, H.; Tanabe, T.
Abstract: A Far-IR imaging survey of the circumstellar dust shells of 144 evolved stars has been performed as a mission program with the Far-Infrared Surveyor (FIS) on the infrared astronomical satellite AKARI. The survey has produced simultaneous maps of 10′×40′ areas in the four FIS bands at 65, 90, 140, and 160 μm for most of the objects. Maps of 10′×20′ area have been taken for the remaining 17 fainter objects. Extended dust shells, most of which show departure from circular symmetry or offset with respect to the star, have been found in both dozen oxygen-rich and dozen carbon-rich evolved objects. In the carbon star U Hya, however, a circular dust shell centered at the star of ∼130′′ (3.2×1017 cm, ∼0.1pc) in radius is revealed in the four FIS bands, for the first time by direct imaging in the far-infrared. The FIS images of U Hya are analysed by a simple detached dust shell model. The best fit model gives the inner radius of 2.4×1017 cm, thickness of 2.2×1017 cm, indices of power-law dust opacity and dust density distribution of 1.1 and 2.5, respectively. Dust mass of 3×10−4 Msun is obtained for the case of a dust opacity of 25 cm2 g−1 at 100 μm. A thinner shell with a smaller index of the density distribution could also be viable. Possible origin of the dust shell of U Hya is discussed.
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