Dust formation by massive stars studied by infrared observations with AKARI/IRC and Subaru/COMICS

Itsuki Sakon1*, Takashi Onaka1, Kentaro Asano2, Ryou Ohsawa1, Hidehiro Kaneda3, Takao Nakagawa4, Takaya Nozawa5, Yoshiko Okamoto6, Takuya Fujiyoshi7, Fumihiko Usui4, Hirokazu Kataza4, Hideo Matsuhara4, and Hiroshi Murakami4
1Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2Institute of Astronomy, University of Tokyo, 2-21-1 Ohsawa, Mitaka, Tokyo 181-0015, Japan
3Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
4Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara 229-8510, Japan
5IPMU, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8568, Japan
6Institute of Astrophys. and Planetary Sciences, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan
7Subaru Telescope, NAOJ, 650 North A'ohoku Place, Hilo, HI 96720, USA

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Recent AKARI/IRC observations of SN2008ax in NGC4490 on the day 98 has revealed the presence of near-infrared excess emission. This emission can be interpreted as the re-radiation from the pre-existing circumstellar amorphous carbon dust of a color temperature of 767±45 K and the mass of 1.2+0.4-0.3 X 10-5 M or silicate dust of 885±60 K and 6.8+2:5-1.7 X 10-5 M, which may have been formed in the mass loss wind from the OB/WR progenitor in an interacting binary system. In order to investigate the on-going dust formation by WR binary systems, the mid-infrared observations of the Galactic WR binary WR140 were carried out with Subaru/COMICS on 1st August 2009. 11.7μ image of WR140 has shown that the dust cloud formed during the previous periastron passage in 2001 has expanded up to 2.6” away from the stellar core with an expansion velocity of 2.7±0.3 X 103 km s-1. The high-spatial resolution N-band spectrum of dust structures around WR140 was obtained for the first time and broad band features at ~8.3 μm and ~12.2 μm were detected. The possible carriers of these emission bands are discussed.

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Keywords : stars: formation: star clusters - stars: initial mass function.