Publications of the Korean Astronomical Society pISSN 1225-1534 32: 109 ∼ 111, 2017 March eISSN 2287-6936 c 2017. The Korean Astronomical Society. All rights reserved. https://doi.org/10.5303/PKAS.2017.32.1.109 INFRARED OBSERVATIONS OF DUST AROUND HELIUM NOVA V445 PUPPIS Sayaka Shimamoto 1 , Itsuki Sakon 1 , Takashi Onaka 1 , Fumihiko Usui 1 , Takafumi Ootsubo 2 , Yasuo Doi 2 , Ryou Ohsawa 1,3 , and Daisuke Ishihara 4 1 Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 2 Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan 3 Institute of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo 181-0015, Japan 4 Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan E-mail: shimamoto@astron.s.u-tokyo.ac.jp (Received February 29, 2016; Revised October 27, 2016; Accepted October 27, 2016) ABSTRACT We detected bright mid- to far-infrared emission from the helium nova V445 Puppis in the AKARI all-sky survey data taken in 2006. Assuming an optically thin condition, we decomposed the spectral energy distribution (SED) of V445 Puppis in October 2006 by model fitting and found that the SED can be explained by a combination of cold amorphous carbon (125 K and the mass of 4.5 +6.6 −2.7 × 10 −4 M ⊙ ) and warm amorphous carbon (250 K and the mass of 1.8 +1.0 −0.5 × 10 −5 M ⊙ ). Assuming that the former is pre-existing dust formed in the past nova outbursts and the latter is newly formed dust in December 2000’s nova wind, this result suggests that the amount of dust formed around V445 Puppis in a single outburst is larger than 10 −5 M ⊙ , which is larger than those in any other classical novae ever reported. Key words: dust, extinction – infrared: ISM – novae, cataclysmic variables – stars: mass loss 1. INTRODUCTION Outburst of V445 Puppis was discovered at the end of 2000. While the distance to V445 Puppis is still unclear, 4.9 kpc (Iijima & Nakanishi, 2008; Kato et al., 2008) is adopted in this paper. Its companion is a helium star (Ashok & Banerjee, 2003). V445 Puppis is regarded as the only helium nova that has ever been observed. No hydrogen line was detected and the presence of strong C i emission was confirmed (Ashok, 2005). A signifi- cant decrease in the V-band light curve in July 2001 seems to correspond to the onset of dust formation in the nova ejecta of December 2000’s outburst (Ashok & Banerjee, 2003). Theoretical studies suggest that the white dwarf mass is very massive (M WD ≥ 1.35 M ⊙ ) and half of the accreted matter remains on the white dwarf. Consequently the white dwarf mass is expected to be increasing. Therefore, this nova is regarded as a http://pkas.kas.org candidate of Type Ia supernova progenitor (Kato et al., 2008). 2. OBSERVATIONS In this research, we analyzed observational data of the AKARI all-sky survey (Kawada et al., 2007; Ishihara et al., 2010). During the survey, V445 Puppis was observed once in October 2006, day ∼2100 from the outburst. This nova was detected in 5 bands, S9W (9.0 μm), L18W (18.0 μm), N60 (65.0 μm), WideS (90.0 μm), and WideL (140.0 μm). In order to construct the whole near- to far- infrared spectral energy distribution (SED), the near- infrared observation data collected almost at the same epoch are employed from Woudt et al. (2009). 3. RESULTS OF PHOTOMETRY The result of photometry is summarised in Table 1. The near- to far-infrared SED constructed from our observa- 109