(Proposal ID) S16B-072

(PI) Takita, Satoshi

(Proposal Title)
Exploring the H_2O ice in WISE J180956.27-330500.2

(Abstract)
We propose to explore the H_2O ice in WISE J180956.27-330500.2 (hereafter WISE 
J1810), a star with recently-formed extremely optically thick circumstellar 
envelope. The primary goal of the proposed observation is to detect 3 mum ice 
feature. Our Subaru/COMICS observation have revealed that the object exhibits 
a silicate absorption band, indicating an oxygen-rich nature of this object. 
ALMA confirmed this conclusion by detecting SiO emission. The temperature of 
the outer boundary of the envelope estimated from SED analysis is below 200K. 
Theoretically, the H_2O ice start forming at temperatures below ~100K, and the 
crystalline / amorphous ratio depends on the surrounding environments such as 
temperature and interstellar UV. Since the formation of optically thick 
envelope around WISE J1810 took place in the past 20 years, this is possibly 
the first example of real-time observations to investigate the circumstellar 
environment.