(Proposal ID) S12A-098

(PI) Usui, Fumihiko

(Proposal Title)
Search for Water in Outer Main Belt Based on AKARI Asteroid Catalog

(Abstract)
We propose a program to search water ice on the surface of asteroids in the 
outer main belt regions, which have high albedo measured with AKARI. The 
distribution of water in the main belt provides important information to 
understanding of the formation and evolution of the solar system, because 
water is a good indicator of temperature in the early solar nebula. The 
existence of water ice is a hot topic in the solar system studies today. 
Water ice is recently found in the outer region of the main asteroid belt 
and some of them are linked to the main belt comets. Brand-new albedo data 
brought by AKARI opens the possibility of detection of water ice on the C-type 
asteroids. Here we propose to make the spectroscopic observations with the 
Subaru telescope in the near-infrared wavelengths to detect water ice on these 
high-albedo C-type asteroids. Thanks to a large aperture of Subaru telescope 
and a high altitude of Mauna Kea, it can be only possible to observe a weak 
signal of the existence of water on the surface of asteroids with a certain 
S/N. In addition, using the imaging data taken prior to IRCS spectroscopic 
mode, we intend to seek any comet-like activities by investigating diffuseness 
of the asteroids, which can be detected by comparing the observed point-spread 
functions with those of field stars.