(Proposal ID) S13B-128

(PI) Ootsubo, Takafumi

(Proposal Title)
Properties of cometary crystalline silicate before and after perihelion passage

(Abstract)
Crystalline silicate is sometimes observed in comets as an 11.3-micron resonant
 emission feature, and may be used for probing the early solar nebula. Because 
the formation of the crystalline silicate requires high temperature, they are 
thought to be born from amorphous silicate at the inner region, and then 
transported toward the outer regions where comets were born. This 
transportation can produce the difference in the crystalline fraction in the 
cometary silicate dust between two dynamical types of comets, Oort-cloud 
comets (OCs) and Ecliptic comets (ECs), due to the different heliocentric 
distances of their birth places. The study of peak wavelengths in crystalline 
features is important to investigate the conditions of the crystalline 
silicate formation as well. Thus far, we don't have enough OC samples, while 
we have observed several ECs. Fortunately, we can observe three comets in this 
semester. In particular, C/2012 S1 (ISON) is a bright sungrazing comet, and we 
might expect possible splitting and exposing of pristine materials inside the 
nucleus after its perihelion passage. Observations at pre- and post-perihelion 
provide us precious information on the dust evolution of the comet. The comet 
C/2012 S1 (ISON), along with two other comets, is an unparalleled target for 
this study.