(Proposal ID) S12A-031

(PI) Iye, Masanori

(Proposal Title)
The first AO188 astrometry: Propoer motion of stars in M13

(Abstract)
Stars in a globular cluster M13 located at 7.7kpc are clearly resolved by 
Subaru AO188/IRCS imaging. We study the proper motion of stars in M13, by 
making astrometric comparison of stellar positions on AO188/IRCS images and 
on existing HST/ACS images (1999) as well as on Subaru AO36/IRCS images 
(2001-2002). The mean proper motion of stars in M13 is estimated to be about 
4 mas over 10 years span, according to the classic studies of photographic 
plates and also from the virial estimates using radial velocity measurements. 
As the PSF of AO188 can be as sharp as 60mas, careful analysis taking the 
field distorsions and the PSF variation across the field into account will 
provide astrometric error as small as 1 mas. The proposed study will provide 
clear membership identification to study its CMD clean from contaminants. By 
combining the data with radial velocity measurements, one can re-construct 
orbital motion of stars in 3D to constrain the gravitational potential and 
hence the distribution of dark matter.