(Proposal ID) S11A-124

(PI) Ishigaki, Miho

(Proposal Title)
Tracking the Orbit of a Tidally Disrupting Globular Cluster Palomar 5

(Abstract)
Palomar 5 (Pal 5) is the only known Galactic globular cluster which has a 
remarkably long tidal stream spanning > 20 deg on the sky. This narrow, 
kinematically cold stream is an excellent tracer of the Galactic gravitational 
potential at the remote halo location of ~ 18 kpc distant from the Galactic 
center. Here, we propose a FOCAS multi-object spectroscopy for > 250 candidate 
red giant/horizontal branch stars to measure radial velocities and 
metallicities covering the longest angular extent along the stream to date. 
Spectral features including two of the Calcium triplet lines in the range 
7500-8600Angstrom will be used to measure radial velocities accurate to ~ 2 km 
s^-1 and metallicity to ~ 0.3 dex from spectra obtained with VPH800 grism with 
a spectral resolution of R ~ 7000. These data will enable to identify fainter 
member stars than previous studies and thus significantly expand the sample of 
genuine member of Pal 5. Tracing the orbit using these radial velocity along 
the stream not only precisely constrain the potential but also has an 
implication on the dynamical evolution of this disrupting Pal 5.