(Proposal ID) S17B-105

(PI) Chiba, Masashi

(Proposal Title)
Spectroscopy of a new Milky Way satellite discovered in the HSC survey I.

(Abstract)
We launch a spectroscopic follow-up campaign for new ultra-faint dwarf galaxies
in the Milky Way discovered by our group from the Hyper Suprime-Cam (HSC) 
survey data. This proposal intends to target one of these new ultra-faint 
dwarf galaxies being observable in S17B, named Cetus III (Homma et al. 2017). 
This galaxy is located at a heliocentric distance of 251^{+24}_{-11}kpc with a 
most likely absolute magnitude of M_V = -2.4+-0.6 mag, namely beyond the reach 
of SDSS but within the delection limit of Subaru/HSC. Medium resolution 
spectroscopy of candidate bright member stars in Cetus@III, including red 
giant branch and asymptotic giant branch stars, as well as candidate field 
halo stars in the same direction, will allow us to assess the membership in 
Cetus@III through the analysis of their radial velocities. These kinematical 
data also provide basic information for dynamical mass associated with a 
surrounding dark halo of Cetus III. Combined with metallicity measurements for 
candidate member stars, we will constrain the basic chemo-dynamical properties 
of this newly discovered ultra-faint dwarf galaxy.