(Proposal ID) S13A-062

(PI) Matsunaga, Noriyuki

(Proposal Title)
Kinematics of old bulge Miras and the early phase of the Nuclear Stellar Disk

(Abstract)
The Nuclear Stellar Disk (NSD) in our Galaxy, within ~200 parsec around Sgr 
A*, is an interesting region for studying the galaxy evolution. It is 
considered to have been produced in a secular process related to the Galactic 
disk and bar. Stars of various ages, which indicate sustained star formation, 
as well as interstellar gas and dust are found to be rotating in the NSD. So 
far, SiO maser sources, i.e.~mass-losing red giants, aged up to a few Gyr are 
the oldest tracer which has been confirmed in this system. Here we propose an 
observational test to see if low-mass stars as old as ~10 Gyr exist in the NSD.
 For this purpose, short-period Miras serve as useful tracers because they are 
significantly older than the SiO maser sources and we determined their 
distances based on their period-luminosity relation. In order to discriminate 
Miras in the NSD, if any, from those in the classical bulge dominated by old 
stars, it is critical to see their kinematics: are they rotating rapidly as 
expected for the NSD components? FMOS is an ideal tool to measure kinematics 
of our tracers, more than 200 short-period Miras distributed in a half-degree 
region. If we find a group of short-period Miras rotating around the Sgr A^*, 
this gives the first evidence for the formation of the NSD in the early phase 
of the Galaxy.