(Proposal ID) S12A-053

(PI) Matsunaga, Noriyuki

(Proposal Title)
Evolution of the Galactic Nuclear Bulge traced with Cepheid variable stars

(Abstract)
The Nuclear Bulge is the stellar population of ~200 parsecs in radius found in 
the center of the Milky Way. Containing young stars, a few Myr old, it is 
considered that the Nuclear Bulge experienced sustained star formation over 
the lifetime of the Milky Way. Such star formation is important in considering 
gas circulation and consumption within the Milky Way and evolution of the 
Bulge. However, its star formation history and the characteristics of the 
stars formed there remain to be investigated. Our recent discovery of 
classical Cepheid variable stars (~25 Myr old) has revealed stars of a few 
tens of Myr for the first time. In addition, we have discovered a few Cepheids 
in the inner disk (at the distances of 4--5 kpc from the Galactic Centre). We 
propose spectroscopic (and imaging) observations of the Cepheids to study 
chemical evolution of the Nuclear Bulge. The measurements of the chemical 
abundances like [Fe/H] and [alpha/Fe] of the Cepheids would give the first 
measurement of the interstellar matter chemistry in the Nuclear Bulge a few 
tens of Myr ago. Comparing their abundances with those of the inner-disk 
Cepheids and young stars (a few Myr old) in the Nuclear Bulge, it becomes 
possible to trace temporal evolution in and around the Nuclear Bulge.