(Proposal ID) S13A-093

(PI) Oka Takeshi

(Proposal Title)
Expanding Molecular Ring in the Galactic center studied by H_3^+

(Abstract)
We propose to observe infrared spectra of the L band H_3^+ and the K band CO 
toward newly found dust embedded stars from 140 pc West of SgrA* to 120 pc 
East covering wide regions of the Central Molecular Zone (CMZ), the center of 
activities in the Galactic center. The goal of this project is two fold. 
(1) We will determine ionization rate, temperature, and density of diffuse 
clouds over wide ranges of the CMZ. Our previous observations have shown high 
ionization rate zeta > 2 x 10^-15 s^-1 of the environment and a vast amount of 
warm (T ~250 K), and diffuse (n < 100 cm^-3) gas. The proposed observations 
will greatly extend the range of study and give estimate of the volume filling 
factor. (2) We launch a new project of studying the Expanding Molecular Ring 
previously revealed from observations of dense clouds by radio lines.  Our use 
of large scale diffuse clouds and ubiquitous H_3^+ will provide more definitive
 characteristics of the EMR.  The IRCS with wide wavelength coverage is ideal 
for this study in which we need to observe three H_3^+ lines.