(Proposal ID) S16A-129

(PI) Matsunaga, Noriyuki

(Proposal Title)
Kinematics and metallicities of Cepheids hidden in the Milky Way disk

(Abstract)
The severe interstellar extinction in the Galactic disk and the consequent 
scarcity of the observed samples have postponed our understanding of the 
structure and evolution of the inner parts of the Milky Way. Cepheids are a 
good tracer of the Milky Way thanks to their brightness and the availbility of 
their accurate distances and ages, 10-300Myr, from the period--luminosity and 
period-age relations. For example, they show a clearer and tighter metallicity 
gradient (averageous metallicity as a function of the Galactocentric distance) 
of the disk than any other tracers. While survey of the Cepheids in the hidden 
parts of the disk is still incomplete, our recent surveys in the infrared have 
brought us new samples located in the obscured regions. We here propose to 
measure radial velocities and metallicities of the newly discovered Cepheids 
behind the bulge and those at 60-80 deg in Galactic longitude but further than 
5 kpc. Their radial velocities will be useful to identify spiral arms to which 
the Cepheids belong, and these Cepheids would be the first stars, at their 
locations, with the kinematic components identified. Furthermore, our targets 
occupy uncultivated regions in terms of Galactocentric distance and Galactic 
Azimuth, thus give a new insight into metallicity distribution of relatively 
young stars.