S22B0104
S22B0104
The abundance gradient refers to the radial profile of chemical abundances of gas and stars as a function of galactocentric distance. Many disk galaxies show the negative gradient (the abundance of the outer disk being lower), but the slope often (not always) gets shallower in the outer disk. This flattening feature is expected to be caused by (re-)accretion of gas and radial migration of gas and stars, although the detailed theory is not yet established for explaining the frequency and the time evolution of this feature. Recent results support that the outer-disk flattening also occurs in the Milky Way disk when it is traced with old stars (> a few Gyr), but we still lack the observational data for young stars (<200 Myr) and gas in the same regions. In our survey of variable stars in the northern Galactic plane, we found over 30 Cepheids at 14 kpc or further away from the Galactic center. They are faint in the optical because of the interstellar extinction, but near-infrared spectroscopy would provide precise abundances (iron and several other elements). This sample would be the first to give a solid conclusion on the flattening traced with young stars which are not yet affected by radial migration, thereby giving essential information on the gas used for the current star formation in the outer disk.
This document was translated from LATEX by HEVEA.