Systematic observations on Galactic Interstellar isotope ratios

摘要

We are performing systematic observation studies on the Galactic interstellar isotopic ratios, including ~(18)O/~(17)O, ~(12)C/~(13)C, ~(14)N/~(15)N and ~(32)S/~(34)S. Our strategy focuses on combination of multi-transition observation data toward large samples with different Galactocentric distances. Our preliminary results show positive Galactic radial gradients of ~(18)O/~(17)O and ~(12)C/~(13)C. In both cases, the ratio increases with the Galactocentric distance, which agrees with the inside-out scenario of our Galaxy. Observations of other isotopes such as ~(14)N/~(15)N and ~(32)S/~(34)S are on-going.