A new measurement method of isotopologue ratios in protoplanetary disks: a case study of the 12CO/13CO ratio in the TW Hya disk
speaker: Tomohiro Yoshida
Abstract:
Planetary systems are thought to be born in protoplanetary disks. Isotope ratios are a powerful tool for investigating the material origin and evolution from molecular clouds to planetary systems via protoplanetary disks. However, it is challenging to measure the isotope (isotopologue) ratios, especially in protoplanetary disks, because the emission lines of major species are saturated. We developed a new method to overcome these challenges by using optically thin line wings induced by thermal broadening. As a first application of the method, we measured the 12CO/13CO ratio in the TW Hya protoplanetary disk. 12CO/13CO was estimated to be ~23, which is significantly smaller than the typical ISM value (~69) in the inner disk. In contrast, it is suggested that 12CO/13CO is higher than >100 in the outer disk. Our results imply that the gas-phase 12CO/13CO can vary by a factor of >5 even inside a protoplanetary disk, and therefore, can be used to trace material evolution in disks.