1:45 PM - 2:00 PM
[PCG19-07] Measurability of CO isotopologue ratio in PPDs with ALMA
Keywords:protoplanetary disk, astrochemistry, oxygen isotope anomaly
Detailed measurement of materials such as meteorites, solar wind, and water on the Earth reveals oxygen isotope anomaly in the solar system. Since the three-oxygen isotope diagram of the materials in the solar system falls along the one-slope line, it is presumed that mass-independent isotope fractionation played a key role. As the fractionation mechanism, isotope selective photodissociation of carbon monoxide (CO) in the presolar cloud and/or presolar nebula has been theoretically suggested. However, observational evidence remains insufficient.
In recent years, thanks to the progress in the astronomical instrument such as Atacama Large Millimeter/Sub-millimeter Array (ALMA), detailed observations of nearby protoplanetary disks have become possible. If the oxygen isotope anomaly observed in the present solar system was established in the presolar cloud or presolar nebula, the similar mechanism would be at work in protoplanetary disks, which we can observe with ALMA.
We discuss a method for directly measuring the CO isotopologue ratio in protoplanetary disks. CO gas in protoplanetary disks is generally observed as emission lines in radio. It is difficult to estimate the total amount of the CO gas because the line centers are optically thick for 12C16O and 13C16O. Even so, the line wings can be optically thin, and it is possible to estimate the isotopologue column density ratio in principle.
First, we calculated the physical and chemical structure of a typical protoplanetary disk with chemical reaction networks. Second, we executed the one-dimensional radiative transfer simulation. Then, we simulate the ALMA observations of the protoplanetary disk. As a result, the CO isotopologue ratio can be constrained using the line wings with the observations in high spatial (~15 au) and velocity (~0.1 km/s) resolution if the disk is edge-on.
In recent years, thanks to the progress in the astronomical instrument such as Atacama Large Millimeter/Sub-millimeter Array (ALMA), detailed observations of nearby protoplanetary disks have become possible. If the oxygen isotope anomaly observed in the present solar system was established in the presolar cloud or presolar nebula, the similar mechanism would be at work in protoplanetary disks, which we can observe with ALMA.
We discuss a method for directly measuring the CO isotopologue ratio in protoplanetary disks. CO gas in protoplanetary disks is generally observed as emission lines in radio. It is difficult to estimate the total amount of the CO gas because the line centers are optically thick for 12C16O and 13C16O. Even so, the line wings can be optically thin, and it is possible to estimate the isotopologue column density ratio in principle.
First, we calculated the physical and chemical structure of a typical protoplanetary disk with chemical reaction networks. Second, we executed the one-dimensional radiative transfer simulation. Then, we simulate the ALMA observations of the protoplanetary disk. As a result, the CO isotopologue ratio can be constrained using the line wings with the observations in high spatial (~15 au) and velocity (~0.1 km/s) resolution if the disk is edge-on.