ALMA Science Verification data for the circumstellar disk around HD 163296

Vol. 557
In section 6. Interstellar and circumstellar matter

Unveiling the gas-and-dust disk structure in HD 163296 using ALMA observations

ALMA imaging of the CO snowline of the HD 163296 disk with DCO+

The understanding of circumstellar disks and planet formation is one of the many research areas posed to gain immense growth with the advent of the Atacama Large Millimeter Array (ALMA). Two papers published this week, de Gregorio-Monsalvo et al. (2013) and Mathews et al. (2013), present ALMA Science Verification data for the circumstellar disk around HD 163296, a 5 Myr Herbig Ae star at a distance of 122 pc, to address questions on the physical and chemical structure of this disk. Gregorio-Monsalvo et al. study the structure of the protoplanetary disk surrounding the Herbig Ae star CO(3­2) emission and unveil for the first time at submillimeter frequencies the vertical structure of the disk in Keplerian rotation, revealing the back and the front of a flared disk. They also find that the gaseous disk is more than two times larger than the dust disk, with a similar critical radius but with a shallower radial profile. Mathews et al. use emission from the DCO+ line to directly resolve the CO "snowline", the region at which the gas-phase CO abundance drops as a result of freeze out. These authors infer local enhancements of the abundance of DCO+ on the order of 10⁴ suggesting that the ionization fraction must be three orders of magnitude higher than necessary to maintain the MHD turbulence that powers viscous accretion.