DOUBLE DCO+ RINGS REVEAL CO ICE DESORPTION IN THE OUTER DISK AROUND IM LUP

作者：Oeberg Karin I; Furuya Kenji; Loomis Ryan; Aikawa Yuri; Andrews Sean M; Qi Chunhua; van Dishoeck Ewine F; Wilner David J

来源：Astrophysical Journal, 2015, 810(2): 112.

DOI：10.1088/0004-637X/810/2/112

• astrochemistry
• circumstellar matter
• molecular processes
• protoplanetary disks
• radio lines: ISM
• techniques: imaging spectroscopy

In a protoplanetary disk, a combination of thermal and non-thermal desorption processes regulate where volatiles are liberated from icy grain mantles into the gas phase. Non-thermal desorption should result in volatile-enriched gas in disk-regions where complete freeze-out is otherwise expected. We present Atacama Large Millimeter/Submillimeter Array observations of the disk around the young star IM Lup in 1.4 mm continuum, (CO)-O-18 2-1, (HCO+)-C-13 3-2 and DCO+ 3-2 emission at approximate to 0 ''.5 resolution. The images of these dust and gas tracers are clearly resolved. The DCO+ line exhibits a striking pair of concentric rings of emission that peak at radii of similar to 0 ''.6 and 2 '' (similar to 90 and 300 AU, respectively). Based on disk chemistry model comparison, the inner DCO+ ring is associated with the balance of CO freeze-out and thermal desorption due to a radial decrease in disk temperature. The outer DCO+ ring is explained by non-thermal desorption of CO ice in the low-column-density outer disk, repopulating the disk midplane with cold CO gas. The CO gas then reacts with abundant H2D+ to form the observed DCO+ outer ring. These observations demonstrate that spatially resolved DCO+ emission can be used to trace otherwise hidden cold gas reservoirs in the outmost disk regions, opening a new window onto their chemistry and kinematics.

• 出版日期2015-9-10