Oberg, KarinFuruya, KenjiLoomis, RyanAikawa, YuriAndrews, SeanQi, ChunhuaDishoeck, Ewine F. vanWilner, David2016-01-212015Öberg, Karin I., Kenji Furuya, Ryan Loomis, Yuri Aikawa, Sean M. Andrews, Chunhua Qi, Ewine F. van Dishoeck, and David J. Wilner. 2015. “Double DCO+ rings reveal CO ice desorption in the outer disk around IM Lup” The Astrophysical Journal 810 (2) (September 4): 112. doi:10.1088/0004-637x/810/2/112.1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:24820075In 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, C18O 2–1, H13CO+ 3–2 and DCO+ 3–2 emission at ~0farcs5 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 ~0farcs6 and 2'' (~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.en-USJournal Article2016-01-09Oberg, K.I., Furuya, K., Loomis, R., Aikawa, Y., Andrews, S.M., Qi, C., van Dishoeck, E.F., Wilner, D.J.2016-01-2110.1088/0004-637X/810/2/112