Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2S032

Complex Organic Molecules in Protoplanetary Disks

Walsh, Catherine (Leiden Observatory)
Millar, Tom (Queen\'s University Belfast)
Nomura, Hideko (Kyoto University)
Herbst, Eric (University of Virginia)
Widicus Weaver, Susanna (Emory University)
Aikawa, Yuri (Kobe University)
Laas, Jake (Emory University)
Vasyunin, Anton (University of Virginia)

Protoplanetary disks are vital objects in star and planet formation, containing the material which may form a planetary system orbiting the new star. Traditionally, small, simple molecules have been detected in protoplanetary disks; however, we expect the molecular inventory of protoplanetary disks to significantly increase in the ALMA era. We investigate the synthesis of complex organic molecules (COMs) in protoplanetary disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA. We have coupled a 2D steady-state physical model of a protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs typically used for hot core/corino models. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ∼ 1.0e-6 to 1.0e-4 that of the gas number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances that their grain-surface equivalents, ∼ 1.0e-12 to 1.0e-7. Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. We get good agreement with the line transitions of H2CO observed towards TW Hya. Our synthesised line strengths for CH3OH are consistent with upper limits determined towards all sources. Our models suggest CH3OH should be readily observable in nearby protoplanetary disks with ALMA; however, more complex species may prove challenging, even with ALMA ‘Full Science’ capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets formed via the coagulation of icy grains in the Sun’s natal protoplanetary disk.

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