CHEMICAL PROCESSES IN PROTOPLANETARY DISKS

Journal Article · Wed Oct 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/2/1607· OSTI ID:21464606

Walsh, Catherine; Millar, T J ^[1]; Nomura, Hideko ^[2]

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1. Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, BT7 1NN (United Kingdom)
2. Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)

We have developed a high-resolution combined physical and chemical model of a protoplanetary disk surrounding a typical T Tauri star. Our aims were to use our model to calculate the chemical structure of disks on small scales (submilliarcsecond in the inner disk for objects at the distance of Taurus, {approx}140 pc) to investigate the various chemical processes thought to be important in disks and to determine potential molecular tracers of each process. Our gas-phase network was extracted from the UMIST Database for Astrochemistry to which we added gas-grain interactions including freezeout and thermal and non-thermal desorption (cosmic-ray-induced desorption, photodesorption, and X-ray desorption), and a grain-surface network. We find that cosmic-ray-induced desorption has the least effect on our disk chemical structure while photodesorption has a significant effect, enhancing the abundances of most gas-phase molecules throughout the disk and affecting the abundances and distribution of HCN, CN, and CS, in particular. In the outer disk, we also see enhancements in the abundances of H{sub 2}O and CO{sub 2}. X-ray desorption is a potentially powerful mechanism in disks, acting to homogenize the fractional abundances of gas-phase species across the depth and increasing the column densities of most molecules, although there remain significant uncertainties in the rates adopted for this process. The addition of grain-surface chemistry enhances the fractional abundances of several small complex organic molecules including CH{sub 3}OH, HCOOCH{sub 3}, and CH{sub 3}OCH{sub 3} to potentially observable values (i.e., a fractional abundance of {approx}>10{sup -11}).

• OSTI ID: 21464606
• Journal Information: Astrophysical Journal, Vol. 722, Issue 2; Other Information: DOI: 10.1088/0004-637X/722/2/1607; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
ASTROPHYSICS
CARBON DIOXIDE
CARBON NITRIDES
COSMIC RADIATION
DESORPTION
HYDROCYANIC ACID
METHANOL
PROTOPLANETS
T TAURI STARS
WATER
X RADIATION
ALCOHOLS
BINARY STARS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
ELECTROMAGNETIC RADIATION
ERUPTIVE VARIABLE STARS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
IONIZING RADIATIONS
NITRIDES
NITROGEN COMPOUNDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICS
PNICTIDES
RADIATIONS
SORPTION
STARS
VARIABLE STARS