CHEMISTRY IN DISKS. III. PHOTOCHEMISTRY AND X-RAY DRIVEN CHEMISTRY PROBED BY THE ETHYNYL RADICAL (CCH) IN DM Tau, LkCa 15, AND MWC 480

Journal Article · Mon May 10 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/714/2/1511· OSTI ID:21448822

Henning, Th; Semenov, D; Launhardt, R ^[1]; Guilloteau, St; Dutrey, A; Hersant, F; Wakelam, V ^[2]; Chapillon, E ^[3]; Pietu, V ^[4]; Schreyer, K ^[5]

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1. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany)
2. Universite de Bordeaux 1, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France)
3. Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)
4. IRAM, 300 rue de la piscine, F-38406 Saint Martin d'Heres (France)
5. Astrophysikalisches Institut und Universitaets-Sternwarte, Schillergaesschen 2-3, 07745 Jena (Germany)

We studied several representative circumstellar disks surrounding the Herbig Ae star MWC 480 and the T Tauri stars LkCa 15 and DM Tau at (sub-)millimeter wavelengths in lines of CCH. Our aim is to characterize photochemistry in the heavily UV-irradiated MWC 480 disk and compare the results to the disks around cooler T Tauri stars. We detected and mapped CCH in these disks with the IRAM Plateau de Bure Interferometer in the C and D configurations in the (1-0) and (2-1) transitions. Using an iterative minimization technique, the CCH column densities and excitation conditions are constrained. Very low excitation temperatures are derived for the T Tauri stars. These values are compared with the results of advanced chemical modeling, which is based on a steady-state flared disk structure with a vertical temperature gradient, and a gas-grain chemical network with surface reactions. Both model and observations suggest that CCH is a sensitive tracer of the X-ray and UV irradiation. The predicted radial dependency and source-to-source variations of CCH column densities qualitatively agree with the observed values, but the predicted column densities are too low by a factor of several. The chemical model fails to reproduce high concentrations of CCH in very cold disk midplane as derived from the observed low excitation condition for both the (1-0) and (2-1) transitions.

• OSTI ID: 21448822
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 714; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BINARY STARS
CALCULATION METHODS
CHEMISTRY
ERUPTIVE VARIABLE STARS
INTERFEROMETERS
ITERATIVE METHODS
MEASURING INSTRUMENTS
PHOTOCHEMISTRY
PROTOPLANETS
RADICALS
STARS
STEADY-STATE CONDITIONS
T TAURI STARS
TEMPERATURE GRADIENTS
VARIABLE STARS
WAVELENGTHS