2010/03/30 by Th. Henning, D. Semenov, S. Guilloteau +10
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Chemistry #Emission spectrum #Excitation #Excitation temperature #Molecular Spectroscopy and Structure #Optics #Physics #Plateau de Bure Interferometer #Spectral line #Star formation #Stars #T Tauri star #Wavelength #astro-ph.GA #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/714/2/1511
23 pages, 9 figures, 3 tables, accepted for publication in ApJ
arxiv created 2010/03/30 · openalex publication_date 2010/04/20 · arxiv updated 2015/05/18 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.