Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812104q&link_type=abstract
American Astronomical Society, AAS Meeting #218, #121.04; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We report Submillimeter Array (SMA) observations of multiple lines of CO (J=2-1, 3-2 and 6-5) and CO isotopologues (13CO J=2-1, C18O J=2-1 and C17O J=3-2) in the disk around the Herbig Ae star HD 163296 at 2 arcsec (250 AU) resolution, and we interpret these data in the framework of a model that constrains the radial and vertical location of the line emission regions. We first develop a set of physically self-consistent accretion disk models with exponentially tapered edges that reproduces the observed spectral energy distribution and spatially resolved millimeter dust continuum emission. We further constrain the vertical structure of the model, taking advantage of the wide range of excitation sampled by the multiple optically thick CO lines, in particular the rarely observed J=6-5 line. The resulting model has a cold midplane populated by large grains with a large scale height. Using this model, we fit for the location of the optically thinner CO isotopologue line emissions and find they are confined between two vertical boundaries: a lower boundary around 19 K (due to CO freeze-out) and an upper boundary where the surface density is around 1021 cm-2 (due to photodissociation). If all CO isotopologues freeze out at 19 K, then we find isotopic ratios of 12C/13C, 16O/18O and 18O/17O consistent with the quiescent interstellar gas-phase values. We discuss the relevance of the CO freeze-out on the determination of the fractional abundances of CO and its isotopologues.
Andrews S. A.
Ayala Sandra
D'Alessio Paola
Hughes Meredith A.
Oberg Karin I.
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