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J.E. Enriquez (UTEP), I. Kamp (ESA/STScI)
CO emission lines have been used to observe Circumstellar Disks around A-type stars. Combined CO gas and IR dust observations have detected a gas-to-dust ratio much lower than the interstellar gas-to-dust ratio. The reason is that CO is a poor tracer of gas; most of the gas is in the form of H2. The main motivation of the project was twofold: (1) to show at which disk masses CO ceases to be a good tracer of the disk mass and (2) how reliable and sensitive other tracers such as C, C+ and O will be using future instruments such as SOFIA, Herschel, APEX and ALMA. Emission line calculations are based on the disk models of Kamp & Bertoldi (2000) and Kamp & van Zadelhoff (2001). The 2D Monte Carlo radiative transfer code from Hogerheijde & van der Tak (2000) was used to calculate the line emission from the optically thin disk models. Four different disk masses were used - spanning four orders of magnitude - to create the line profiles for CO and O. The integrated line fluxes for typical distance and inclination are presented here to enable an approximation of the disk mass from the observations. Contrary to previous studies - that assume constant conversion factors - these new results take into account the varying tracer abundance and excitation temperature within the disk. We acknowledge the Summer Student Program at STScI for the support of this project.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.