AAS 207th Meeting, 8-12 January 2006
Session 9 Circumstellar Disks I
Poster, Monday, 9:20am-7:00pm, January 9, 2006, Exhibit Hall

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[9.11] Stratification of Gas and Dust around Young Stellar Disks

T. Rettig (University of Notre Dame), S. Brittain (NOAO), E. Gibb (Univ. St. Louis, Missouri), D. Balsara (University of Notre Dame), T. Simon (University of Hawaii)

We present the first direct observational verification and theoretical modeling of the stratification of gas and dust in disks around young stellar objects (YSOs). The physical structure of extended flared disks around YSOs depends on a variety of parameters including the extent of gas and dust mixing (i.e. turbulence), the rate of dust settling and the process of grain coagulation. In this work, we present line of sight measurements of the column density of gas and dust for four YSOs having different inclinations and extinctions but similar ages. Because dust particles are expected to settle to the midplane around YSOs, The line of sight gas/dust ratios for each inclination provides a direct measure of the dust settling and indirectly provides a constraint on the midplane turbulence. The measurements provide the first observational evidence and initial quantification of the stratification of gas and dust in the extended disks around very young stellar objects that are probably in the early stages of planet formation. The implications of this analysis are that 1) gas and dust do indeed settle at different rates, 2) the role of settling in the extended disks can be constrained by the observations and 3) the inclusion of turbulent velocities not only provide a mechanism to support smaller grains at large scale heights but also also provide a mechanism to constrain turbulence in the midplane. This interpretation of turbulence will not impede the sedimentation of larger dust particles to the midplane and the subsequent formation of planetesimals.

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