Hydrostatic Equilibrium Does Not Solve the C18O Flux Problem in Protoplanetary Disks

Abstract

ALMA observations have shown that there is discrepancy between the disk mass estimate from CO emission and disk masses estimated from other tracers. This discrepancy has been interpreted as lower than expected CO abundance in the warm, surface layers of the disk. Recent work by Ruaud et al. claims that the low observed C18O fluxes can be explained with a ISM abundance of CO, that is 10−4 w.r.t. H2 by including hydrostatic equilbrium in the model density setup. We show that the Ruaud et al. low CO fluxes are due to an unrealistic temperature structure in the outer disk, due to an interaction of their dust model and hydrostatic equilibrium at their inner model edge. Furthermore, we show with our own modeling that a parametric model does a better job at matching the measured outer disk temperature structure.