A Constraint on the Amount of Hydrogen from the CO Chemistry in Debris Disks

Abstract The faint CO gases in debris disks are easily dissolved into C by UV irradiation, while can be reformed via reactions with hydrogen. abundance ratio of C/CO could thus a probe the amount hydrogen disks. We conduct radiative transfer calculations chemical for For typical dust-to-gas mass disks, formation proceeds without involvement H 2 because small dust grains makes inefficient. find that to number density depends on combination n Z 0.4 χ −1.1 , where is nucleus density, metallicity, and far-UV flux normalized Habing flux. Using an analytic formula we give constraints metallicity accelerated excited when either increased or energy barrier chemisorption surface decreased. This acceleration occurs only shielding effects insignificant. In shielded regions, fractions almost independent parameters grains.