[P-CG24] New Developments of Planetary Sciences with ALMA

[PCG24-07] A CONSTRAINT ON THE AMOUNT OF HYDROGEN FROM THE CO CHEMISTRY IN DEBRIS DISKS

*Hiroshi Kobayashi¹, Kazunari Iwasaki^2,4, Aya Higuchi³ (1.Department of Physics, Nagoya University, 2.NAOJ, 3.RIKEN, 4.Osaka University)

Keywords:Gas depletion in protoplanetar disks, Gaseous debris disks, planet formation

The faint CO gases in debris disks are easily dissolved into C by UV irradiation so that the ratio of C to CO may show the reformation rate of CO depending on the amount of underlying hydrogen molecules. We conduct radiative transfer calculations with chemical reactions for debris disks. We find the C/CO ratio is proportional to the far UV flux and the hydrogen nucleus number density. Using the deriving formula for the C/CO ratio, we give a constraint on the amount of hydrogen for debris disks around 49 Ceti with age ~ 40 Myr; the hydrogen nucleus density ~ 2x10^{-8} cm^{-3}. That implies that the debris disk contains tenuous gases caused by the depletion of a protoplanetary disk.