The effect of carbon grain destruction on the chemical structure of protoplanetary disks. (arXiv:1811.10194v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wei_C/0/1/0/all/0/1">Chen-En Wei</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nomura_H/0/1/0/all/0/1">Hideko Nomura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_J/0/1/0/all/0/1">Jeong-Eun Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ip_W/0/1/0/all/0/1">Wing-Huen Ip</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Walsh_C/0/1/0/all/0/1">Catherine Walsh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Millar_T/0/1/0/all/0/1">T. J. Millar</a>
The bulk composition of the Earth is dramatically carbon poor compared to
that of the interstellar medium, and this phenomenon extends to the asteroid
belt. To interpret this carbon deficit problem, the carbonaceous component in
grains must have been converted into the gas-phase in the inner regions of
protoplanetary disks prior to planetary formation. We examine the effect of
carbon grain destruction on the chemical structure of disks by calculating the
molecular abundances and distributions using a comprehensive chemical reaction
network. When carbon grains are destroyed and the elemental abundance of the
gas becomes carbon-rich, the abundances of carbon-bearing molecules, such as
HCN and carbon-chain molecules, increase dramatically near the midplane, while
oxygen-bearing molecules, such as H$_2$O and CO$_2$, are depleted. We compare
the results of these model calculations with the solid carbon fraction in the
solar system. Although we find a carbon depletion gradient, there are some
quantitative discrepancies: the model shows a higher value at the position of
asteroid belt and a lower value at the location of the Earth. In addition,
using the obtained molecular abundances distributions, coupled with line
radiative transfer calculations, we make predictions for ALMA to potentially
observe the effect of carbon grain destruction in nearby protoplanetary disks.
The results indicate that HCN, H$^{13}$CN and c-C$_3$H$_2$ may be good tracers.
The bulk composition of the Earth is dramatically carbon poor compared to
that of the interstellar medium, and this phenomenon extends to the asteroid
belt. To interpret this carbon deficit problem, the carbonaceous component in
grains must have been converted into the gas-phase in the inner regions of
protoplanetary disks prior to planetary formation. We examine the effect of
carbon grain destruction on the chemical structure of disks by calculating the
molecular abundances and distributions using a comprehensive chemical reaction
network. When carbon grains are destroyed and the elemental abundance of the
gas becomes carbon-rich, the abundances of carbon-bearing molecules, such as
HCN and carbon-chain molecules, increase dramatically near the midplane, while
oxygen-bearing molecules, such as H$_2$O and CO$_2$, are depleted. We compare
the results of these model calculations with the solid carbon fraction in the
solar system. Although we find a carbon depletion gradient, there are some
quantitative discrepancies: the model shows a higher value at the position of
asteroid belt and a lower value at the location of the Earth. In addition,
using the obtained molecular abundances distributions, coupled with line
radiative transfer calculations, we make predictions for ALMA to potentially
observe the effect of carbon grain destruction in nearby protoplanetary disks.
The results indicate that HCN, H$^{13}$CN and c-C$_3$H$_2$ may be good tracers.
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