652 research outputs found
Chemistry in Protoplanetary Disks
This comprehensive review summarizes our current understanding of the
evolution of gas, solids and molecular ices in protoplanetary disks. Key
findings related to disk physics and chemistry, both observationally and
theoretically, are highlighted. We discuss which molecular probes are used to
derive gas temperature, density, ionization state, kinematics, deuterium
fractionation, and study organic matter in protoplanetary disks.Comment: 83 pages, 8 figures, 5 tables, to be published in a Thematic Issue
"Astrochemistry" in Chem. Reviews (December 2013). This document is the
unedited Author's version of a Submitted Work that was subsequently accepted
for publication in Chemical Reviews, copyright (c) American Chemical Society
after peer revie
Gas mass tracers in protoplanetary disks: CO is still the best
Protoplanetary disk mass is a key parameter controlling the process of
planetary system formation. CO molecular emission is often used as a tracer of
gas mass in the disk. In this study we consider the ability of CO to trace the
gas mass over a wide range of disk structural parameters and search for
chemical species that could possibly be used as alternative mass tracers to CO.
Specifically, we apply detailed astrochemical modeling to a large set of models
of protoplanetary disks around low-mass stars, to select molecules with
abundances correlated with the disk mass and being relatively insensitive to
other disk properties. We do not consider sophisticated dust evolution models,
restricting ourselves with the standard astrochemical assumption of m
dust. We find that CO is indeed the best molecular tracer for total gas mass,
despite the fact that it is not the main carbon carrier, provided reasonable
assumptions about CO abundance in the disk are used. Typically, chemical
reprocessing lowers the abundance of CO by a factor of 3, compared to the case
of photo-dissociation and freeze-out as the only ways of CO depletion. On
average only 13% C-atoms reside in gas-phase CO, albeit with variations from 2
to 30%. CO, HO and HCO can potentially serve as alternative mass
tracers, the latter two being only applicable if disk structural parameters are
known.Comment: Accepted for publication in Ap
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