J/ApJ/856/85 Unlocking CO depletion in protoplanetary disks. I. (Schwarz+, 2018)
Unlocking CO depletion in protoplanetary disks.
I. The warm molecular layer.
Schwarz K.R., Bergin E.A., Cleeves L.I., Zhang Ke, Oberg K.I., Blake G.A.,
Anderson D.
<Astrophys. J., 856, 85 (2018)>
=2018ApJ...856...85S 2018ApJ...856...85S
ADC_Keywords: Models; Carbon monoxide; Abundances; Interstellar medium;
Molecular data
Keywords: astrochemistry; circumstellar matter; ISM: abundances; molecular data;
protoplanetary disks
Abstract:
CO is commonly used as a tracer of the total gas mass in both the
interstellar medium and in protoplanetary disks. Recently, there has
been much debate about the utility of CO as a mass tracer in disks.
Observations of CO in protoplanetary disks reveal a range of CO
abundances, with measurements of low CO to dust mass ratios in
numerous systems. One possibility is that carbon is removed from CO
via chemistry. However, the full range of physical conditions
conducive to this chemical reprocessing is not well understood. We
perform a systematic survey of the time dependent chemistry in
protoplanetary disks for 198 models with a range of physical
conditions. We vary dust grain size distribution, temperature,
comic-ray and X-ray ionization rates, disk mass, and initial water
abundance, detailing what physical conditions are necessary to
activate the various CO depletion mechanisms in the warm molecular
layer. We focus our analysis on the warm molecular layer in two
regions: the outer disk (100au) well outside the CO snowline and the
inner disk (19au) just inside the midplane CO snowline. After 1Myr, we
find that the majority of models have a CO abundance relative to H2
less than 10-4 in the outer disk, while an abundance less than
10-5 requires the presence of cosmic-rays. Inside the CO snowline,
significant depletion of CO only occurs in models with a high
cosmic-ray rate. If cosmic-rays are not present in young disks, it is
difficult to chemically remove carbon from CO. Additionally, removing
water prior to CO depletion impedes the chemical processing of CO.
Chemical processing alone cannot explain current observations of low
CO abundances. Other mechanisms must also be involved.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 122 198 Top five most abundant carbon bearing species in
the warm molecular layer at 100au for each model
after 1Myr
table5.dat 122 198 Top five most abundant carbon bearing species in
the warm molecular layer at 19au for each model
after 1Myr
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See also:
J/ApJ/788/59 : Parametric model for circumstellar disks gas mass
(Williams+, 2014)
J/ApJ/828/46 : ALMA survey of Lupus protoplanetary disks. I. (Ansdell+, 2016)
J/A+A/588/A108 : Spectra of CO and [CI] in protoplanetary disks (Kama+, 2016)
Byte-by-byte Description of file: table[45].dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Model Model label (1)
18- 22 F5.3 Msun Mdisk [0.003/0.1] Disk mass
24- 27 F4.2 --- fl [0/1] Fraction of large grains by mass
29- 37 A9 --- Spec1 Most abundant carbon bearing species
39- 46 E8.2 --- Abun1 [5.7e-05/0.00021] Abundance of Spec1 (2)
48- 56 A9 --- Spec2 Second most abundant carbon bearing species
58- 65 E8.2 --- Abun2 [1e-08/9.7e-05] Abundance of Spec2 (2)
67- 75 A9 --- Spec3 Third most abundant carbon bearing species
77- 84 E8.2 --- Abun3 [1.6e-09/4.4e-05] Abundance of Spec3 (2)
86- 94 A9 --- Spec4 Fourth most abundant carbon bearing species
96-103 E8.2 --- Abun4 [6.8e-10/4.1e-05] Abundance of Spec4 (2)
105-113 A9 --- Spec5 Fifth most abundant carbon bearing species
115-122 E8.2 --- Abun5 [8.6e-11/1.6e-05] Abundance of Spec5 (2)
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Note (1): Table 1 lists the set of physical conditions covered by our models.
For each disk mass, we generate a model for a range of large grain
fractions, f, from 0 to 0.99. Our fiducial model uses an X-ray
luminosity of 1030erg/s and a cosmic-ray ionization rate of
1.6x10-19s-1. The high X-ray luminosity models use an X-ray
luminosity of 1031erg/s with all other parameters the same as for
the fiducial models, while the high cosmic-ray rate models assume
ζCR=2x10-17s-1. Additionally, we consider warm disk models,
in which the gas and dust temperatures have been increased by 20K
everywhere in the disk, for the fiducial and high cosmic-ray models.
Table 1: Physical model properties:
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Parameter Values
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Mdisk (M☉) 0.1, 0.03, 0.003
LXR (erg/s) 1E30, 1E31
zetaCR (s-1) 1.6E-19, 2E-17
fl 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.99
Rin (au) 0.1
Rout (au) 200
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See section 2 for further explanations.
Note (2): Abundance relative to H2.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Feb-2019