J/ApJ/720/259 CO column densities in dark clouds (Whittet+, 2010)
The uptake of interstellar gaseous CO into icy grain mantles in a quiescent
dark cloud.
Whittet D.C.B., Goldsmith P.F., Pineda J.L.
<Astrophys. J., 720, 259-265 (2010)>
=2010ApJ...720..259W 2010ApJ...720..259W
ADC_Keywords: Molecular clouds ; Extinction ; Abundances ; Interstellar medium ;
Radio lines
Keywords: dust, extinction - ISM: abundances -
ISM: individual objects (Taurus Dark Cloud) - ISM: molecules
Abstract:
Data from the Five College Radio Astronomy Observatory CO Mapping
Survey of the Taurus molecular cloud are combined with extinction data
for a sample of 292 background field stars to investigate the uptake
of CO from the gas to icy grain mantles on dust within the cloud. On
the assumption that the reservoir of CO in the ices is represented
well by the combined abundances of solid CO and solid CO2 (which
forms by oxidation of CO on the dust), we find that the total column
density (gas+solid) correlates tightly with visual extinction (AV)
over the range 5mag<AV<30mag, i.e., up to the highest extinctions
covered by our sample. The mean depletion of gas-phase CO, expressed
as δ(CO)=N(CO)ice/N(CO)total, increases monotonically from
negligible levels for AV≲5 to ∼0.3 at AV=10 and ∼0.6 at AV=30.
As these results refer to line-of-sight averages, they must be
considered lower limits to the actual depletion at loci deep within
the cloud, which may approach unity. We show that it is plausible for
such high levels of depletion to be reached in dense cores on
timescales ∼0.6Myr, comparable with their expected lifetimes.
Dispersal of cores during star formation may be effective in
maintaining observable levels of gaseous CO on the longer timescales
estimated for the age of the cloud.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 46 302 Extinction values and column densities for program
stars
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJS/176/457 : Taurus dark cloud background star catalog (Shenoy+, 2008)
J/ApJ/678/985 : c2d Spitzer survey of interstellar ices. I. (Boogert+, 2008)
J/A+A/421/1087 : CO abundance of 3 globules (Harjunpaa+, 2004)
J/ApJ/517/264 : Extinction in the Taurus dark cloud complex (Arce+, 1999)
J/ApJS/101/117 : UBVRIJHKLMNQ photometry in Taurus-Auriga (Kenyon+ 1995)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/302] Running number
5- 21 A17 --- ID Source identification (1)
23- 26 F4.1 mag A(V) Visual extinction
28- 32 F5.2 10+17cm-2 N(CO)gas Gas phase CO column density (2)
34- 39 F6.2 10+17cm-2 N(CO)ice ? Solid phase CO column density (3)
41- 46 F6.2 10+17cm-2 N(CO2)ice ? Solid phase CO2 column density (3)
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Note (1): Field stars from Shenoy et al. 2008, Cat. J/ApJS/176/457 (n=1-247)
designated by 2MASS catalog number; additional field stars (n=248-292)
mostly designated by Henry Draper (HD) catalog number (Whittet et al.
2001ApJ...547..872W 2001ApJ...547..872W); YSOs (n=293-302) designated by 2MASS catalog number.
Note (2): From present work.
Note (3): Direct measurements are included where available (Whittet et al.
2007ApJ...655..332W 2007ApJ...655..332W, their table 2, for #Field stars; Cook et al.
2011ApJ...730..124C 2011ApJ...730..124C, their table 3 for YSOs), all other values are
calculated using the method described in Section 3.2.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 21-Jun-2012