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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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 46 302 Extinction values and column densities for program stars
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
Bytes Format Units Label Explanations
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)
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); 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, their table 2, for #Field stars; Cook et al. 2011ApJ...730..124C, their table 3 for YSOs), all other values are calculated using the method described in Section 3.2.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 21-Jun-2012
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