J/ApJ/720/259    CO column densities in dark clouds             (Whittet+, 2010)
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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
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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 CO_2_ (which
    forms by oxidation of CO on the dust), we find that the total column
    density (gas+solid) correlates tightly with visual extinction (A_V_)
    over the range 5mag<A_V_<30mag, i.e., up to the highest extinctions
    covered by our sample. The mean depletion of gas-phase CO, expressed
    as {delta}(CO)=N(CO)_ice_/N(CO)_total_, increases monotonically from
    negligible levels for A_V_<~5 to ~0.3 at A_V_=10 and ~0.6 at A_V_=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); 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.
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History:
    From electronic version of the journal

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(End)                 Greg Schwarz [AAS], Emmanuelle Perret [CDS]    21-Jun-2012